John Pinkerton.

Petralogy. A treatise on rocks (Volume 1) online

. (page 22 of 35)
Online LibraryJohn PinkertonPetralogy. A treatise on rocks (Volume 1) → online text (page 22 of 35)
Font size
QR-code for this ebook


slate.

" The mountain called Roth Horn, or Red * th Horn -
Horn^ and which faces Mount Rosa, towards
Italy, is elevated 1506 fathoms: it is composed
of compact serpentine, divided into irregular
masses of an immense size. The surface of this
serpentine becomes red by the action of the
atmosphere, which oxyginates the iron it con-
tains to the highest degree. It is this colour,
and the elongated form of this mountain, which
have procured it the name of the Red Horn.

" This serpentine is covered by a steatite, of
a sea-green colour, mixed with carbonate of
lime, and grains of felspar. On this steatite
beds of calcareous micaceous schistus repose, in
which the mica contained is more than one half.
These schisti are again covered by serpentine :
all the beds are nearly horizontal, a little raised



342 DOMAIN IV. TALCOUS.

towards Mount Rosa. Geologists will perceive
the importance of this observation.

" Mount Cervin, another mountain near
Alount Rosa, is an inaccessible obelisk, of a tri-
angular form, which is elevated to the prodigious
height of 2309 fathoms above the sea, according
to the trigonometrical measurement, taken witb
the greatest exactness, by Saussure. It is com-
posed of three distinct masses, piled the one on
the other.

" That which forms the summit is of a yellow
Isabella colour. It is composed of serpentine,
mixed with micaceous schistus, calcareous, and
quartzy. Saussure has thus judged of its con-
struction from other neighbouring summits,
which he has visited, and which present exactly
the same colour.

" The mass which is under this is of a grey
colour, and formed of gneiss and quartzy mica-
ceous schistus. Saussure saw some of its frag-
ments.

<c The third exactly resembles the first; and
Saussure found that it is also of serpentine, al-
ternating with calcareous micaceous schistus.

" The base of the pyramid is of serpentine,
but of a confused structure.

" I repeat, that mountains of serpentine are
seldom of a great elevation ; and that those



MODE VI. SERPENTINE. 343

about Mount Rosa are owing to a peculiar and
local circumstance.

" One of the most remarkable hills of serpen- Magnetic

L hill.

tine, on account of the phenomena which it pre-
sents, is that observed by Humboldt, in 1793, in
the chain of mountains which separates the mar-
graviate of Bareith from the Upper Palatinate.

" This hill is only elevated fifty fathoms above
the neighbouring plains : it extends in length
from east to west, its skirts consequently are to
the north and south.

" The rocks which crown its summit are of a
very pure serpentine, which, by its colour and
foliated fracture, approaches schistose chlorite.
It is divided into tolerably distinct beds, and re-
poses on a veined granite, mixed with horn-
blende.

" Humboldt having brought his compass near
these rocks of serpentine, saw with surprise, that
the north pole flew round quickly to the south.
He farther observed, that the rocks of the north
declivity, and those of the southern, have their
poles directly contrary. In the former are only
found south poles, and in the latter north poles.
The eastern and western extremities of the hill
are in a state of indifference, and do not mani-
fest any action on the magnetic needle, though
otherwise the rock affords the same appearance.



344 DOMAIN IV. TALCOUS.

" In the magnetic parts of this hill certain
rocks are also observed, which have no action,
by the side of similar rocks, which have a very
strong one. Some affect the needle at the dis-
tance of 22 feet.

cc This mountain^iot only exerts its action on
the magnetic needle in its whole mass, like some
other mountains, but it is manifest in even very
small pieces. Humboldt has observed, that frag-
ments, scarcely visible, are briskly moved, upon
presenting to them, one after the other, the poles
of the weakest magnet: and it is remarkable,
that a substance possessing such a decided po-
larity, has not the least attraction on iron not
magnetised.

" Humboldt convinced himself that this ser-
p'entine does not contain an atom of magnetic
iron ; all which it contains, and which colours
it, is in the state of oxyd. It is for naturalists
to explain the cause of so remarkable a pheno-
menon.

