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Science Library
364,
, W 33
V 2.
RUDIMENTARY
M I N E R A L O G Y,
FOR
THE USE OF BEGINNERS;
OR
GUIDE TO THOSE WHO ARE IN SEARCH
OF THE WALUABLE METALS
EssBNTIAL IN PRACTICAL SCIENCE. .
*.
Jºe”/3 & bºrº ,
BY Mrs. VARLEY,
AUTHOR OF ‘convertsATIONs on MINERALOGY,' AND OTHER
ESSAYS ON THE SAME SUBJECT. ' -
P A R T II.
# until un: -
JOHN WEALE,
ARCHITECTURAL LIBRARY, 59, HIGH HOLBORN.
M. D C C C, XLV l l I.
() F. MINERATLOGY. 8]
I R O N,
IRON has been found in several places as a native
metal; but beneath the surface of the earth, its
existence in this state is rare; it is disseminated
only in small particles or thin veins among iron
pyrites and hydrate of iron ; or contained in some of
the lavas both of recent and extinct volcanoes.
The large masses of native iron with which we are
acquainted, are so singular both in their situation and
external appearance, that they are now considered to
be incontestably of meteoric origin. Whatever may
have been the mode of their formation, or their
former position, there can be little doubt that they
have fallen from the atmosphere to our earth. The
times at which some of them have fallen, have been
accurately recorded”; but of others, such as the
immense mass near Jemissek in Siberia, that at the
* In 1751, on the 26th of May, a mass of iron fell to the
earth at Agram in Croatia, at six o'clock in the evening ; at
Lahore in Hindostan, the 17th of April 1621; in Lucania, fifty-
two or fifty-six years before the Christian era; and we have
many authentic accounts of the fall of meteoric stones of various
sizes, sometimes singly, sometimes in showers, which all contain
nickeliferous iron.
E 5
82 THE ENGINEER'S MANUAL
Cape of Good Hope, and many more, in various
parts of the globe, we have no account beyond a
description of their size and general appearance,
which is that of an irregular mass of iron, much
corroded and oxidated by exposure to the air. They
are quite malleable when nearly pure ; but all
meteoric iron contains a proportion of nickel, which
is sometimes sufficient to render it rather brittle,
Infusible by the blowpipe. Specific gravity, 6'4 to
7-8.
The ores of iron are: —
Alloys : Carbonate.
Native iron. Sulphate.
Sulphurets. Chromate.
Oxides. Phosphate.
Hydrate. Arseniate
SULPHURETS.
IRON PYRITEs (Martial Pyrites; Marcassite;)
Is of a pale golden yellow colour, but much less
bright than copper pyrites. It is sometimes massive,
forming considerable veins, and very frequently
crystallised. Its crystals belong to the cubic system,
and it is one of the few minerals which assume the
OF MINERALOGY. 83
forms of the pentagonaldodecahedron” and icosahedron
(figs. 4, 5.): octahedral crystals are not very common.
The cubes of iron pyrites, and other substances which
crystallise in these forms, are often striated in a
peculiar manner, parallel to those edges of the dodeca-
hedron which lie in the same directions (fig. 18.). i. It
is considerably harder than copper pyrites; is scratched
with some difficulty by a knife, and will strike fire
with steel. It is of such universal occurrence, that
to particularise its localities or the different strata in
which it is found abundantly, would be, in the first
case impossible, and in the last needless. It is not
made use of, as other ores of iron, for the purpose of
smelting; but is either decomposed by exposure to
the atmosphere and moisture, and thus converted
into sulphate (green vitriol), or the sulphur is ob-
tained from it by means of heat.
The nodules of iron pyrites, which are abundant in
the chalk strata, consist of fibres radiating from the
centre; the exterior is often deep brown, and when
* It must be observed that the dodecahedron of iron pyrites
differs a little in its angles from the regular one, which is classed
among the platonic solids.
f The references to figures, from this page to the end of the
work, refer to Plate III., except fig. 19. in p. 100., and fig. 20.
p. 107., which refer to Plate II.
E 6
84 THE ENGINEER'S MANUAL
broken exhibits an earthy texture, the result of
decomposition: sometimes the points of Octobedral
crystals appear on the surface.
MAGNETIC PYRITEs. (Hepatic Pyrites.)
This is a much scarcer mineral than the preceding.
It contains a smaller proportion of sulphur than the
common iron pyrites, and affects the magnetic needle.
The colour is a reddish bronze, with a metallic lustre,
and when crystallised it takes the form of an hexagonal
prism, of which the terminal edges or angles are
generally truncated. (fig. 15.)
ARSENICAL IRON PYRITES. (Arsenical Iron ;
Mispikel.)
The arsenical pyrites occurs in many of the localities
of tin ore, both in Cornwall and other countries.
Unfortunately, it is altogether unprofitable ; and we
describe it, that it may not be mistaken for any other
substance, as it is always carefully separated from the
ores with which it is found, before they are smelted.
Its colour is white, or yellowish white, sometimes
inclining to grey; the lustre metallic; and it is either
disseminated in small masses, or crystallised in short
OF MINERALOGY. 85
rhombic prisms, variously modified, chiefly on the
angles. (figs. 38, 39.) Like iron pyrites, it is hard
enough to give sparks with steel; but when struck,
the odour of arsenic is perceptible. Its specific
gravity is 6-1, while that of iron pyrites does not
exceed 5. -
By exposure to the action of the blowpipe we
obtain a metallic globule, which is attractable by the
magnet.
OXIDES.
(MAGNETIC IRON ORE. (Loadstone; Natural Magnet.)
WE are acquainted with but two species of oxide
of iron, though the varieties of one of them (red oxide)
are very numerous, and have at different times been
named as distinct species. The magnetic iron (which
is the least oxidated) is of rare occurrence in Great
Britain. Its colour is dark steel-grey, with a metallic
or semi-metallic lustre; and when crushed, the powder
is nearly black. It forms, in some countries, immense
masses and thick veins, but is sometimes crystallised
in the form of the regular octahedron, the same solid
86 THE ENGINEER'S MANUAL
with its edges replaced, and the rhombohedron (figs. 2.
9, 10.): specific gravity 4-7 to 5. Small crystals have
been found sparingly imbedded in serpentine, in Unst,
one of the Shetland Isles, in some parts of Cornwall
and Devon, and at the gold mines of Wicklow in
Ireland. In the latter place, it occurs in the alluvial
soil; but it is most abundant in the older crystalline
rocks, such as gneiss, and more particularly, mica
schist; and it is much disseminated through the rocks
which consist principally of horblende and serpentine.
No large masses of the magnetic iron ore are known
in England; but in Sweden and Norway, the greater
part of the mountains at Damnemora, Nordmarker,
Arendal, &c. consist of it.
This ore not only affects the magnetic needle, but
is itself magnetic, possessing whether in large or
small masses, a north and south pole ; and it will
retain by attraction objects made of iron and steel.
It is an excellent and profitable ore for smelting,
when found in large quantities, being very free from
extraneous substances; and is said to be more advan-
tageous for the production of steel than of bar iron.
Blende, galena, pyrites, and garnets are often found
with magnetic iron ore; the latter sometimes imbedded
in it.
OF MINERALOGY. 87
RED OxIDE OF IRON. (Perovide of Iron.)
The varieties of this oxide are so different in their
appearance, that at first sight it would appear im-
possible that they should be the same substance,
differing only in their mode of aggregation.
SPECULAR IRON (Iron Glance; Oligiste Iron ;)
Is the red oxide in a pure and crystalline state.
The crystals are black or dark steel-grey externally,
and very splendent; or they have a beautiful iri-
descent tarnish. The most beautiful specimens of
this kind are brought from the Island of Elba, where
there are very extensive and ancient mines of it.
When broken, the colour is dark steel-grey, and the
lustre brilliant ; but when powdered, the colour of all
varieties of this species, whether crystallised or
otherwise, is deep blood-red; and thin fragments or
plates, held between the eye and the light, transmit
the same colour. The crystals are derivable from a
slightly acute rhomboid : some are very complicated,
others are so thin and flat that they resemble scales of
mica. In the latter form, specular iron has been found
in Perthshire, and also near Tavistock in Devonshire.
Some specimens of this ore affect the magnet; but
88 THE ENGINEER'S MANUAL
this character is by no means constant. Specific
gravity about 5.
RED IRONSTONE ; RED HAEMATITE ; RED IRON
OCHRE.
These are all varieties of the same oxide, and are
found in great plenty in several parts of England,
forming large and small veins in the mountain lime-
stone, and, more seldom, thin beds in the same forma-
tion.
Red ironstone is compact, of a colour intermediate
between brick-red and blood-red, opaque and without
lustre: some varieties incline to steel-grey, and these
have a slightly glimmering lustre, as if from an inter-
mixture of metallic powder. Haematite is the same
mineral, with a compactly radiated structure. In this
form it is known to many persons, being used to
make burnishers for polishing the gilding on porcelain
and other substances. Both these kinds are less hard
than the specular or crystallised red oxide, being
scratched without difficulty by a good knife.
With these varieties we often find red ochre, which
is the red oxide of iron intermixed with a considerable
proportion of clay; it is much softer, of lower specific
gravity, and lighter colour. Red chalk is the same
OIF MINEBALOGY. 89
mineral. At Ulverstone in Lancashire all these kinds
of red iron ore, except the specular iron, are found in
a vein of immense thickness, which traverses the
mountain limestone. In Lanarkshire the ironstone
vein intersects a sandstone belonging to the same
formation; near Edinburgh this ore is found in green-
stone, (at Salisbury Crag); and in Cornwall, at
Botallack Mine, near the Land's End, in slate, but not
abundantly. In many other countries it is extensively
worked; more often in the secondary limestone,
(mountain limestone), and other formations of nearly
the same period, but occasionally in older rocks.
These ores may be easily distinguished from the
red silver and red copper ores, by their infusibility
when exposed without addition to the action of the
blowpipe.
HYDRATE OF IRON. (Brown Haºmatite; Brown Iron-
stone; Bog Ore; Morass Ore.)
It is but lately that the brown ironstone and
hasmatite have been worked as iron ore in England,
though in France they have long been smelted in
large quantities. This may perhaps have arisen from
90 THE ENGINEER'S MANUAL
its being found much less abundantly in this country
than other profitable ores. At present, however, in
the eastern part of Cornwall, where it is plentiful, it
is raised for the forge; though formerly it was thrown
aside, as not being worth the process necessary for its
reduction.
The brown haematite resembles the red hasmatite
in its structure, exhibiting, when broken, a radiated
fibrous fracture, but it has a silky lustre. It occurs
in nodules and kidney-form masses; also in stalactites
and tubes, which are found pendent in the cavities of
veins. The general colour is a coffee-brown; but
near the exterior, which is very dark, sometimes
black and shining, there is often a band of a lighter
and yellower colour: sometimes there are two or
three of these bands; and they are always very
parallel, following the undulations of the surface. It
is softer and more brittle than the red hasmatite, and
not quite so heavy.
Brown ironstone bears the same relation to this
mineral that red ironstone does to red haematite. It
is more or less compact, according to its purity, con-
taining sometimes a small proportion of clay and
silex. The powder of both varieties is yellow.
Yellow ochre is another state of hydrate of iron;
OF MINERALOGY. 91
sometimes pure, sometimes combined with alumina
or hydrate of alumina. When free from any inter-
mixture of other substances, it is collected for the
purpose of manufacturing the colour so named. Near
Shotover Hill in Oxfordshire, it is obtained from the
lower bed of the greensand formation, lying under
the lias linestone; and it has been found abundantly
in parts of some of the copper veins in Cornwall.
