John Pinkerton.

Petralogy. A treatise on rocks (Volume 1) online

. (page 32 of 35)
Online LibraryJohn PinkertonPetralogy. A treatise on rocks (Volume 1) → online text (page 32 of 35)
Font size
QR-code for this ebook

ranean, near Messina, and the noted Gulph of
Charybdis, sands which are moveable, when the
waves heap them on the shore; but which, by
means of a calcareous juice which the sea infil-
trates at that spot, harden gradually, so as to serve


for mill-stones. This fact is well known at
Messina ; and stones are incessantly taken from
the shore, without their being exhausted or the
spot being lowered. The waves throw fresh sand
into the vacancies ; and, in a few years, this sand
becomes so agglutinated, that the stones of new
formation cannot be distinguished from the an-


In 583, Saussure mentions rocks consisting of
alternate layers of limestone and calcareous sand-
stone, in the mountain of Buet. In the same
mountain there is a pudding-stone, composed of
fragments of grey and reddish quartz, reddish
felspar, and little yellow pyrites, united by a cal-
careous cement.

The molasse of Geneva is a sandstone with a
calcareous cement, and a mixture of clay ; it is
soft and impure. That of Lausanne is one of the
hardest and best : it is of a beautiful grey inclin-
ing to blue with a calcareous gluten. The moun-
tain of Voirons, two leagues from Geneva, chiefly
consists of calcareous sandstone*,

Calcareous sandstone, from Fontainebleau.

The same, from Livonia.

The same, from Gothland, Sweden.

* Sauss. 61, 1100, 273.


The same, from Swisserland.

The same, with limestone, from the south of
France, and various countries.

The same, in red and white layers, from Nor-

The same, of a brownish red with silvery mica,
from Metz. That city is chiefly built with this





Name, THE name Carbon is not the most happy,
as it arises from charcoal, an artificial sub-
stance, while carbon is now well known to
be an original element, which exists in the
purest state in the diamond, and enters
into the composition of siderite, perhaps


the most ancient of all the rocks. Char-
coal is now regarded as a mixture of car-
bon and hydrogen. By combustion it is carbonic acid,
converted into carbonic acid gas, formerly
called fixed air, or aerial acid ; whence
some writers have used the epithet aerated
lime, barytes, &c. for what are now called
carbonates of lime, barytes, and the like.
The discovery of this new air by Dr. Black,
led to wonderful improvements and a total
renovation of chemistry, which in its pre-
sent form has been called pneumatic, from
its spiritual foundations. It is indeed re-
markable, that the profoundest study, and
the most patient experiments, should con-
duct us from matter to spirit ; and thence
by a natural gradation of thought, to that
ineffable spirit, the Creator of the uni-

The carbonic acid gas, more briefly call-
ed carbonic acid, forms a constituent part
of the atmosphere, in the proportion of
about 1, in the 100, while the remainder
consists of about 77 of nitrogen and 22 of
oxygen gas. Combined with the earths, it


forms carbonates : and that widely extend-
ed substance called limestone, which is
often primeval, is a carbonate of lime.

Carbon itself not only appears in the
purest state in the diamond ; but forms
the preponderant part, sometimes even 90
in 100 of the substances now under view,
and which have therefore been called car-
bonaceous. They not only enter into the
composition of rocks, and some even of the
primitive, but form rocks themselves, as
coal has been found in masses of 80 or 90
feet in thickness. The trivial name of sea-
coal, arising from its importation at Lon-
don, might therefore well be exchanged for
that of rock-coal, as we say rock-salt.
Some might, perhaps, prefer the German
Bergarts. appellation of bergarts, implying sub-
stances of whatever kind which enter into
the composition of mountains ; or the
Greek geostromes, proposed by Patrin, to
denote the strata of the earth. But as the
conchitic beds of limestone, sometimes
more recent than coal itself, though often
in thin strata, universally assume the name


of rocks, any refined discrimination would
appear unnecessary. It has already been
more than once observed that the division
of mineralogy into three quite distinct and
separate provinces, METALLOGY, LITHO-
LOGT, and PETRALOGY, would be of the
utmost importance to the progress, illustra-
tion, and utility of the science ; each of
them being amply sufficient for the life and
labours of one man ; and, in this case, the
subjects under view could not be allotted
to any other grand division.



Characters. Texture, fine grained, but sometimes coarse,

Hardness, cretic. Fracture scaly foliated, some-
times slaty and uneven, sometimes rather con-
choidal. Fragments amorphous, rather sharp.