" The specific gravity of this serpentine is
much less than that of others; it only extends
from 1900 to 2000, while the ordinary weight
of this rock is 2700, and even reaches, as Saus-
sure has observed, to 3000, in certain varieties
which he found in the vicinity of the lake of
Geneva.



MODE VI. SERPENTINE. 345

<c M. Chenevix, the chemist, who has em-
ployed himself in a succession of analyses of
magnesian rocks, found that serpentine and ol-
lite are composed of the same elements; and
that, according to a medial sum of many ana-
lyses, they contain, silex 28, argil 23, magnesia
34, oxyd of iron 4, water 11."*

The name serpentine seems to have been de- Name,
rived from the Italians, who however applied it
in differently to several substances; as black
porphyry was called serpentino nero, and the
green porphyry serpentino antico\. The name,
which was vague at first, was afterwards con-
fined to this magnesian rock, to which it is most
strictly applicable, from the variegation and
unctuous appearance of the colours.

Ferber has minutely described several of the
Italian serpentines, particularly that of Impru-
neta, near Florence. The colours are white,
red, black, yellow, and green ; sometimes uni-
form, sometimes intermingled. It is often inter-
sected by small veins of asbestos, and sprinkled
with an unctuous micarel, of a greenish silvery

* PatrinMin. i. 177.

t Wall. i. 432. It is singular that this truly learned author
should have followed the common error concerning the ophites of
Pliny.



346



DOMAIN IV. TALCOUS.



Useful in
the arts.



Nephritic
stone.



hue, of a square form, and not hexagonal, like
mica. There are also perpendicular veins, from
six to twelve inches in breadth, containing the
following substances: 1. Farinaceous steatite,
or soap earth, white and green. 2. Chalk of
Briancon. 3. Fibrous steatite, passing to as-
bestos. 4. Asbestos. 5. White and green ami-
anthus. As he wrote in 1772, in the mere dawn
of genuine mineralogy, his names are modified
by his descriptions.

As serpentine, like ollite, resists fire, it would
be found of far more utility in domestic and pub-
lic monuments than marble; yet its use has
been unaccountably neglected, both in ancient
and modern times. The beautiful serpentines
of Portsoy, the singular white- veined marbles of
Durness, and the most elegant of all the marbles,
that of Tirey, with the fine green serpentine
marble of Anglesea, might supply the British
empire with decorations far exceeding the fa-
shionable imports from Italy, the insipid marbles
of Carrara and Sienna, especially at a period
when we should only enrich our enemies.

Serpentine, like the other magnesian rocks,
impressed the ancients not irrationally with an
idea of medical qualities. Internally they would
act as absorbents; but the nephritic stone was



MODE VI. SERPENTINE. 347

supposed, when only worn, to cure diseases of
the reins, or the lumbago*. This nephritic
stone is often found in flat pebbles on the shores
of the sacred island Hyona, among the Hebudes
of Scotland. It approaches to what is called
jad, the giada of the Italians, and is also found Jad.
in the island itself, adjacent to fine white mar-
ble. As jad however has never been yet ob-
served to constitute a rock, but, according to
the imperfect observations, has only been found
in rivers in schistose fragments, whence it would
seem only to form thin layers, it has not been
admitted into the present work. It must also
be observed, that the analyses hitherto given of
this substance are not satisfactory. The jad,
which forms the base of the composite rock
called the Corsican green, has been pronounced
by Werner to be a felsite, or compact felspar;
and if the analysis of the younger Saussure be
trusted, it contains no magnesia. It may seem
to be nearly the same substance with the iconite
of the Chinese, only in a far higher state of in^
duration. This substance has also, by some
writers,, been called lemanite, from the Lacus
Lemanus, or Leman Lake, now called the Lake

* According to others, the stone, or gravel 5 in which sense it is
used by modern physicians. See Johnson.



348 DOMAIN IV. TALCOUS.

of Geneva, upon whose shores it was found by
Saussure.