There are some other varieties of hydrate of iron,
called pea-iron ore (Bohmerz), bog ore, morass ore,
and meadow ore. They are all capable of being
smelted; and in some parts of Europe a good deal of
iron is obtained from them; but in Great Britain
they are found but in few localities, and not very
abundantly. One of the principal depositories in
this country is the morass at the foot of the Cheviot
Hills: they occur also in some parts of the High-
lands of Scotland, in the Shetlands and Orkneys.
Their colour varies from yellowish to blackish-
brown, and the texture from compact to friable, with
a dull earthy fracture. Those varieties which are the
most compact generally contain numerous cavities,
sometimes lined with the same substance in the state
of powder.
The pea-iron ore, which is abundant in the Jura
92 THE ENGINEER'S MANUAL
Mountains and some other parts of the Continent,
consists, as its name implies, of small globular
masses, which are compressed together, and cemented
by the same substance: their texture varies from
compact to earthy or even friable. It contains 30 or
more per cent. of alumina, intermixed with the
hydrate of iron. It forms extensive beds in some
countries.
All the different kinds of hydrate of iron are cha-
racterised by affording water when calcined, and by
their producing, when melted with borax, a dull-green
glass, containing metallic globules, attractable by the
magnet.
CARBON ATES.
CARBONATE of IRON. (Sparry Iron Ore; Brown
Spar ; Clay Iron Ore; Clay Ironstone.)
WHEN pure, carbonate of iron is white, and crys-
tallises in the form of an obtuse rhomb, differing
very slightly from that of carbonate of lime and
some other solids of the rhombic system ; but it pre-
sents few modifications. (figs. 11, 12. 18.) In Corn-
OF MINERALOGY. 93
wall it has been found in hexagonal prisms of a wax-
yellow colour, from half an inch to three quarters in
diameter, and in very obtuse small rhomboids of a
pure white; but in this state it is scarce. A less
pure variety with a lamellar or crystalline structure,
generally of a brown colour, is found in considerable
quantity in some localities, in detached masses, and
filling small veins in various strata, sometimes in the
slates of the primary system, but more often in the
secondary rocks, particularly those belonging to the
coal formation and mountain limestone. This va-
riety, as well as the crystallised carbonate of iron,
very much resembles calc-spar in its external appear-
ance, but it may be distinguished by its greater
weight, (the specific gravity of brown spar is from
3-4 to 3:8, that of calc-spar not more than 2:7,) by its
effervescing more slowly when a drop of hydrochloric
or nitric acid is applied to it, and by the different
results obtained by the blowpipe: calc-spar becomes
perfectly white, being converted into quick lime; but
carbonate of iron blackens, and becomes attractable
by the magnet.
The lamellar variety has long been smelted in
France, though it is by no means plentiful in
England; while, on the other hand, the French have,
94 THE ENGINEER'S MANUAL
until recently, neglected a very useful though less
pure ore, which supplies a great part of the English
furnaces, the
CLAY IRON ORE.
This is the carbonate of iron intermixed with a
considerable proportion of earthy matter, and pre-
senting no outward appearance of being a metallic
mineral, resembling rather an indurated clay of a
dull yellowish-grey colour, sometimes passing to a
dirty brown, or a bluish grey, which is occasionally
very dark. Its texture is earthy, more or less com-
pact, and breaking generally with an even fracture,
which is sometimes slightly conchoidal. Sometimes
it has a slaty structure, which is particularly the case
with the tabular masses. They are occasionally very
large, and lie in a parallel direction one to another,
forming extensive beds between the sandstones of
the coal formation. The nodules also, which are of
various forms and dimensions, are not imbedded in-
discriminately; neither do they fill veins, like other
ores; but clay ironstone seems to form a part of the
system of strata in which it occurs; and where the
bed is not continuous, the interstices are filled with
shale. The nodules are sometimes kidney-shaped,
OF MIN Eſ: A LOGY. 95
sometimes having the form of oblate spheroids; and
they frequently contain impressions of plants, par-
ticularly of reeds and ferns, which are found also in
the sandstones contiguous to them. They sometimes
split readily in the direction of these leaves or
branches, exhibiting an impression on either side.
Petrified shells also are abundant in the clay iron-
stone of some localities; as in some parts of Derby-
shire, where the ore is of a brown colour, and the
shells nearly black.
Clay ironstone is not confined entirely to the
strata of the coal formation; it is found in the
Wealden sand, and considerable quantities are raised
in Sussex.
The composition of clay ironstone varies exceed-
ingly : in some instances it contains sixty per cent.
of carbonate of iron; in others, not more than twenty-
two ; the remainder being a variable mixture of alu-
mina, silica, and the carbonates of lime, magnesia,
and manganese.
SULPHATE OF IRON, (Green Vitriol,)
LIKE Sulphate of copper, is produced by the decom-
position of pyrites, and particularly of the white iron
96 THE ENGINEER'S MANUAL
pyrites. Small quantities of it are found in many of
the localities where that mineral is abundant, either
in small masses, in the form of stalactites, or as an
efflorescence. Its colour is generally green, if the
substance be pure; but in situations where it has
been exposed to the action of the atmosphere it is
often yellow or brownish. It is rarely crystal-
lised, and is seldom found in sufficient quantity
to be collected separately ; but is prepared arti-
ficially from iron pyrites, by causing it to decompose.
It is very soluble, and may easily be recognised by
its metallic and styptic taste.
CHROMITE OF IRON.
From this mineral chromate of potash is manufac-
tured, which is employed in the preparation of chro-
mate of lead, commonly known by the name of
chrome yellow : the chrome green, which is used for
painting on porcelain, is also obtained from it.
Its colour is black, with a metallic lustre; and
when crystallised it takes the form of the regular
octahedron. In these points it has some resemblance
to the native magnetic iron; but the chromite of
iron does not affect the magnetic needle until it has
been exposed to the blowpipe; which, however, does
OF MINERALOGY. 97
not reduce it without addition. When it is melted
with potash, it becomes soluble in water, and the
solution will be of a fine orange colour. It is harder
than glass.
Hitherto this mineral has been found in very small
quantity in the British Isles; and in but few localities,
namely, Portsoy in Banff, and two of the Shetlands,
Unst and Fetlar. In all these places it occurs in
serpentine, its most usual repository in other coun-
tries. It is found in France and several other Eu-
ropean territories, in Siberia, and North America.
PHOSPHATE OF IRON. (Vivianite.)
This is a rare mineral, and has not at present been
applied to any use. In Cornwall and Derbyshire it
occurs in transparent prismatic crystals, of a fine blue
colour, which are sometimes two inches in length,
sometimes very small and slender, forming small
groups in the cavities of pyrites or shale.
ARSENIATE OF IRON.
It occurs in very small cubic crystals of a dark
olive-green colour, with (generally) a shining surface,
attached to brown haematite or the copper ores. It
F
98 THE ENGINEER'S MANUAL
is of no utility, but we mention it on account of its
being associated with other ores, which belong to the
primary and granitic rocks, and of which it may pro-
bably be an indication.
OF MINERALOGY. 99
T I IN,
THE only natural combinations of this metal at
present known, are—the oxide, from which all the tin
of commerce is obtained; and a sulphuret combined
with copper, which has been found in very small
quantity.
TIN PYRITEs. (Sulphuret of Tin ; Bell-metal Ore.)
Colour varying from steel-grey to yellowish or
reddish white; lustre perfectly metallic; fracture
fine granular, sometimes approaching to the con-
choidal form; specific gravity, 4:3 to 47; fusible
by the blowpipe, depositing a white powder on the
charcoal, which is not volatile: this is the oxide of
tin.
In Huel Rock (parish of St. Agnes, Cornwall,)
it was found partially filling a vein of considerable
width, with blende and iron pyrites.
OXIDE OF TIN. (Tin-stone; Stream-tin; PWood-tin.)
It is most usually crystallised or granular; some-
times massive, with numerous small cavities. When
granular, it is much intermixed with the vein-stone,
and the minute crystals are often thickly imbedded
F 2
100 THE ENGINEER'S MANUAL
in it, while the larger ones generally line the cavities
of the veins.
The crystals are square prisms, terminated by
pyramids, of which the edges are often replaced (figs.
27, 28, 29.); but it is seldom that more than one
termination is visible. It presents also other modi-
fications, but they are much less common than these
forms. Maculed or twin crystals (fig. 19.) are also
frequently met with.
The crystals are mostly very small, but they are
occasionally an inch or more in length. Its most
common colour is dark brown, but crystals are some-
times met with yellowish, or even colourless, and
transparent; the darker varieties are semi-transparent,
and the black ones opaque. Externally the crystals
are generally shining; and the lustre of the fracture
is brilliant: when scratched or pulverised, the
powder is white: it is sufficiently hard to give sparks
with steel, but brittle ; and the specific gravity is as
high as 6.5 to 6-9; which is remarkable, being nearly
as great as that of pure tin.
These ores belong to the oldest formations of rocks.
In England the tin veins appear to be confined to
the granite and clay-slate of Cornwall; and in other
countries they traverse the same rocks, and also
OF MINERALOGY. 101
gneiss and mica-slate; but they have rarely been
observed in those strata which are the great reposi-
tories of lead and silver ores. The vein-stones of
tin are generally white quartz and chlorite; and
many other crystallised minerals are found with it,
as fluor-spar, topaz (the latter particularly in Saxony,
and occasionally in Cornwall), schorl, actinolite,
phosphate of lime, iron and copper pyrites, and
blende. It may be observed that the ore of tin is
generally found nearer to the surface of the earth in
Cornwall than the ores of copper.
STREAM-TIN.
In the beds of streams in those countries where
tin veins occur, rolled masses of oxide of tin, and
grains of various sizes, are often found intermixed
with fragments of rock, pebbles, and sand; the
whole rounded by attrition. These are collected for
the purpose of smelting, and the diluvial matter with
which the ore is intermixed is separated from it by
washing in a stream of water, which is made to pass
over it. The places where this operation is performed
are called stream-works, and the ore so collected,
stream-tin. Such deposits are met with, not only in
Cornwall, but in Chili and some other localities. In
F 3
102 THE ENGINEER'S MANUAL
these situations grains of native gold are generally
found intermixed with the tin ore; and small quan-
tities of granular tin-stone have been observed
amongst the alluvial gold of Wicklow.
WOOD-TIN.
This is a fibrous variety of the same substance,
which occurs in the form of pebbles, and reniform or
somewhat globular masses of rather a larger size, in
the stream works of Cornwall. It is very similar,
both in its colour and structure, to the brown haema-
tite, having internally the same radiated fibrous
appearance, though more compact, and with less
lustre, and the same concentric shades of dark and
yellowish brown. Wherever these two varieties may
be observed, it will be well to explore the neighbour-
ing rocks from which the stream descends, as it is
probable that tin veins will be discovered at no great
distance.
The granite and slate of Cornwall contain one of
the greatest known deposits of tin ore, which has
been explored from a very early period. A great
part of the armour of the ancient Greeks, which was
a compound of tin and copper, was fabricated with
the tin of Cornwall. No tin-stone, however, has yet
been observed in the granite of Scotland.
OF MINERALOGY. 103
LEAD,
THERE are many natural combinations of this metal,
and a great part of them are found in Great Britain;
but one only is principally used as an ore for smelt-
ing — the sulphuret, or galena. We say principally,
because the carbonate and other combinations often
occur in small quantity with it, and are not rejected.