Weight, carbonose.

Lustre, metallic. Opake.

Colour, somewhat leaden, which occasioned
the vulgar, but very improper, name of black

When pure, it usually contains about 90 parts
oxyd of carbon, with 10 of iron ; but the foreign
kinds are often contaminated with large mixtures
of argil and silex, which renders them unfit for
the usual purposes of writing and drawing.
Sites. The best is that found at Borrodale, in Cum-

berland; a mine which has long supplied the
world with this valuable article; but the French
have lately succeeded in the fabric of an arti-
ficial kind. Graphite has also been recently
detected in the southern parts of Scotland, with
a singular kind of coal, called columnar, because
it appears like little basaltic prisms.



It is sometimes of a scaly appearance, which
Werner has arranged as a subdivision.

In the perusal of books of mineralogy, every
judicious reader must have remarked that, ac-
cording to the various dispositions of the authors,
they are fertile and satisfactory on some topics,
and barren on others : whence the great utility
of compilation, whose office, from the days of
Aristotle and the first dawn of science, has been
to collect, and arrange for the universal benefit,
facts and observations, which became more va-
luable from being concentrated. The prince of
the Roman poets compares this practice to that
of the bee, who prepares her elegant edifice and
useful honey from various flowers, some of which
only perfume the desert air. This work has,
therefore, without hesitation or apology, adopted
interesting descriptions from former writers,
whether domestic or foreign, but especially the
latter; for many excellent works are published
which will not bear complete translation, but of
which detached portions are highly satisfactory
and interesting. Such is the elementary treatise
on mineralogy by the ingenious Brongniart, di-
rector of the celebrated manufacture of porcelain,
at Sevres, whose accounts of graphite and an-
thracite (which will follow in its proper place),

VOL. i. 2 N


are the most ample and satisfactory which have
yet appeared.

Brongniart's " Graphite is of a grey almost black, with a
metallic lustre; it is soft, smooth, and even unc-
tuous to the feel ; its fracture granular ; it leaves
distinct marks on paper, clear, and of a bluish
black ; it even leaves marks on vitreous surfaces,
such as earthen- ware : its marks are grey, while
those of sulphuretic molybdena, which much re-
sembles it, are greenish.

" Its specific gravity is from 2,08 to 2,26. It
consumes and volatilises under the blow-pipe,
by a continued heat. Nitre renders its combus-
tion quicker and more sensible.

" Slightly rubbed on resin, it does not com-
municate any electricity to it, while it leaves a
kind of metallic coat.

" This substance, according to the experi-
ments of Mess. Berthollet and Monge, is com-
posed of iron and carbon, in the proportion of
0,90 of carbon and 0,09 of iron. The iron is in
too small a quantity to rank graphite among the
iron ores.

" I". Laminar Graphite. It is found in la-
mellas, or rhomboidal, or hexagonal spangles ; it
is of a tin- white.

" 2. Granular Graphite. It is in mishaped


masses, or compact lumps, with a granular frac-
ture, the grains more or less fine.

" Graphite seems to belong exclusively to pri-
mitive regions : sometimes it enters into the com-
position of the rocks which form those regions ;
sometimes it is found in masses, or in consider-
able layers. It is likewise met with in belts of
argillaceous schistus.

" It is found : in France, in the department
of Arriege, in large compact masses ; in the de-
partment of Mont Blanc ; in that of Sture, near
Vinay, above the baths ; in the mountain of
Lubacco, and in that of Gogni d'Orgial, in small
veins in granite. In the valley of Pellis, district
of Pignerol, department of the Po, in veins of a
yard in thickness, in granitic rock (Bonvoisin).
In Spain, near Sahun, district of Benabarra, in
the mountains ofArragon (Parraga), and near
Casalla and Ronda in the kingdom of Grenada.
In Bavaria : in Norway near Arindal ; this is the
laminar variety. In England, at Borrodale, two
miles from Keswick in Cumberland, this is the
most celebrated graphite mine; pencils of an
excellent quality are made of it, and recommend-
able, as being at once firm and soft. The bed of
graphite is in a rather high mountain, between
layers of a slaty schistus, crossed with veins of

2 N 2


quartz; the bed or vein which it contains, is
nearly three yards thick ; the graphite is there
found in large masses, but of different degrees of
quality; what is not good, is thrown away.