Werner and his disciples have continued the
ancient name of nephrite to jad, which they
class among the magnesian rocks ; and they di-
vide it into two sub-species; the oriental, which
is brought from China and the East*, and what
they call beilslein, or axe-stone, because it is
brought in the form of axes from South Ame-
rica, whence it might strictly be called occi-
dental. It is to be regretted that no able che-
mist, no Klaproth nor Vauquelin, has analysed
the various kinds of jad, though a stone of cele-
brated beauty and utility ; and it remains un-
certain, whether it ought to be referred to the
magnesian, the argillaceous, or whether it may
not even be an unctuous keralite, resembling
unctuous quartz. It may perhaps even be of
various kinds and compositions, afterwards to
be distinguished by new appellations. Recent
French writers have called it felspath compact
jadien-\, which, they add, is the jad of the lapi-

* Wad, p. 23, mentions different monuments of nephrite, among
which one of a leek green, which, he adds, is giada, and is marked
with Persepolitan characters. Roziere brought from Egypt a frag-
ment of red granite, marked with the same letters, from a monu-
ment which, if I remember right, he discovered in the Desert of Suez.

f Brard, 166.



MODE VI. SERPENTINE. 349

daries, and the nephrite of the Germans ; only
different from other compact felspar by its tena-
city, weight, and unctuous appearance, while it
melts under the blow-pipe like other felspars.
The able and ingenious Haiiy has added the
lemanite, or white jad, as an appendix to fel-
spar, under the name of felspath tcnace ; while
he ranks jad, the nephrite of Werner, among the
substances whose characters are not sufficiently
known to find a place in the system. He re-
gards the axe-stone as totally different from the
oriental jad, of which he gives two analyses, one
by the younger Saussure, who found iron, man-
ganese, soda, pot-ash, &c. c. and has acquired
little reputation as a chemist. Karsten, in his
tables of mineralogy, Berlin 1808, has given
another, by Kastner, which is probably authen-
tic, and deserves repetition ; silex 50, magnesia
31, argil 10, water 3, oxyd of iron 5, with a tint
of chrome.

Mineralogists having in general supposed that
jad or nephrite occurs in veins or layers in ser-
pentine rocks, it was proper some account should
be given of so remarkable a substance. For the
same reason, it may be proper here to mention
asbestos and amianthus, almost constant in the Asbestos.

. i D . 1-1 11 Amianthus.

midst ot serpentine, but which cannot be regarded
as forming rocks. The 1 ate ingenious Dr. Walker,






350 DOMAIN IV. TALCOUS.

professor of mineralogy in the University of
Edinburgh, who repeatedly visited the Western
Isles of Scotland, is said to have asserted, that
the little isle of Bernera, which terminates the
exterior chain of the Hebudes, is composed of
amianthus, or, as he more probably intended, a
mixture of asbestos and amianthus. Lord Sea-
forth, the excellent proprietor of these remote
regions, and himself a mineralogist, when con-
sulted by the author, answered, that so singular
a circumstance was unknown to him, though it
could scarcely have escaped his information.
The finest amianthus occurs in Corsica, forming
beautiful white silky threads, of two feet or more
in length ; and it is so abundant, that Dolomieu
used it instead of flax to pack his minerals.
There is also a mountain in the Uralian chain
which is called the Silky Mountain, as in the fis-
sures of a Saussurite or magnesian basaltin there
is found an amianthus, which at first appears
compact and hard, but when exposed to the air
for some months, it swells, and becomes a fine
down, as flexible as cotton*. But even this can
scarcely be said to form a constituent part of
the mountain, and amianthus on a smaller scale
is frequent in rocks of this description ; so that

* Patrin, i. 2l6.



MODE VI. SERPENTINE. 351

it must continue to be regarded as a parasitic
substance : and if even a rock or hill consisting
solely of asbestos and amianthus were discover-
ed, it must be classed among the anomalous, as
being contrary to the usual course of nature.

Having thus discussed the chief parasitic sub-
stances which are found in serpentine, it is pro-
per to return to the immediate consideration of
that celebrated rock.