The following table exhibits its various ores: —
Alloy : Chloride:
Native lead. Corneous lead ore.
Sulphuret: Carbonate.
Galena. Sulphato-carbonate.
argentiferous Sulphate.
— antimonial. Phosphate.
Oxides : Arseniate.
Yellow oxide Chromate.
Red oxide. Tungstate.
Molybdate.
NATIVE LEAD.
Has hitherto been found only in small particles
in some of the substances ejected from volcanoes,
and still more rarely, forming slender prisms in
masses of galena. It has all the characters of pure
lead, is very fusible, malleable, soluble in nitric acid,
and on immersing a plate of zinc in the solution, a
F 4
104 THE ENGINEER'S MANUAL
film of lead will be deposited on it; but no precipita-
tion takes place on the immersion of copper, which
distinguishes this metal from silver.
GALENA. (Sulphuret of Lead; Lead Glance.)
This ore is very widely distributed through various
formations, from the oldest of the primary rocks to
the newer secondary ones.
It is a mineral easily recognised, whether crystal-
lised or amorphous: in the former case, it offers some
of the forms belonging to the cubic system ; most
usually, the cube with its angles truncated (figs. 1.6.);
more seldom, the cube with the edges replaced by one
plane (fig. 8.), or by two. (ſig. 8*.)
The crystals are often dull externally; but when
broken, the fracture is very brilliant, with a perfectly
metallic lustre, and the cleavages are always parallel
to the faces of the cube. It is very brittle, so much
so that cleavages may generally be obtained by a
slight blow, or even by dropping a piece on the floor.
The same crystalline structure prevails where there is
no regular external form, as when the galena entirely
fills the vein. But this sort of crystallisation is often
interrupted, so as to produce a sort of granular struc-
ture, similar to that of Parian or Carrara marble :
OF MINERALOGY. 105
occasionally, it is fine-grained, granular and rarely
compact: in the latter variety there is not much
lustre.
The specific gravity of galena is 775; it is easily
fusible by the blowpipe, giving off sulphureous
vapour. Its solution in nitric acid will precipitate a
film of lead on zinc, when immersed in it. If precipi-
tation takes place also on the immersion of copper,
the galena contains a portion of sulphuret of silver :
and if, on exposure to the blowpipe, white vapour is
disengaged, it is evident that some sulphuret of anti-
mony is combined with it.
The vein-stone of galena varies in different loca-
lities, and in the different strata. In Derbyshire,
Leicestershire, and other places, where the lead veins
traverse the mountain limestone, the vein-stone is
generally carbonate of lime or sulphate of baryte,
affording beautiful specimens of calc-spar and fluor-
spar. The metallic minerals, which are most com-
monly associated with it in these veins, are copper
pyrites and blende; sometimes, also, iron pyrites and
carbonate of iron. The crystals occur in the cavities
of the larger veins, and one specimen of moderate
size often exhibits several of the above-named sub-
stances. In Cornwall and Devonshire, where the
F 5
106 THE ENGINEER'S MANUAL
lead veins traverse granite and slate, the galena is
accompanied by quartz and fluor-spar. In the north
of England and the lead mines of Lanarkshire, car-
bonate and sulphate of barytes are the prevailing
vein-stones.
OXIDES OF LEAD.
Both the yellow, or protoxide, and the red, or
peroxide of lead, are very rare in nature: they have
been observed occasionally, in the form of powder, in
some mines, associated with other ores of lead. Both
species are reducible with the greatest ease when
exposed on charcoal to the blowpipe; the latter
would be easily recognised by its well-known colour.
If found in any considerable quantity, they would be
most valuable ores.
CARBONATE OF LEAD. (White Lead Ore.)
When crystallised, this mineral is perfectly trans-
parent, and is remarkable for its great brilliancy,
which, owing to its high refractive power, is equal,
if not superior, to that of the diamond. The crystals
are of very various forms, derivable from a right
rhombic prism (figs. 31, 32, 33.); many of the simple
ones are tabular (fig. 32.), but from the aggregation
OF MINERALOGY. 107
of several, an hexagonal prism results, terminated by
pyramids (fig. 33.), very similar to the common
crystal of quartz (rock crystal); but the hexagonal
base differs from the regular figure, the angles not
being all equal. It occurs also in a columnar or
bacillar form, having a silky lustre, but nearly
opaque, and the fibres are more often parallel than
diverging (Pl. II. fig. 20.); sometimes in acicular
crystals. Copper pyrites and blende are frequently
intermixed with it; and in Cornwall it is associated
with sulphuret of antimony, iron pyrites, and other
ores and minerals peculiar to the rocks of that district.
Sometimes it is massive and crystalline, without
any regular form, breaking either in large flakes or
with a fracture which is either uneven or conchoidal,
but always with a brilliant lustre. In the Durham
and Derbyshire lead mines an earthy variety is
abundant. This kind is somewhat like chalk, but
generally less compact, sometimes even friable, and
often stained with green or reddish-brown, by copper
or oxide of iron.
Carbonate of lead may be distinguished from most
earthy minerals by its great weight, its specific
gravity being 6'7; the only one which is sufficiently
heavy to be at first glance mistaken for it, is the Sul-
F 6
I08 THE ENGINEER'S MANUAL
phate of baryte, or heavy spar, which is very common
in the lead mines of the north of England, Shrop-
shire, and Wales; but they may readily be distin-
guished by the effervescence of carbonate of lead, on
the application of nitric or hydrochloric acid. All the
varieties of this ore are easily reducible by the blow-
pipe to the metallic state; and as they contain above
70 per cent. of pure lead, are very profitable for
Smelting.
The sulphato-carbonate of lead, which very much
resembles the pure carbonate, is a scarce substance,
which has been found crystallised in the mines of the
Lead Hills in Lanarkshire. It effervesces much
more feebly with acids than the carbonate of lead.
SULPHATE OF LEAD (Lead Vitriol)
Generally occurs in small crystals, colourless or
yellowish, transparent or translucent, derived from
a right rhombic prism : more seldom, it is massive,
with a lamellar or crystalline structure, and con-
siderable lustre. It is softer than the carbonate,
and will not effervesce on the application of acid.
It was discovered in the Parys copper mine, Angle-
sea; the crystals attached to a cellular ochrey mineral,
of a dark brown colour.
OF MINERALOGY. 109
PHOSPHATE OF LEAD. (Green Lead Ore.)
This is by no means a common mineral in the
lead mines of Great Britain. It is generally of a
beautiful light warm green colour; sometimes yel-
lowish or brownish ; opaque, or nearly so; and crys-
tallised in six-sided prisms, which are often modified
by small planes on all the edges; sometimes having
pyramidal terminations (figs. 14, 15, 15°.); but they
are mostly very small, or even so minute as to produce
the appearance of moss.
The blowpipe has a very singular effect on this
mineral : it fuses into a dark-coloured globule, which,
on cooling, assumes a polyhedral form : on re-melt-
ing this with borax, small globules of lead will be
perceived in the glass so produced.
ARSENIATE, CHROMATE, TUNGSTATE, MoLYBDATE,
CHLORIDE, OF LEAD.
All these minerals are at present very scarce sub-
stances, valuable merely as cabinet specimens: we
will, however, briefly describe them, as, if they should
hereafter be found abundantly, it is probable that
some at least might be very profitable, especially
the chromate.
I 10 THE ENGINEER'S MANUAL
CHROMATE OF LEAD.
We have already noticed that this substance is
prepared in laboratories with the chromic acid ob-
tained from the chromite of iron, and is of a rich
yellow or orange colour: the natural crystals are
so deep-coloured as to approach to scarlet; but, when
pulverised, the powder is yellow. The crystals are
small rhombic prisms, of which the base is very
nearly a square: these are terminated either by two
or four planes. It has been found hitherto only in
Siberia and Brazil, with galena and quartz, and
sometimes phosphate of lead.
ARSENIATE OF LEAD.
It is of a pale reddish or yellowish brown colour,
and occurs in the form of very small hexagonal
prisms, which appear to consist of silky fibres, fas-
ciculated together; sometimes also it is mammillated
and compact; generally translucent; tender, but
harder than calc-spar; soluble in nitric acid; re-
ducible on charcoal by the blowpipe, giving off
arsenical vapour. Found in some of the Cornish
mines with red oxide and other ores of copper, and
in the Beeralston lead mines, Devonshire.
OF MINERALOGY. 111
TUNGSTATE OF LEAD.
Found hitherto only in Bohemia: its existence
even is said to be doubtful, and that a variety of
the brown phosphate has been mistaken for this
substance.
MOLYBDATE OF LEAD.
This mineral occurs in small crystals, which are
square octahedrons, both acute and obtuse (more
frequently the latter), variously modified (figs. 25,
26.), of the colour of bees' wax, or a paler yellow ;
translucent, soft, and brittle : melted with borax
it forms a brownish globule, and with a larger
quantity, a greenish-blue glass.
CHLORIDE OF LEAD. (Muriate, or Murio-
carbonate of Lead.)
The crystals of this mineral are colourless or yel-
lowish, and transparent, with considerable lustre:
it is soft and sectile, resembling in its texture the
chloride of silver; specific gravity, 6. ; reducible,
with some difficulty, alone by the blowpipe: with
soda it readily affords globules of lead.
112 THE ENGINEER'S MANUAL
In England it has been found in the lead mines
of the Mendip Hills, Somerset; and at Cromford,
near Matlock, accompanied by galena, carbonate of
lead, and fluor.
OF MINERALOGY. 113
ZIN C,
ZINC is not an abundant metal, although one of
its ores (blende), like iron pyrites, is widely dis-
tributed. It has never been met with in the
metallic state, either pure or alloyed with other
metals. Its ores are —
Sulphuret (blende).
Red oxyde.
Carbonate (calamine).
Sulphate (white vitriol).
Silicate (electric calamine).
BLENDE.
In its purest state, blende is of a yellow colour,
with a greenish tinge; but it is generally combined
with more or less sulphuret of iron, which renders
it brown, dark reddish brown, sometimes garnet red,
and even black. The yellow blende is semi-trans-
parent, and, in thin fragments, sometimes quite
transparent ; the darker varieties translucent, or
nearly opaque: when massive it is generally brown.
It has considerable lustre, but not of the metallie
kind, and breaks with very distinct cleavages, pa-
rallel to the faces of the regular octahedron. Some
114 THE ENGINEER'S MANUAL
other cleavages may be obtained, but with less fa-
cility. When crystallised, its most usual form is
the rhombohedron (fig. 9.), which is often modified
by small triangular planes, replacing some of the
angles or edges. The crystals are of various sizes,
from a pin's head to a small nut; and their faces,
especially those of the smaller ones, are frequently
convex, and generally brilliant. Its specific gravity
is 4:16.
Blende is not reducible by simple exposure to the
blowpipe, and is only partially soluble in nitric acid.
When pulverised, and digested in sulphuric acid, a
sulphureous odour is perceptible.
This ore does not, like the sulphurets of lead and
copper, occupy large deposits alone: it is principally
distributed among other ores, particularly those of
lead. In the lead mines of Derbyshire, the north
of England, and Scotland, it is abundant; and we
have already remarked that the specimens affording
crystals of galena are very frequently sprinkled
with those of blende : the massive blende and mas-
sive galena are also much intermixed. It is found
in considerable quantity in some of the tin and
copper veins of Cornwall, whence finely crystallised
specimens have been obtained.