" Pencils, which are enclosed in cylinders of
wood, are made of graphite. In France they
are called mine de plomb, or capuchines. The
pieces of graphite are sawn in very thin quadran-
gular sticks, which are put in a groove made in
one of the halves of the wooden cylinder, which
is to form the envelope of this fragile pencil.

" The dust of the graphite, mixed with gum,
forms pencils of an inferior quality.

" This same dust serves to lay over iron, and
especially cast iron, to keep them from rust;
mixed with grease, it is used very efficaciously
to diminish the frictions in wheel engines.

" Also, mixed with argil, at Passau in Ger-
many, they make crucibles of it, which resist
extremely well sudden transitions of temperature,
and which are used by smelters.

" Laminar graphite is often formed artificially
in the flaws of cast iron, and in the cavities of
furnaces where iron is used. M. Fabroni af-
firms that it is also sometimes formed in the
humid way; and cites, on this occasion, the pits
dug in the territory of Naples : an acidulous


water is collected in them, at the bottom of
which, graphite is gathered every six months."*

Our ingenious author is mistaken, when he
says the graphite of Cumberland is found be-
tween layers of a kind of slate, traversed by veins
of quartz. Several specimens of the rock are
now before me.

1. Nodules of graphite in the rock itself: Graphite of


which appears decomposed, and in some parts
tinged with oxyd of iron, arising from the par-
tial decomposition of the graphite. The stone
easily yields to the knife, and is of a bluish grey
colour mottled with white. It has an unctuous
steatitic appearance, and seems to be a decayed

2. The same rock, at a further distance from
the mineral, and undecomposed. This seems a
Saussurite, or magnesian basaltin. It is of a
deep grey colour with dots of light brown, which
may be a decomposed felspar; and is mixed
with large patches, which approach the nature
of indurated steatite, of a light greenish grey,
mottled like the decomposed substance which
contains the nodules. It is, upon the whole, a
magnesian rock, of a particular description,
with a stong argillaceous smell, in this and other

* Brongn. ii. 53.


characters approaching to some serpentines ;
for that peculiar odour does not arise from the
argil, as commonly supposed, but from the iron
contained in the argil, and therefore expires from
many rocks not argillaceous. It is worth obser-
vation, that serpentine has never been observed
to <ontain any metal except iron, and its rela-
tives pyrites and garnet ; so that it is not sur-
prising that it should contain graphite, or car-
buret of iron. Perhaps the superiority of the
English kind may be owing to this circumstance,
the unctuous nature of the rock imparting that
quality to the mineral j as common flint becomes
menilite, from the unctuous and magnesian marl
in which it is deposited.

Another rock is found at Borrodale, I know
not if in contact with the former, but it appears
somewhat allied from the structure and nodules.
This seems to be a magnesian felsite, of a dark
grey colour, dotted with little reddish crystals,
and with greenish nodules. It is well known
that the British rocks are often anomalous, or
transilient, and can scarcely be reduced to pre-
cise denominations, till the science shall have
made a far greater progress than it has at

of chamouni. Saussure discovered graphite, which, with the
writers of that time, he calls plombagine> on


schistose quartz, among the Alpine fragments in
the valley of Chamouni ; but upon reaching the
rocks, it only formed a kind of gneiss, being thin
plates of graphite interposed between layers of
quartz, thus assuming as it were the place of
foliated mica.


Aspect 1. Fine. From Borrodale, near Kes-
wick, in Cumberland.

The same, in nodules in the rock already de-

The same, as found with columnar coal, from

The same, from the north of Italy, France, &c.

Aspect 2. Coarse. This is commonly mixed
with silex, argil, and other impurities.

From various parts of France and Germany.


With laminar quartz, from the valley of Cha-

From Arindal, in Norway.

Laminar graphite, interposed at certain inter-
vals in gneiss, from Greipon, in the Alps. Com-
municated by Gillet Laumont.



Characters. Texture, schistose and incoherent.

Hardness, cretic. Fracture, slaty. Frag*
ments, amorphous, rather sharp.

Weight, carbonose.

Lustre, sometimes dull, but generally glisten^
ing and even metallic. Opake.

The colour is often a dark black, but some-
times has a metallic reflection, which is particu-
larly conspicuous in that elegant kind called
Kilkenny coal ; and which might with much
Kirwanite. propriety be called Kirwanite, in honour of the
great Irish mineralogist, who first introduced it
to scientific attention. The French continue,
most unaccountably, to confound it with canel
coal, which is quite a different substance*.