OF MINERALOGY. 115
Formerly blende was thrown aside with the vein-
stone, as an unprofitable mineral, all the zinc of
commerce being obtained from calamine; but, for
several years past, it has been employed advanta-
geously for the same purpose.
RED OXIDE OF ZINC.
A mineral of a ruby-red colour, which occurs inter-
mixed with, and imbedded in the oxidulous iron of
some parts of North America (New Jersey, and
near Sparta). It is massive, granular, or micaceous;
the structure lamellar, and affording cleavages
parallel to the faces of the regular hexagonal prism :
translucent, brittle, easily scratched with a knife;
specific gravity, 5:43; infusible without addition ;
but when mixed with carbonate of soda, it fuses into
a transparent yellow bead. It has not yet been met
with in Great Britain, but would undoubtedly be
a valuable discovery, since it contains 88 per cent. of
oxide of zinc, the remaining 12 per cent, being the
red oxide of manganese.
116 THE ENGINEER's MANUAL
CALAMINE. (Carbonate of Zinc ; Lapis
Calaminaris.)
When pure and crystallised, calamine is colourless
and transparent; but it is frequently tinged with
yellow, brown, or green, by the intermixture of a mi-
nute portion of the carbonate of iron or copper. The
crystals are rhomboids, both obtuse and acute (figs.
11, 12.), and sometimes triangular dodecahedrons.
(fig. 20.) They are generally small, or even minute,
having a shining vitreous lustre, both externally and
internally. It is very little harder than calc-spar,
and may be easily scratched with a knife. Specific
gravity, 3-6 to 4-4.
The crystallised varieties form but a small part
of the calamine which is raised. It is oftener massive,
with a more or less perfectly lamellar structure; or
earthy and opaque, somewhat resembling, excepting
in its less specific gravity, the earthy carbonate of lead.
Sometimes, also, it is compact, forming small distinct
globular and reniform masses, which are translucent,
and break with an uneven or splintery fracture. The
earthy kind often occurs in masses which have a
cellular or corroded appearance. All the varieties
have nearly the same chemical characters, being
OF MINERALOGY. 117
infusible by the blowpipe without addition; but
heated on charcoal, they give a white vapour, which
condenses around the specimen so assayed. Soluble
in nitric acid, with effervescence; the solution
affording a white precipitate on the addition of
ammonia.
There is another species of carbonate, containing
about 20 per cent. of water, which is earthy and
pulverulent; but it has not been ascertained to exist
in England. The water becomes apparent by
calcination: in other characters it resembles the
common calamine.
In England, the greatest depository of calamine is
the Mendip Hills, near Cross in Somersetshire; a
good deal is obtained from Holywell in Flintshire,
where there are also lead mines, and near Castleton
in Derbyshire; near Bristol likewise, and in the lead
mines of Durham, calamine is raised.
In the lead mines, calamine is found filling or
partially filling veins, either alone or intermixed
with galena and other ores of lead. Phosphate of
lead and calamine are not unfrequently met with in
contact: but this mineral forms likewise considerable
beds in the secondary rocks of some countries,
118 THE ENGINEER'S MANUAL
particularly the carboniferous limestone. It is gene-
rally accompanied by the succeeding species.
SILICATE OF ZINC. (Calamine; Electric Calamine;
Siliceous Carbonate of Zinc.)
There is a great similarity in the general ap-
pearance of this mineral and the carbonate of
zinc. It occurs crystallised, compact, lamellar, and
earthy; white or yellowish-white; transparent when
crystallised, opaque when earthy. The crys-
tals are derived from a right rhombic prism; but
being generally very small, and aggregated con-
fusedly together, their form is not readily dis-
tinguishable. Hence the two species have fre-
quently been confounded together; and, probably,
some specimens analysed may have contained both
substances, and occasioned opinion that this was a
siliceous carbonate of zinc. They may, however,
be distinguished, when pure, by the greater hardness
of the silicate, the circumstance of its not effer-
vescing on the application of acid, and more particu-
larly because it becomes electric by friction. It
affords water by calcination, and on exposure to
the blowpipe it swells considerably, but does not
OF MINERALOGY. | 19
melt without the addition of a flux. The solution
in acids is gelatinous, affording a white precipitate
when ammonia is added.
Both species are used indiscriminately for the
production of zinc, and are frequently melted with
copper, without previous reduction, to form hrass.
SULPHATE OF ZINC. (White Vitriol; Zinc Vitriol.)
Like the sulphates of iron and copper, this salt is
produced by the decomposition of the sulphuret. It
is found occasionally, in small quantity, in old mines,
and principally in such parts of the workings as
have been abandoned.
120 THE ENGINEER'S MANUAL
A N TIMONY,
ALTHOUGH this is far from being a very abundant
metal in nature, compared with iron, copper, and
lead, it is of considerable importance in various
manufactures, particularly for the composition of
type metal, and for the preparation of certain me-
dicines; and consequently may be sought for, when
any indications of it are met with, as a substance
well worth the trouble of research.
Its ores are —
Alloys :
Native antimony.
Arsenical antimony.
Sulphurets:
Grey antimony Ore:
Nickeliferous sulphuret.`
Zinkenite,
Jamesonite.
Bournonite.
Oxides :
White oxide of antimony.
Earthy oxide of antimony.
Red antimony ore.
The only one of these species which is at present
found in sufficient abundance to be of any importance,
is the grey antimony, or simple sulphuret.
OF MINERALOGY. 121
NATIVE ANTIMONY
Is a rare mineral, which occurs occasionally with
antimonial and arsenical ores, filling small veins, as
at Dauphiné and the Hartz. It is perfectly metallic,
nearly as white as silver, and cleavable parallel to
the faces of the regular octahedron; but it has not
been observed crystallised. Specific gravity, 6-7:
somewhat sectile and frangible: before the blow-
pipes it melts and gradually evaporates.
The arsenical antimony somewhat resembles the
foregoing mineral, and is equally scarce. It occurs
principally in the same or similar localities. It is
volatilised by exposure to the blowpipe; and the
arsenic is recognisable by its garlicky odour.
GREY ANTIMONY ORE. (Sulphuret of Antimony.)
It is of a dark lead-grey colour, with a metallic or
semi-metallic lustre, crystallising in right rhombic
prisms, of which the angles are 91° 20' and 88° 40' :
but more frequently in forms derived from this
solid. (figs. 36, 37.) The crystals seldom exhibit two
terminations, being usually aggregated in a radiated
form : sometimes they are very slender, acicular,
G
122 THE ENGINEER'S MANUAL
or even capillary, intersecting each other in all
directions; and the surface, which is generally bright,
is sometimes beautifully tarnished, exhibiting the
prismatic colours. When massive, the grey anti-
mony ore has either an imperfectly crystalline or
compact structure. It is soft and in thin laminae,
very flexible. The specific gravity is from 4:3 to 4-6.
Like the two preceeding species, it is entirely volati-
lised by the blowpipe, and with a moderate heat,
giving off abundance of white vapour.
The sulphuret of antimony sometimes entirely
fills the veins in which it occurs; but these are not
in general of great extent. They traverse, in some
countries, granite, gneiss, and mica-schist; but it also
accompanies other ores, as a subordinate matter,
particularly those of silver and of lead. We have
already noticed that in Cornwall it occurs with
the white carbonate of lead; and it is found oc-
casionally with crystals of calc-spar, and with zinc
and copper ores. In Cornwall it is generally met
with in the cross courses, or north and south veins;
not in those which principally afford copper and
tin, running east and west. In Dumfriesshire there
are antimony mines, where the veins traverse transi-
tion rocks.
OF MINERALOGY. 123
NICKELIFEROUS SULPHURET OF ANTIMONY ;
At present a very rare mineral, of a lead-grey
colour, crystallising in the cubic system : specific
gravity, 6'45; fusible by the blowpipe, disen-
gaging abundant antimonial vapours: the solution
in nitric acid, greenish, giving a green precipitate
on the addition of potash or soda.
ZINKENITE: JAMESONITE:
Sulphurets of antimony and lead, differing prin-
cipally in the proportions of the two metals: the
former crystallises in six-sided prisms, but has not
been observed in Great Britain. The latter was
discovered in Cornwall, imperfectly crystallised, and
bearing great resemblance to Bournonite. Fusible
by the blowpipe, depositing a yellow oxide of lead
on the charcoal, and disengaging white antimonial
vapour.
BOURNONITE. (Endellion; Triple Sulphuret.)
This mineral is a combination of the sulphurets
of antimony, lead, and copper. Its crystals, of a
dark-grey colour, are generally very small and
G 2
124 THE ENGINEER'S MANUAL
brilliant, and exhibit several modifications of a
rectangular prism. The blowpipe volatilises the
antimony, produces the yellow oxide of lead, and
finally a globule of metallic copper results.
WHITE OxTDE OF ANTIMONY.
This mineral, which is a pure oxide of antimony,
does not appear to crystallise externally, but has,
when massive, a crystalline structure. It is some-
times yellowish white, and often has a pearly lustre;
soft and extremely tender. Specific gravity, 5-56.
It is fusible even in the flame of a candle, and is
quickly volatilised by the blowpipe.
It is not uncommon to find this species with the
other ores of antimony, but in very small quantity.
EARTHY WHITE ANTIMONY ORE
Is a hydrous oxide, which occurs in an earthy or
pulverulent form, generally coating the surface of the
grey sulphuret. The chemical characters are the
same as of the preceding species, except that this
affords water by being heated.
OF MINEPALOGY. 125
RED ANTIMONY ORE. (Kermes.)
This is a combination of the sulphuret with the
oxide of antimony. Its colour is a brownish or
dark-purplish red; the surface brilliant, but without
metallic lustre. Its usual form is that of acicular
crystals, divergent or interlaced, which appear to
be very slender rhombic prisms. It is very soft
and tender. Specific gravity, 4-6. Being found
sometimes on the surface of the grey sulphuret of
antimony, it would appear to be the result of a
partial decomposition of that mineral. It is met
with also occasionally among ores of arsenic, inter-
mixed with earthy minerals. At present it is a
very scarce mineral, but would be very profitable
if found in sufficient quantity to smelt.
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126 THE ENGINEER'S MANUAL
M A N G A N ESE,
THE ores of this mineral are not numerous, nor are
they generally found in great abundance, although
it is one of the most widely distributed metals in
mature; since, like iron, it enters in small proportion
into the composition of an immense number of
earthy minerals and several metallic ores. The
greater part of the hydrates of iron, and the carbonate
(including the clay ironstone), contain manganese,
either as an oxide or a carbonate : it is met with in
slate, marble, and many crystalline minerals, par-
ticularly mica (one of the constituents of granite),
of which it is generally the colouring-matter.
The only ores of manganese which are employed
in manufactures, are the oxides, which are by far the
most abundant. They are applied to various pur-
poses, particularly the production of the hydrochloric
acid, and in the manufacture of glass, to destroy the
greenish colour which it often has ; but the metal
itself is not obtained from them. This is an operation
of some difficulty, and would be useless, as manganese
absorbs oxygen immediately and rapidly on exposure
OF MINERALOGY. 127
to the atmosphere; thus returning to its natural
State.
Ores of Manganese.
Sulphuret.
Oxides:
Peroxide.
Pyrolusite.
} Grey manganese Ore. yr
Hydrous oxide. Acerdèse.
Deutoxide of manganese. Braunite.
Barytiferous oxide.
Carbonate.
Silicate.
Phosphate.
ALABANDINE. (Sulphuret of Manganese.)
A mineral of a dark grey colour, with a semi-
metallic lustre. It is somewhat brittle; the specific
gravity, 3-95. It occurs in imperfect crystals, or
small masses, having an interrupted crystalline
structure, or coating other substances. After ex-
posing it to the oxidising flame till the sulphur is
evaporated, if it be melted with soda, the result
will be an imperfect glass, of a green colour, which
is soluble in water.
It is at present a rare substance, but has been
observed in some of the Cornish mines.
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128 THE ENGINEER'S MANUAL
GREY OXIDE OF MANGANESE.
Under this name are included two species, ex-
tremely similar in their appearance, but differing
considerably in their properties, the peroxide being
much more profitable than the hydrous oxide,
whether for the production of the hydrochloric acid,
or for the quantity of oxygen which they afford
when heated. They are both, however, frequently
intermixed in nature, and are employed without
distinction.
They occur crystallised in long prisms, generally
of eight sides, terminated either by two or four
planes, which are often aggregated laterally and
deformed by their mutual pressure; or they form
masses of coarse divergent fibres. Some specimens
very much resemble the grey sulphuret of antimony
in the form and aggregation of their crystals,
but their colour is darker, and, of the two species,
the peroxide has a more decidedly metallic lustre
than the other. The grey manganese ores have
also sometimes a granular structure approaching to
compact; such specimens are generally full of small
cavities, in which is an earthy variety of the same
substance, of a brownish or sooty black colour: it
OF MINERALOGY. 129
is extremely soft, soiling the fingers strongly when
touched, and easily reduced to powder. This kind
has been named wad, or black wad ; and occurs
sometimes in considerable quantity, forming separate
and distinct masses in the deposits of grey manga-
nese ore, which are globular or reniform, or resem-
bling fungi, of various sizes.
The specific gravity of the peroxide (the crystal-
line and compact varieties) is 4-8 or 4.9; that of
the hydrous deutoxide, 4:3: the latter is rather the
harder of the two, and will scratch fluor-spar; the
peroxide will scratch calc-spar, but not fluor-spar.
They may further be distinguished by this circum-
stance, that the peroxide (pyrolusite), when crushed
to powder, is black; the hydrous oxide, brown.
It must be observed also, that the crystals of the
peroxide are derived from an oblique, and the hydrous
oxide from a right rhombic prism.
Grey manganese ore has for many years been
obtained in large quantity at Upton Pyne in
Devonshire, where all the varieties above described
are found. The mines are situated in greywacke
slate, which is intersected by large and small veins,
affording, with the manganese, brown haematite.
The ores of iron and manganese have a great affinity,
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130 THE ENGINEER'S MANUAL
and are found combined in the most variable pro-
portions. Thus, the brown haematite generally con-
tains a portion of oxide or hydrate of manganese ;
and when the haematite is black, or nearly so, it will
be found that the quantity of manganese is so great
as to produce a violet tint when fused with borax.
Umber and wad are both compounds of the hydrous
oxides of iron and manganese: in the former the
iron preponderates; in the latter, the manganese.
The grey manganese ores are not confined to
Devonshire. In Cornwall they are found in clay-
slate, at Kingston Down, near Callington; and in the
neighbourhood of Trebartha: they are also raised in
Warwickshire, and the county of Aberdeen, in the
mountain limestone.
BRAUNITE. (Deutoxide of Manganese.)
This species is very different in appearance from
the foregoing ones. Its crystals, which are generally
very small, are square octahedrons, the summits
being occasionally replaced by four additional faces.
Lustre metallic; powder brown; specific gravity,
4.81; scratches felspar, but is scratched by quartz.
Hitherto it has not been observed in England, and
is still a rare mineral in the few localities where it
OF MINEPALOGY. 131
is found. If met with in sufficient quantity, it would
be advantageous for the production of chlorine.
BARYTIFEROUS MANGANESE ORE,
The peroxide of manganese combined with the
earthe baryta. It has a blueish-grey colour, passing
to steel-grey, with a more or less metallic lustre.
It does not crystallise, but forms masses of various
sizes, which are sometimes granular, sometimes
appearing to consist of twisted fibers closely inter-
laced. Specific gravity, 4.4. It is found in some
of the deposits of the peroxide, as at Perigord, where
it is made use of together with the other species.
All these minerals are infusible by the blowpipe
without addition: when melted with borax, or the
glass of borax, they produce an amethyst-coloured
glass. The same tint, which may sometimes be
observed in window glass, is caused by the manga-
nese having been used in too large a proportion, for
the purpose of destroying the greenish colour which
otherwise generally exists in it.
CARBONATE OF MANGANESE. (Diallogite.)
Like the carbonate of iron, this mineral has for
its primary form an obtuse rhomboid. It offers
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132 THE ENGINEER’s MANUAL
occasionally other figures, deviable from this one,
but its crystals are scarce : it is more usually massive
and lamellar; generally of a pale rose colour, but
sometimes yellowish white, or brown. Specific
gravity, 3-2 to 3.59. It effervesces feebly with
nitric acid; and when melted with carbonate of soda,
it produces a frit, or imperfect glass, of a green colour.
It is far from being an abundant mineral, being
found at present in small veins in some few localities
on the Continent, particularly the Hartz Forest,
Kapnic in Hungary, and Transylvania.
SILICATE OF MANGANESE.
This mineral, of which there are several varieties,
varying in the proportions of silica and manganese,
can scarcely with propriety be called an ore of
manganese. The colour of some specimens is a
beautiful rose red, others are yellowish, or grey.
They are sometimes made use of for snuff-boxes
and other ornamental purposes, being very hard,
and not brittle.
OF MINERALOGY. 133
A R S E N I (),
THE ores of arsenic are neither numerous nor abund-
ant, but some of them are pretty widely distributed,
accompanying other metalliferous minerals, particu-
larly the red silver ores and the arseniurets of cobalt
and nickel. They are —
Native arsenic.
Sulphurets:
Red orpiment.
Yellow orpiment.
Oxide of Arsenic.
NATIVE ARSENIC.
When freshly broken arsenic is of a pale lead-
grey colour, or nearly white, with a perfectly me-
tallic lustre; but it tarnishes rapidly by exposure
to the air, and becomes black. It does not crys-
tallise, but forms masses of various sizes, which have
externally a mammillated form, and are often com-
posed of parallel concentric layers. The specific
gravity, when pure, is 8:3; but it varies considerably,
134 THE ENGINEER'S MANUAL
and is sometimes below 6. Fusible and volatile
by the blowpipe, in a closed tube, or on charcoal.
It is not found in sufficient quantity to be col-
lected on its own account, and is generally thrown
aside, being injurious in the smelting of all other
ores. It has not yet been met with in England.
RED ORPIMENT. (Realgar.)
This mineral is of a brilliant crimson colour,
approaching to scarlet, and semi-transparent. Its
crystals, which are sometimes very complex, are
derived from an oblique rhombic prism. They are
not always very brilliant externally ; but, when
broken, the lustre is perfectly vitreous. It is very
soft and fragile; the specific gravity, 3-6 ; and it is
so volatile that, when heated in a closed tube, it
deposits crystals on the interior of the upper part.
These characters will distinguish it from the red
silver ores, for some of which it might possibly be
mistaken, especially when the crystallisation is in-
distinct.
YELLOW ORPIMENT.
A sulphuret of arsenic, containing a larger pro-
portion of sulphur than the preceding. Its colour
OF MINERALOGY. 135
is a bright golden or lemon yellow, without any
metallic brilliancy; but it has a degree of pearly
lustre, which, together with its tendency to split
readily into thin laminae, gives it considerable re-
semblance to talc. Its chemical characters are the
same as those of realgar.
These two substances are employed in painting,
although the red orpiment is not a permanent colour.
Like native arsenic, they occur in veins which afford
the red silver ores, and the ores of lead and cobalt,
but have not hitherto been met with in Great
Britain.
OxIDE OF ARSENIC.
A mineral which occurs but rarely, of a white
colour, and pulverulent. It may be distinguished
from all other metallic minerals which resemble it
in colour and texture, by the strong odour of garlic
which is immediately perceptible when it is heated.
136 THE ENGINEER'S MANUAL
C O B A. L T,
THERE are but few ores of this metal, and two only
are at present sufficiently abundant to be explored
for commercial purposes. They furnish the colour-
ing-matter of smalt, and the blue colour which is
made use of in potteries, glass-staining, &c. They
are found principally in the oldest and crystalline
rocks, such as gneiss.
It does not occur as a native metal, but we are
acquainted with the following combinations: —
Sulphuret of cobalt.
Arsenio-Sulphuret.
Arsenical cobalt.
Sulphate.
Arseniate.
SULPHURET OF COBAL.T.
A metallic mineral of a pale steel-grey colour,
inclining to yellow : when broken it appears to have
a fine granular structure. It has been found in
irregular masses, and sometimes, but rarely, crys-
tallised in regular octahedrons, near Riddarhytten,
in Sweden.
OF MINERALOGY. 137
CoBALT GLANCE. (Silver-white Cobalt ; Bright-
white Cobalt; Cobaltine; Grey Cobalt, in part.)
This ore of cobalt is quite white, with a perfectly
metallic lustre, and considerable brilliancy. It is
generally crystallised, assuming the forms of the
cubic system, and particularly, like iron pyrites, the
pentagonal dodecahedron, the icosahedron, and the
cube and octahedron modified by planes which tend
to produce these solids. Its colour and greater
specific gravity (6:29), however, sufficiently distin-
guish it from pyrites: it is also more brittle.
When exposed to the action of the blowpipe, after
being heated in the oxidating flame, it melts, the
heat disengaging arsenical fumes: the globule, re-
melted with borax, communicates to it an intense
blue colour. The latter character belongs to all the
ores of cobalt ; but, on heating the preceding mi-
neral (sulphuret of cobalt), no arsenical odour is
perceptible.
The largest known depositaries of this ore are
in Norway and Sweden, where it is associated with
copper pyrites in a stratum of gneiss. A consider-
able quantity is raised in both these countries, and it
has been found, but hitherto very sparingly, in some of
138 THE ENGINEER'S MANUAL
the Cornish mines, as in the copper veins of Dolcoath;
in the cross veins of Herland mine, which afford
native silver; and, with bismuth, at Huel Sparnon,
near Redruth : but it has been considered a different
species, in consequence of occurring uncrystallised
in these localities.
SMALTINE. (Tin-white Cobalt; Arsenical Cobalt.)
The colour of this species is not so purely white
as of the preceding ore ; and by exposure to the air
it acquires a slightly reddish tarnish. Its crystal-
lisations belong to the cubic system ; but they are
similar to those of galena, and do not include the
forms of iron pyrites. There is another peculiarity
in the crystals of this mineral, namely, that their
surfaces are generally convex, and intersected by
irregular cracks: it occurs also in small irregular
masses, arborescent, and reticulated. The lustre is
perfectly metallic, and it is hard and brittle. The
chemical characters are the same as of cobalt glance :
both species are partially soluble in nitric acid, and
their solutions are rose-coloured, approaching to
violet: if alkali be added, the smaltine will give a
violet-blue precipitate ; the cobalt glance, one of a
OF MINERALOGY. 139
reddish-brown colour. It must be remembered
that the tin-white cobalt (smaltine) is an arseniuret
of cobalt, and contains no sulphur; whereas cobalt
glance is a combination of cobalt with both arsenic
and sulphur.