Anthracite seems to have been first observed
by Dolomieu; but Born, in his elegant cata-
logue of Miss Raab's collection of minerals, has
classed it under graphite, which he calls plom-
bagine, or carburet of iron, in the following

* In order to obviate this error, the author, among many other
British substances, placed specimens of Kilkenny coal in the
museum of the Jardin des Plantes, and another great collection at



terms. It must not at the same time be for-
gotten, that Pliny uses the word anthracites, in
a very different sense, for a gem which has the
effulgence of burning coal.

" Coaly Plombagine. Anthracolite.

" This kind of plombagine has recently been Bom's


discovered at Schemniz, in Hungary, which dif-
fers from the known plombagine, as being very
light, compact, brittle, of a shining and con-
choidal fracture, and without soiling the fingers
is easily broken. It has but very little iron in
its mixture, and therefore when calcined under
a muffle, slowly dissipates, and loses 90 parts of
its weight. According to the analysis, lately
made at Schemniz, in Hungary, in 100 parts
there are 90 of carbon, 5 of argil, 3 of iron, and
2 of silex.

cc It seems to have some affinity with the in-
combustible pit-coal, described by M. de Mor-
veau in the new Memoirs of the Academy of
Dijon. Prem. Semest. 1783, page 7686.

" Mr. Struve has just given the description
and analysis of a fossil, which, with the excep-
tion of the colour, still more agrees with this
variety of plombagine. He calls it also coaly
plombagine. See Journal de Physique, 1790,
January, p. 55.

" Black compact coaly plombagine, with



a shining fracture ; of Pacherstolln atSchemniz,
in Hungary.

" It adheres to a blue argil, greyish, mixed
with pyrites. The vein, in which it is found, is
filled with this argil, which is only a decomposi-
tion of the metalliferous rock. It is in this argil
that different sized pieces of this coaly plomba-
gine are found, which for the most part have a
cylindrical form. They even seem to be com*
posed of concentric layers round a kernel ; in
short, this plombagine nearly resembles wood,
and to all appearance has a vegetable origin."

Estner also agrees in the wood-like appear-
oftheAips. ance of this anthracite. Among other rocks
presented to me by Gillet Laumont, are different
specimens of anthracite, which he says is also
called houille slche> or dry coal. There is parti-
cularly a specimen of that mentioned by Dolo-
mieu, as belonging to primitive -regions, and
containing no traces of vegetables, from little
St. Bernard, in going to the fort in the Alps.
This is accompanied by the following specimen
and note : " Vegetable impressions, which I first
discovered in 1803, serving as a roof to the same
anthracite, or dry coal, the wall or under-rock
being also a schistus. I had one very fine, with
little ramified plants, and another with reeds.
A little impression is on this specimen 5 but -the


finest are in the cabinet of the Council of Mines."
Another specimen of anthracite is from Allues,
Mont Blanc ; and a third, which is slaty, is from
Regny, near St. Simphorien de Laie, on the road
from Roanne to Lyons.

The best account of anthracite, as already
mentioned, is that given by Brongniart, which
shall therefore be translated.

" Anthracite so much resembles coal, at first


sight, that for a long time it was taken for a
variety of that combustible mineral. Neverthe-
less, artisans who used it had remarked, that it
burnt with great difficulty, and did not produce
either that white flame, or black smoke, or
that bituminous odour which arises from coal ;
therefore it was called, incombustible pit-coal.

" Anthracite is of a black less opake than
coal ; its colour approaches nearer by its bright-
ness, to the metallic black ; it is also more fri-
able ; it is rough to the touch, and easily stains
the fingers,; it leaves a black mark on paper,
which, if examined with attention, seems of a
dull black. These characters serve to distin-
guish it from graphite, which leaves a bright
mark, and is unctuous to the feel.

" The texture of anthracite, sometimes schis-
tose, sometimes compact, at others granular, is
too various to serve as a characteristic. Its spe-


cific gravity, which is 1,8, is inferior to that of
graphite, in the proportion of 9 to 14; and ex-
ceeds that of coal, as 9 to 7.

" This mineral is decidedly opake, it easily
allows the electric spark to pass, is hard to burn,
and in its combustion never produces but one
substance, which is carbonic acid.

c( The matter essential to its composition, is
mixed carbon ; or perhaps combined sometimes
with silex and iron, sometimes with argil and
silex, in very different proportions, according to
analysed specimens.

" 1. Friable Anthracite. It is in mass, gra-
nular, not schistose, greatly soiling the fingers,
and easily crumbles.