OXIDE OF COBAL.T. (Earthy Cobalt ; Perovide
of Cobalt.)
This substance, which is seldom met with in a
state of purity, is black and pulverulent, forming
small masses in the deposits of cobalt glance and
smaltine, or coating these and other ores in the
vicinity. It is oftener intermixed with a large pro-
portion of earthy matter, to which it imparts a dark
brown or blackish colour.
In England it has been found in sandstone, at
Alderley Edge, Cheshire, with copper pyrites: the
same stratum is coloured by it in various parts far-
ther south, and it occurs in some of the Cornish
mines.
Its identity may easily be ascertained by fusion
with borax, as the smallest particle of it will produce
an intensely blue glass; while the black oxide of
copper, which resembles it in appearance, commu-
nicates to the flux a crude green colour.
140 THE ENGINEER'S MANUAL
We mention this mineral (like some others) be-
cause it may be the indication of a deposit of cobalt
glance, or arsenical cobalt, in the vicinity.
SULPHATE OF COBAL.T. (Red Vitriol; Cobalt Vitriol.)
Like the preceding mineral, this may be met
with, and lead to the discovery of more profitable
ores. It is soluble, and exists in the water of some
mines: when solid it forms small stalactites, or
slender divergent crystals, of a dull red colour.
When calcined, it gives off water, and becomes of
a light rose-colour.
ARSENIATE OF COBAL.T. (Cobalt Bloom.)
A mineral of a pale rose-colour, which is found
in very small semi-globular masses, consisting of
delicate fibres, or acicular crystals, generally on the
surface of other ores of cobalt. In Cornwall, it has
been found with arsenical cobalt and copper ores;
in Stirlingshire, in the silver mine at Alva. The
arsenical fumes it emits when heated, and the blue
colour it communicates to any kind of glass, readily
distinguish it.
OF MINERALOGY. 141
BIS MUT H ,
THIS metal is not found abundantly, nor is it ex-
tensively used in arts or manufactures. It is found
native, and mineralised by sulphur, and more rarely,
as an oxide and combined with arsenic. Its ores
are found in the primary strata.
NATIVE BISMUTH.
Of a reddish white colour, perfectly metallic, and
breaking with a bright lamellar fracture, the cleav-
ages parallel to the faces of the regular octahedron.
When not massive, it sometimes offers a leafy or
feathery appearance. Specific gravity, 4:36. It is
extremely fusible, and when melted over charcoal,
deposits on it a yellow oxide.
SULPHURET OF BISMUTH.
This also has a perfectly metallic lustre, but the
colour is pale steel-grey, or yellowish grey. It occurs
in the form of small prismatic and acicular crystals,
or small fibrous masses composed of these needles,
142 THE ENGINEER'S MANUAL
and often much entangled in the earthy minerals
and other ores which accompany it. It is seldom
quite pure, containing generally a small proportion
of lead or copper, or both.
OxIDE OF BISMUTH
Is a white opaque mineral, without metallic
lustre; sometimes it is shining and lamellar, some-
times dull and earthy. Like the native bismuth,
it may be recognised by the yellow colour which
it deposits on charcoal, before it is reduced to the
metallic state.
OF MINERALOGY. 143
MERCURY,
THE ores of this metal have not yet been observed
in Great Britain or Ireland. We shall, however,
describe them, as it is possible they may exist in
these countries, or the reader may explore other
tracts, where there is a stronger probability of
meeting with them. Its ores are —
Alloys:
Native mercury.
Amalgam.
Sulphuret.
Chloruret.
NATIVE MERCURY.
This metal is too well known, and too peculiar in
its appearance, to require description. It does not
occur abundantly in the liquid state, but appears
in the form of globules, of different sizes, on the
exterior of masses of cinnabar, and sometimes fills
cavities in the same ore. It is not always pure,
containing sometimes a small quantity of silver:
144 THE ENGINEER’s MANUAL
when the proportion of this metal amounts to about
one third of the weight of the mass, it becomes
NATIVE AMALGAM. (Argentiferous Mercury.)
Its colour is perfectly silver-white, metallic, but
with little lustre. It is very soft, and may readily
be cut with a knife. It is generally crystallised,
assuming the form of the rhomboidal dodecahedron,
which is often modified by numerous small planes.
It may be easily distinguished from native silver,
by means of the blowpipe. As the mercury is
volatilised, the crystalline form disappears, and after
a short time, a small bead of silver remains.
CINNABAR. (Sulphuret of Mercury; Vermillion.)
This mineral is of various shades of crimsom red :
the light-coloured varieties are slightly transparent,
with a vitreous lustre, and granular structure; while
the darker specimens incline to steel grey, with a
semi-metallic appearance. When scratched, the
streak is bright scarlet. It occurs in considerable
masses, furnishing, together with the native mercury,
all the quicksilver used in the arts and manufactures :
sometimes, but more rarely, it is crystallised, in
forms derived from an acute rhomboid (fig. 20.). Its
OF MINERALOGY. 145
specific gravity is 8'09, considerably higher than
that of the red silver ores; and it is completely
volatilisable by heat, the whole gradually disappear-
ing, with a sulphureous odour. Cinnabar is some-
times rendered impure by an intermixture of car-
bonaceous matter; and it then has a darker grey
colour, with a tinge of crimson, and scarcely any
lustre. This intermixture arises from its occurring
in the sandstone and shale of the coal formation, in
which, in some countries, it exists in large quantity.
It is found also in the limestone of the same system;
and, less frequently, in clay-slate, as in Hungary.
The great quicksilver mines of Idria in Carniola,
and Almaden in Spain, are situated in the coal
formation.
146 THE ENGINEER's MANUAL
PLATIN A,
THIS metal, which is intermediate in colour between
steel and silver, occurs only in the metallic state,
seldom pure, but alloyed with a small quantity of
iridium, rhodium, palladium, osmium, and sometimes
gold. It is found in small irregular grains, from the
size of sand to that of a pea, very rarely in large,
masses. Its weight is greater than that of any
other metal: in the native state, its specific gravity
is about 17. It is insoluble except in nitro-hydro-
chloric acid, and infusible by the blowpipe. It is
found generally in the deposits of gold-sand, inter-
mixed with grains of zircon, spinel ruby, magnetic
iron, &c. It has been observed also in some auri-
ferous veins in South America, but still in a granular
form; and, within a few years, it has been obtained
from the western side of the Oural Mountains,
accompanied by gold.
OF MINERALOGY. 147
MIN ERAL ROCKS AND EARTHS,
HAVING described all the ores which are at present
made use of, either for reducing them to a metallic
state, or for other purposes, and many other metal-
liferous minerals of which it may be useful to have
some knowledge, we shall give some account of a
few earthy substances, which are met with abundantly
or frequently in the same localities, either as vein-
stones or as constituents of the rocks and strata
to which we have adverted in the former part of
this work.
QUARTz. (Rock Crystal; Amethyst; Fat Quartz.)
Under the name of rock crystal, this substance, in
its purest state, is familiar to most persons; but the
massive quartz which partially fills the metallic
veins of Cornwall and other mining districts has
in general but little transparency. It is mostly
white, with a fatty lustre, which has obtained for it
the denomination of fat quartz ; or tinged with green
and brown, by the oxide of iron or the copper ores
intermixed with it.
H 2
148 THE ENGINEER'S MANUAL
Crystals of quartz, however, or rock crystals, are
by no means uncommon in the cavities of these
veins; their most usual form is an hexagonal prism,
terminated by an hexagonal pyramid (fig. 15.); less
frequently both ends are pyramidal. In granite,
Quartz generally appears in the form of grains, which
are more or less transparent, colourless or greyish.
In the cavities of granite, fine groups of crystals
are sometimes met with, as the brown rock crystals
of Cairn Gorm in Scotland. Amethyst is quartz,
coloured by a small portion of the peroxide of
manganese. But in all these varieties, quartz pre-
serves the same degree of hardness, which is con-
siderably greater than that of glass, and, when
broken, presents always a conchoidal fracture and
vitreous lustre. Sand and sandstone are but modifi-
cations of the same substance (the earth silica),
generally much coloured by the hydrate and oxide of
iron. Flint also is quartz, with a different texture.
The specific gravity of all these varieties is about
2.6; they are unalterable by acids, and infusible by
the blowpipe alone; but when melted with potash
or soda, they form glass. It may be remarked also,
that if two pieces of quartz, of any kind whatever,
be rubbed together, they emit a peculiar and some-
OF MINIERALOGY. 149
what disagreeable smell, and in the dark a faint
phosphorescent light is perceptible.
FELSPAR. (Adularia.)
A crystalline mineral of a greyish white or flesh-
red colour; sometimes also white and yellowish
white; generally opaque or slightly translucent; but
in some kinds of porphyry the crystals of felspar
are perfectly transparent and colourless.
Its crystals, which are sometimes very complex,
are derived from an oblique rhombic prism : and
whether crystallised or massive, except in the compact
variety, felspar presents a crystalline or lamellar
structure, in which two cleavages” are very distinct.
When it is compact, the fracture is either fine
granular or conchoidal, without any lustre. In this
state it forms the base of most porphyries.
The hardness of felspar is much less than that
of quartz, but yet considerably greater than that of
glass: the blowpipe fuses it into a white enamel,
insoluble in all acids; specific gravity, 2-4 to 2:58.
* One parallel to the bases of the primary crystal; the other,
perpendicular to it, is parallel to a plane passing through the
lesser diagonal of the bases.
H 3
150 THE ENGINEER’s MANUAL
CALCSPAR.
This is one of the many varieties of carbonate of
lime ; a species which includes all kinds of limestone,
calcareous marble" chalk, and some other minerals,
which it is not within our province to describe.
Calcspar is generally transparent, or nearly so, and
either colourless or yellowish : sometimes, however, it
has a red or brown colour communicated to it by the
oxides of iron and manganese. The massive calc-
spar which occurs as a veinstone with metalliferous
minerals, is generally white or brownish, and nearly
opaque ; affording with great ease three bright
cleavages, which indicate an obtuse rhomboid as its
primary form. (fig. 11.) It exhibits, perhaps, more
variety of crystallisation than any other mineral. (figs.
12, 13. 18, 19, 20, 21, 22, 23.) The scalene dodeca-
hedron, both more obtuse and more acute than fig. 20.,
occurs in combination with the six-sided prism and
the planes of various rhombs of different degrees of
obtuseness.
Marble is the same substance wherein the crystal-
* Or true marbles; because some kinds of serpentine, which
as a magnesian mineral, have been erroneously called marble.
OF MINERALOGY. 151
line structure is interrupted, and it is granular; but
still showing the bright cleavage surfaces in each
grain: limestone is still more compact.
All the different kinds of carbonate of lime effer-
vesce briskly when acids are applied to them; and
when subjected to a sufficient heat, they become
caustic lime.
FLUORSPAR. (Fluor; Fluate of Lime.)
This mineral, though much less abundant than
the last, is very widely distributed in nature, and
fills the greater part of the metalliferous veins in
several localities. Its colours are various, and ge-
nerally bright: in Durham and Yorkshire, it is most
frequently violet, with a tint of pale green in the
crystals, which are transparent; in Derbyshire, the
most common colours are violet and dark indigo
blue, and fine specimens have been obtained of a
bright yellow colour: sometimes it is limpid, and
more rarely pale rose-colour. It is generally trans-
parent, unless where the colour is very dark; and
frequently enclosing crystals and small particles of
copper pyrites, a mineral with which it is almost con-
stantly associated. In some parts of Cornwall, bright
green fluor is the veinstone of several copper-mines.
H 4
152 THE ENGINEER'S MANUAL
Its crystals are generally cubic, or the edges of
the cube are replaced by two planes; and very often
each face is surmounted by a very flat pyramid (fig.
8 *): the primary form is the regular octahedron,
which however seldom occurs; but the cleavages
are generally evident on the surface of the crystals,
and are easily obtained. In Derbyshire, fluor
occurs with a coarse fibrous structure, of various
shades of blue and purple, very much resembling
amethyst : it forms modules, of different sizes and
and forms, in the veins of sulphate of baryte which
traverse the mountain limestone.
Fluor is harder than calcspar, but may readily be.
scratched by glass or steel. Most varieties become
phosphorescent when heated.
Copper pyrites, Galena, Blende, and Calamine
are the ores most usually met with in the localities
of fluor.
Gypsum. (Selenite; Plaster-stone; Alabaster;
Sulphate of Lime.)
Alabaster, a granular variety of this mineral, is
well known as the material of which vases, small
statues, and other ornamental objects, are formed.
The crystallised varieties are called selenite. The
OF MINERALOGY, 15
crystals are generally colourless and transparent,
with a strong tendency to split in one direction only,
and a somewhat pearly lustre; very rarely it is com-
pact. All the varieties are extremely soft, in most
cases yielding to the pressure of the nail. The gra-
nular kind is massive, and is generally associated
with beds of rock-salt, both in Cheshire and various
parts of the Continent; the two substances forming
considerable deposits in strata of clay. In Cheshire
and Somerset it is generally of a flesh-red colour;
and in other localities it is often grey or bluish.
When calcined, it becomes plaster of Paris, and may
be recognised by its solidifying when mixed with
Water.
CARBONATE OF BARYTE. (Witherite.)
The carbonate and sulphate of baryte are the
heaviest of the earthy minerals, a circumstance which
has caused them to be mistaken for the ores of
metals.
Carbonate of baryte is rarely crystallised; but is
massive, filling veins of considerable width, and,
when broken, very much resembling alum in its
appearance. It is found also in large globular or
spheroidal masses, having a coarsely radiated structure.
H 5
154 THE ENGINEER's MANUAL
In hardness, it is intermediate between calcspar and
fluor; the specific gravity, 4-3. It effervesces with
acids, but much more feebly than carbonate of lime;
and when powdered and thrown on hot coals, it is
slightly phosporescent. By calcination it becomes
caustic, and soluble in acids.
Galena more frequently accompanies the carbonate
of baryte than any other ore; and as a veinstone it
is more abundant in England than any other country.
HEAVY-SPAR. (Sulphate of Baryte.)
Unlike the carbonate of baryte, this mineral is
almost constantly crystallised, or crystalline in its
structure. It is very brittle, a slight blow affording
brilliant cleavages, parallel to its primary form, a
right rhombic prism. The crystals are often tabular,
and exhibit but little of the primary faces. (figs. 32.
35. 39.) They are generally transparent, colourless, or
tinged with brown, seldomer with red or dark grey.
It is about as hard as carbonate of baryte, and rather
heavier.
Sometimes it occurs in small columnar masses,
or bundles of fibers, strongly resembling the carbo-
nate of lead; sometimes a divergent radiated struc-
OF MINERALOGY. 155
ture. This kind is often brown, with a resinous
lustre. It is also met with granular, resembling
marble; and occasionally, as in Derbyshire, earthy
and opaque.
Heavy-spar does not effervesce with acids; is
partially soluble in nitric acid; and is fusible, with
some difficulty, into a white enamel. The ores most
usually accompanied by heavy-spar are those of lead,
silver, and mercury.
CHLORITE.
A mineral of a dark green and sometimes blackish
green colour, generally having an earthy texture,
more or less indurated, or appearing to consist of
minute scales: these scales are crystalline plates,
resembling talc, but they are rarely of such a size
as to allow their form to be distinguished. When
perfect, they appear to be hexagonal plates. It is
extremely soft and tender.
Chlorite is one of the minerals which often ac-
companies metallic ores in the primary strata. In
Cornwall it occurs in most of the tin and copper
veins, but rarely in those which contain lead ore.
156 THE ENGINEER's MANUAL
t ,
S2'
PHYSICAL CHARACTERS
Of
MIN E R A LS,
ALTHOUGH it is not intended to give the reader an
elaborate treatise on the physical characters of mine-
rals, yet, as in the description of ores and other
substances, these characters or qualities are neces-
sarily adverted to, as descriptive of the different
species, it is well that any one, whose occupation
may lead him to investigate the riches of the mineral
kingdom, should have some acquaintance with them,
and also with the terms by which they are some-
times, it may be said, technically described, both in
this and other works on mineralogy. It has been
thought more advisable to devote a few pages to the
explanation of such terms, than to repeated length-
ened descriptions in the body of the work, in order
to avoid the use of them.
In all minerals several of these characters are
observable ; such as form, colour, weight, transpa-
rency, or opacity, &c. They are all included in the
;
4. &
- i - g
a OF MINERALOGY. 157
following table, where, for the sake of greater facility
in referring to them, they are placed in alphabetical
order: —
Adhesiveness to the tongue. Hardness.
Colour. Lustre.
Double Refraction. Magnetism.
Electricity. Odour.
Flexibility. Phosphorescence.
Elasticity. Specific Gravity.
Form : Structure.
Regular or crystalline, Taste.
Irregular. Touch.
Fracture. Transparency.
Frangibility.
Tenacity.
ADHESIVENESS TO THE TONGUE.
A character belonging to but few minerals, and
which arises from their disposition to imbibe mois-
ture rapidly. They are mostly in a state of de-
composition.
COLOUR.
The colours of minerals are often characteristic of
them ; but they also frequently arise from an inter-
mixture of some other substance, which is not essen-
tial to their composition. In the latter case, the
same species often occurs of very different colours,
*S quartz, which when perfectly pure is colourless,
158 THE ENGINEER'S MANUAL
but is sometimes purple, (amethyst); sometimes yel-
low, (Brazilian topaz); or brown, (Cairngorm
stone), &c. On the other hand, cinnabar is always
of a bright crimson colour, unless rendered dark and
dull by some impurity: in carbonate of copper, one
species is deep blue, the other of a brilliant green
colour. Some ores, which are of an iron or lead-grey
colour, exhibit occasionally on their surface brilliant
prismatic colours, which may be considered acci-
dental, and may be easily removed.
DOUBLE REFRACTION.
The transparent variety of calc-spar, commonly
called Iceland spar, is well known to many persons,
as possessing in a strong degree the property of
double refraction. A fragment placed on a written
or printed word, will give the appearance of its
being written or printed twice over, the distance
between the two images depending on the thickness
of the fragment through which it is viewed. For a
long time it was supposed to be a property peculiar
to this substance, which obtained the name of double-
refracting spar; but optical researches, particularly
those regarding the polarisation of light, have proved
that it belongs to all crystallised transparent mine-
OF MINERALOGY. 1.59
rals, except those which assume the forms belonging
to the cubic series. (See Crystalline Form.) In the
greater number, however, it is not immediately per-
ceptible, being very feeble, compared with that of
carbonate of lime.
ELECTRICITY.
The power of exciting electricity by friction has
been known for ages to exist in amber.” There are
many other minerals which have the same property,
but in some few it may be excited by simply warm-
ing them over the flame of a candle; as, for example,
electric calamine.
FLEXIIBILITY.
Most of the native metals, and some few other
substances, are so flexible as to bend by gentle pres-
sure in various directions, but they are not generally
elastic. There are some minerals, however, which
are not only flexible, but elastic, as mica; and this
property will generally distinguish it from talc,
which is only flexible.
* Electrum of the ancients; whence the name electricity.
160 THE ENGINEER'S MANUAL
FORM.
When minerals occur in a definite form, whether
crystallised or otherwise, it is desirable to notice it.
In some cases they cannot be said to possess any
positive external form; as when they entirely fill a
vein, and are massive, the mass being bounded only
by the walls or sides of the vein. But the same
substance often appears, under other circumstances,
either crystallised or in detached masses, having a
form which is peculiar to them. Thus, radiated iron
pyrites and hamatite are generally found in nodules
which are somewhat globular, or reniform (kidney-
shaped). Other minerals have a resemblance to part
of a bunch of grapes closely pressed together, and
are termed botryoidal, as the radiated sulphate of
barytes, phillipsite, &c.; when the spherical portions
of the surface are larger, the form is termed
mammilated.
Arborescent, dendritic, ramose, are applied to the
branched and leafy forms and moss-like aggrega-
tions of crystals, so constantly met with in some of
the native metals, particularly copper and silver.
CRYSTALLISATION, or regular external form, is
*;
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OF MINERALOGY. 161
one of the most important characters of minerals,
inasmuch as it is unvarying in each species.
On looking at a collection of crystallised minerals,
we perceive a number of symmetrical solids; such as
cubes, octahedrons, and prisms, both right and
oblique, and a number of other figures, in which we
trace the planes of these as the fundamental forms,
but which exhibit also a number of additional planes
on their angles or edges; for example, in fig. 8.,
where the general form of a cube is apparent; but,
instead of the original edges, we perceive narrow
planes which replace them : again, in fig. 18., we
See an hexagonal prism, but not a perfect one; three
edges of the upper and three alternate edges of the
lower base being replaced by oblique planes.
Fig. 20., a crystal of common occurrence, may not,
on a first inspection, appear to have any relation to
either of these two solids; and figs. 4. and 5. cer-
tainly do not exhibit any resemblance to a cube;
yet the two latter, as well as figs, 2, 3. 6, 7, 8,
8*, 9, and 10., form part of the cubic series.
It would require the reader to enter too much into
the details of crystallography, to explain the transi-
tion of all these solids one into another: it will be
sufficient to observe, that the triangular planes of
162 THE ENGINEER’s MANUAL
Jig. 6. if extended so as to efface those of the cube,
would produce the regular octahedron (fig. 2.); that
the faces which replace the edges of the cube
(fig. 8."), and of the octahedron (fig. 10.), are com-
pleted in fig. 9., and in both cases produce a solid of
12 sides, called the rhomboidal dodecahedron; and
that the planes of fig. 5. (the icosahedron) are those
of fig. 4. and fig. 2.
In like manner figs. 18. and 20. are referable to
the series belonging to the rhomboid.
The modern system of crystallography, founded
partly on the phenomena of double refraction, has
greatly simplified the relations of the almost endless
variety of natural crystals, by establishing six simple
solids as the types or bases of so many different
systems of symmetrical forms. These are, —
1. The cube (figs. I. to 10.), e.v., native gold,
silver, copper; sulphuret of lead ; fluor-spar; rock-
salt, &c.
2. The rhomboid (figs. 11. to 23.), ea., red sulphu-
ret of silver; cinnabar; carbonate of iron, of mag-
nesia, of lime, &c.
3. The right square prism (figs. 24. to 29.), ex.,
oxide of tin.
4. Right rectangular prism (figs, 30. to 39.), ew.,
OF MINERALOGY. 163
carbonate of lead; sulphuret of antimony; heavy-
Spar.
Note.—This series includes all right prisms which
have a rhombic base.
5. Oblique rhombic prism (figs. 40, and 41.), er-,
blue carbonate of copper.
6. Doubly oblique rhombic prism ; an oblique
prism, of which the base is an oblique-angled paral-
lellogram; the lateral planes inclining unequally on
the base.