" 2. Scaly Anthracite. It divides into large
solid scales, the surface of which is unequal, un-
dulated, and shining; it soils the fingers less
than the preceding.

cc These two varieties are found at the villages
of Arrache and Macot, in the neighbourhood of
Pesey, department of Mont Blanc.

" 3. Schistose Anthracite. (Hany.) It di-
vides into lamince, with an uneven and undulat-
ing surface.

" 4. Globular Anthracite. (Hauy.) It is
found in small globular masses, in crystallised
carbonate of lime, at Kongsberg in Norway.


" Anthracite is often found in primitive re-
gions, which is a remarkable circumstance in a
combustible which seems so nearly allied to coal.
It generally is found in mica-slate, and even
gneiss; it is sometimes in beds, sometimes in
veins. Its layers are often winding and con-
torted, like those of the rocks with which it

" Dolomieu saw anthracite in veins, in the
porphyritic mountains near Chapelle, department
of Saone and Loire. In the Tarentaise of Savoy,
it contains 0,72 of carbon, 0,13 of silex, 0,03
of argil, 0,03 of iron, and 0,08 of water. Primi-
tive anthracite is found in Piedmont, at the foot
of little St. Bernard. In the department of
Isere, in lumps or heaps, in the midst of a pud-
ding-stone, composed of primitive rock, and
without any vestige of organised bodies. At
Musy, near Clayte, in the former Charolais.
At St. Simphorien de Laie, in the environs of
Roanne. At Diablerets, in Valais.

" M. Ramond has mentioned an interesting
variety, which he found at the bottom of the
valley of Heas, the upland of Troumose, depart-
ment of Upper Pyrenees, in the midst of mica-
slate. This anthracite disposed in veins, only
contains carbon, mixed with a small quantity of
silex and argil, there not being any iron. This



circumstance fully distinguishes anthracite from

" M. Fleuriau de Bellevue has found anthra-
cite crystallised in regular hexaedral plates, on
a granitoid, which is found in isolated blocks on
the quays of Saardam, in Holland*. It is
thought these rocks have been brought from
Norway. This anthracite, according to M.
Vauquelin, only contains carbon, silex, and

" Anthracite is also mentioned in the neigh-
bourhood of Schemnitz, in Hungary, in a vein.
At Kongsberg, in Norway, it is mingled with
native silver. In Spain, in the port of Pajares;
which separates the kingdom of Leon from the
principality of the Asturias, it reposes on a clay-
slate; and, according to M. Proust, contains
0,93 of carbon, and 0,07 of sand, argil, and iron.
It is used in painting, the same as lamp-black.
(D. B. Canga-Arguelles.)

" Anthracite is not exclusively found in pri-
mitive regions. M. Hericart-Thury has shown
that that which is found in the department of

* In the curious collection of rocks formed by the venerable
Besson, formerly director-general of the mines of France, the author
was surprised to find numerous specimens from Zealand ; and the
possessor has even adduced them as such in his printed works,
They were from ballast thrown on the quays of Zealand. The
quays of London furnish many curious rocks.



Isere, near Allemont, towards the summit of the
mountain of Challanches, at an elevation of 2563
yards, is secondary. It lies between two beds
of black schistus, covered with impressions of
vegetables; it contains no bituminous matter,
and has 0,97 of carbon, so that it is nearly pure
carbon. That of Rousses, opposite the same
mountain, and that of Venose, near the village
of Oysans in the same valley, are also of se-
condary formation. The anthracite of Lisch-
witz, near Gera in Saxony, is in layers of
clay-slate, covered with vegetable impressions.

" The anthracite which contains no indication
of vegetable coal, is wholly incombustible ; that
which contains any, may burn, if two-thirds of
charcoal be added to it. (Hericart-Thury.)"*

Brochant observes, that if anthracite be held
a long time on fire, moving it often, it consumes
slowly without any flame; but only encircled
with a little glory, or irradiation, like red iron
and diamond. During this operation it loses
about two-thirds of its weight, and the residue is
of a blackish grey, which announces that the
combustion is imperfect.

* Brongn. ii. 55.


It is worthy of remark, that as anthracite
has been found in a primitive glutenite or pud-
ding-stone, so the usual gangart of diamonds,
both in Hindostan and Brazil, is a ferruginous

Online LibraryJohn PinkertonPetralogy. A treatise on rocks (Volume 1) → online text (page 32 of 35)