It will be seen that the rhomboidal series includes
all right prisms of which the base is the regular
hexagon, or a figure of 12, 18, or 24 sides; and all
the triangular dodecahedrons: some of these are
regular (fig. 15.”), others are formed by twelve sca-
lene triangles. (fig. 20.)
In the square-prism series we find a variety of oc-
tahedrons, acute and obtuse ; and prisms of 4, 8, and
12 sides, with or without pyramidal terminations.
In the next series there is less symmetry; for the
lateral faces of the square prism being all equal, and
similarly situated, they are all similarly affected by
any modification; but in rectangular and rhombic
prisms, only the edges or angles diametrically oppo-
site can be modified in the same manner.
164 THE ENGINEER'S MANUAL
Although the solids of every series may be derived
from, or traced to, its fundamental figure, yet this is
not the primary form of all substances which crys-
tallise in the solids of that series. Thus, fluor-spar
is most frequently met with in cubic crystals, or
cubes slightly modified: octahedral crystals of the
same substance are comparatively rare; yet the
octahedron is termed its primary form, because its
structure exhibits a natural tendency to divide into
such solids, and it is impossible to obtain from it a
cube by mechanical division. This tendency to
divide in certain directions only, affording regular
solids with fixed angles, is called cleavage.
It must here be observed, that crystals, both large
and small, often appear irregular, from the circum-
tance of some of their planes being larger, and some
smaller, than others, which in a state of perfect regu-
larity would be equal: but it will be found that
their inclinations to each other are still the same.
ERACTURE.
The manner in which minerals break, deserves
attention, as the form of the broken surface varies
with their texture or structure. In many crystallised
substances the structure is manifested in the dispo-
OF MINERALOGY. 1.65
sition to break in parallel planes or cleavages; in
others, as rock-crystal, the fracture resembles that of
glass, presenting curved and somewhat spherical
surfaces, meeting at various angles: this is called a
conchoidal fracture: common flint, and most sub-
stances which have a very compact texture, break
with a fracture of this kind. In pyrites we have
an uneven fracture, that is to say, an uneven surface,
which is neither conchoidal nor crystalline. In
other minerals the fracture, in consequence of the
structure, is fibrous or radiated. The kind of lustre
in the fracture likewise varies, and should be ob-
served.
FRANGIBILITY.
The ease with which a mineral may be broken, as
contrasted with its tenacity or toughness. This pro-
perty has little relation to their hardness, many hard
minerals being very brittle, and some very soft ones
difficult to break. The hardness of quartz and of
flint are about equal: and analysis discovers scarcely
1 per cent. of foreign matter in the latter substance;
yet it is much more tenacious than quartz.
HARDNESS.
This property is ascertained by the ease or dif-
ficulty with which a mineral will scratch, or may be
I66 THE ENGINEER'S MANUAL
scratched by another. The greater number of mi-
nerals are much less hard than quartz. This sub-
stance, with felspar, fluor-spar, and carbonate of lime,
are useful standard points, forming a sort of scale,
with which to compare others.
LUSTRE.
Not only the degree, but the kind, of lustre of
minerals should be observed, both externally and
internally. Some are extremely brilliant, as the
carbonate of lead; others moderately so, or bright;
some glimmering, and others quite dull. In the
varieties of lustre, we observe the adamantine, the
vitreous, the resinous, metallic, semi-metallic, pearly,
and silky: the latter is confined chiefly to such as
have a fibrous structure.
MAGNETISM.
It is scarcely necessary to advert to this property
in the oxidulous iron; but it is not so generally
known that the metals cobalt and nickel are slightly
attractable by the magnet.
ODOUR.
There are few minerals which are distinguishable
by their odour. In the natural bitumen, and such as
OF MINERALOGY. 167
contain this matter, it is very evident. Arsenic,
and in Some cases sulphur, are perceptible when the
substances which contain them are thrown on hot
coals, or exposed to the blowpipe.
PHOSPEIORESCENCE.
This property is confined to a small number of
minerals: it is perceptible when they are heated, as
in most varieties of fluor and some kinds of heavy
spar, and of carbonate of lime.
SPECIFIC GRAVITY.
It is not possible to ascertain exactly the specific
gravity or weight of a mineral, as compared with that
of water, without the operations of weighing and
calculating; but in masses of a tolerable size, habit
will enable us to judge in some degree from this
character, when it is considered in addition to others.
STRUCTURE.
We have already adverted to the structure of
minerals, in speaking of their crystallisation and
fracture: we may add, that a peculiar glisten may be
remarked in some minerals, in consequence of their
168 THE ENGINEER’s MANUAL
tendency to cleave in one direction more readily than
in others; and that what is called a foliated structure
is apparent in mica, talc, and yellow orpiment,
where only one cleavage is attainable.
TASTE.
Such minerals as are soluble (common salt and the
metallic sulphates) are recognisable by their taste,
but they are very few.
TOUCH.
Some minerals are distinctly colder to the touch
than others: topaz, for example, is colder than
quartz; the latter, again, is colder than glass. Some
appear soapy or unctuous to the touch ; they gene-
rally contain magnesia: others feel harsh and gritty.
TRANSPARENCY.
When a mineral is not perfectly transparent, it is
perhaps semi-transparent ; or if in a less degree
still, translucent, or translucent only on the edges.
The want of transparency arises in many cases from
the intermixture of colouring matter which is not
chemically combined, as in agates, where the red
and yellow colour arise from oxide and hydrate
of iron.
IND EX.
Page
Acids, use of, in examining
minerals º º - 42
Adhesiveness - * - 157
Alum-slate wº- & – 29
Amalgam - * - 144
Amethyst ass * - 148
Antimony, native - - 121
, sulphuret - id.
, oxide * - 194
, oxide, red - 1:25
Arsenic, native * - 133
, sulphurets - - 134
, oxide - * - 135
Arsenical pyrites - - 84
silver ore - - 53
Barytes, carbonate - - 153
, sulphate * - 154
Basalt - sº & - 15
Bismuth, native * - 141
, sulphuret - - 141
, oxide - wº - 142
Bituminous shale - – 29
Blende - º * - 1 13
Blowpipe & $º - 39
Bog, iron-ore - Aºs - 91
Calamine * tº- - I 16
, electric º - I 18
Calcspar - * tº - 150
Carboniferous system - 22
Chalk - s sº 6, 31
Chalk-marl tº - 31
Page
Chemical characters of mi-
nerals sº wº - 38
Chlorite - tº tº - 155
Cinnabar - tºº 3- - 144
Clay, London - łº - 32
, plastic - sº - id.
—, pipe º * - id.
, weald - sº - 30
Clay iron ore - wº - 94.
Clay slate gº * - 19
Cleavage - * -º * † - 164
Coal measures - * * 7, 24
Cobalt, arsenical * - 138
, sulphuret - - 136
—, glance - * - 137
—, oxide - * = - 139
—, sulphate * - 14O
, arseniate * - id.
Colour - * sº - 157
Copper - tº rº - 62
, native - Eº - 68
—, sulphuret - - 64
—, variegated - - 66
—, pyrites sº - 67
—, grey ore ſº - 68
—, red oxide - - 71
, carbonate, green - 72
, blue - 74
, siliceous 75
—, silicate & 4 - 76
, arseniates - - id.
, sulphate sº - 78
, phosphate - - 79
170
INDEX.
Copper, chloruret -
Cornish mines - º
Cretaceous system -
Cross course - ſº
Crystalline form. -
Dip of strata - º
Double refraction -
Dykes - * *
Earthy minerals s
Effervescence - *
Electricity tº- -
Elvan * *- us
*
External characters of mine-
rals * tº x-
Fault sº tº gº
Felspar - * *-*.
Flexibility * sº
Flint * - * *
, modules in chalk
Fluorspar s *-
Form * sº tºº
Fracture of minerals
Fullers' earth - º
Galena - º sº
Garnet - º gº
Gault *- * *
Gneiss - - sº-
Gold *- sº fº-
Granite - º gº
Greensand tº gº
Greenstone sº &
Greywacke * *
Gypsum - * º
Haematite, red tº-
, brown 3-
, black sº
Hardness of minerals
Heavy-spar - *
*-sºº
26,
*
Page
8O Horneblende *
4 Iron, native - e-
30 , pyrites - *º
12 , magnetic
160 , arsenical
—, magnetic *
1 O , red, oxide -*
158 , red ironstone -
17 —, hydrate - &-
, carbonate *
147 , sulphate - e
42 , chromite *
1.59 —, phosphate *
15 , arseniate - *
37 Killas mº gº sº
17 Lead, native - sº
149 , Sulphuret g-
1.59 —, oxides - cº-
| 48 —, carbonate *
31 —, sulphate - *
151 | —, phosphate cº-
16O —, chromate º
164 —, arseniate - *
3] —, tungstate º
—, molybdate *
104 , chloride - *
14 Lias beds e- º
3] Limestone, mountain
| 8 , SCàr sº
43 , magnesian
13 Lode wº- & sº
31 Lustre of minerals -
I 5
19 Magnesian limestone
152 | Magnetic iron ore -
- Magnetism tºº * -
88 Malachite *-*. sº
89 Manganese ſº *g
130 , sulphuret -
165 *sºmºsºm-º: , oxide *
154 ——, carbonate
Page
14, 15
INDEX.
Page
Manganese, silicate - - 132 Rock crystal -
Marble - * 3- - 150 Rock salt * -
, Purbeck sº – 30 Roestone º
Marl * sº gº - 29
Mercury, native *- - 143 Sand lº s
, argentiferous - 144 | Sandstone &
, Sulphuret - - id. , old red
Metals - *-*. * - 29 , new red
Meteoric stones sº - 8] Selenite - wº-
Mica * x- * 13, 14 Septaria - 3-
Mica schist - * - 18 Serpentine º
Millstone-grit - - - 24 Shale, bituminous
Morass ore º- - - 91 , aluminous
Mountain limestone - - 22 Silver, native -
, auriferous
Odour - -> º - 166 —, antimonial
Oliven ore sº º - 77 , red ore -
Oölite - sº º 6, 28 , sulphuret
Orpiment & - - 134 , chloruret
Slate, clay sº
Pea-iron ore - sº - 91 , mica *-*
Phosphorescence - - 167 || Sparry iron ore
Pipe-clay gº º 32 Specific gravity
Platina - ** º - 146 Stratification -
Porphyry &= tº - 15 Stratified rocks
Primary forms - sº - 164 | Structure *
Primary formations - - 20 Syenite - º:
Pyrites, copper Eº – 67
, iron - sº - 82 Tennantite *
tº, , magnetic - - 84 || Taste - º
, tin - *º - 99 || Tertiary formations
Physical characters of mine- Tile ore - * -
rals. 156 | Tin, sulphuret -
, oxide -
Quartz - {- wº - 147 , wood *
Toadstone *
Red copper ore & - 71 Touch - *
ironstone sº - 88 Transparency -
lead ore - es - 110 | Trap tº *
silver ore - ſº - 53
chalk and red ochre - 88 | Veins - *-
Realgar - sº as: - 134 | Veinstuff - sº
Page
- 148
- 167
- 18
- 167
– 14
- TO
- 16S
- 82
172 INDEX.
Page Page
Wealden formation - - 30 Zinc, red oxide iº - 115
, carbonate ſº - 116
Yellow ochre - tº - 90 , silicate - sº - 118
, sulphate - tº - 1 19
Zinc, sulphuret gºs - 113
THE END,
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