Werner and his disciples divide it into two of
their barbarous sub-species, under the epithets
Common and Noble; the latter being trans- sei ^entine,
parent, and chiefly found in Silesia. It is gene-
rally of a dark leek green, and of an unctuous
visage. Mr. Jameson says that in Italy it is
called nephrite, with which it might perhaps be
classed. But when Brochant supposes that the
verde antico, and other green marbles well known
in Italy, belong to the noble serpentine, he for-
gets that they are all opake, while the latter is
translucent. When he quotes Estner, who con-
founds the verde antico and ophite with green
porphyry, the confusion is infinite; for the verde
antico is a marble, which will presently be de-
scribed ; and the ophites, as already shown, is a
mere error, echoed by mineralogists for a cen-
tury and a half, while the ophites of Pliny is an
ollite. The noble serpentine of Werner, which



352 DOMAIN IV, TALCOUS.

is found in small masses or disseminated, seems
rather to belong to lithology or gemmology.



STRUCTURE I. ENTIRE.

Black serpentine, from Egypt.

Brownish serpentine, from the same. These
are small statues, described by Wad.

Serpentine, with white spots, from Cecilia, near
Volterra, Tuscany.

Black, from Monte Ferrato-di-Prato, call Nero-
di-Prato.

Green, from the same, Verde-di-Prato.

Gabbro, or serpentine of various colours, from
Impruneta, seven miles south from Florence.

Green serpentine, with yellow spots, from the
Sierra Nevada, in Spain.

Serpentine, shaded with various tints of green,
from the Pyrenees*.

Deep green magnetic serpentine, from Bareuth.

Green serpentine, marbled with white, from the
Vale of Chamouni.

Serpentines, from Corsica and Italy.

* The erroneous ophite of Palassou, whose work on the Pyre-
nees has great merit. See his prolix dissertation on this pretended
ophite, Journ. des Mines, v. 31. He is however nearer the truth
than Gesner, and his successors, who supposed ophite to be green
porphyry.



MODE VI. SERPENTINE. 353

Brown serpentine, spotted with red, from the
Lizard point.

Dark green serpentine, from the same : perhaps
the name of the cape is derived from the colour.

Serpentine, of various colours, from Portsoy.

Yellowish serpentine, from Zoblitz, in Saxony.

Black serpentine, spotted with red, from the
same.

Green serpentine, in pebbles, from the Lake of
Geneva.

Granular serpentine, from the Alps.

Serpentine, from the mountain of Cervin.

STRUCTURE II. MINGLED.

With mica, from the Lizard point, &c.

With veins of steatite, from Cornwall, Portsoy.

With asbestos, from the same.

With amianthus, from Zoblitz.

With foliated steatite, amianthus, and garnets,
from the same.

With garnets, from Bohemia.

With asbestos and calcareous spar, from Prato.

With spangles of satiny diallage, the smaragdite
of Saussure, from Impruneta.

With metallic diallage, from Saxony.

With the same and epidote, from Queyras, near
Briancon.

VOL. r. 2 A



354? DOMAIN IV. TALCOU9.

Saussure presents some uncommon examples :

Serpentine, with spots approaching to crystal-
lisation : may not this be the stone mentioned by
Pliny as gemmose ? 107-

Laminar serpentine, of a yellowish grey, with
striated surfaces, and translucent on the edges.
2253.

He also describes, 1434, another granular ser-
pentine, with an earthy fracture.

Mount Cervin rises to a prodigious height, un-
der the form of a triangular obelisk of bare rock,
which seems hewn with a chisel : the appearance
is alike singular and magnificent. Saussure,
2220, gives a curious account of this surprising
mountain of serpentine.



MODE VII. SAUSSURITE.

Characters. Texture, fine-grained, compact.

Hardness, basaltic. Fracture, generally even
and earthy, sometimes scaly. Fragments, amor-
phous, rather blunt.

Weight, granitose.

Lustre, dull, sometimes rather glimmering,
from particles of siderite. Opake.

Colour, black or dark grey, sometimes faintly



MODE VII. SAUSSURITIJ. 3J5

verging towards the green, from an excess of
magnesia.

This stone may be regarded as intermediate
between basaltin and serpentine, and might be
called magnesian basaltin ; but as it is the most
remarkable pierre de corne of Saussure, it has
been thought proper to give the name of that
great observer to this important rock.

The pierre de corne, or corneenne, is a vague
appellation, still retained by the French mine-
ralogists. It sometimes implies a trap, some-
times a wacken, sometimes an earthy siderite ;
and sometimes more appropriately the present
rock. Saussure has observed, 1225, that when
the cornienne appears crystallised, it assumes
the name of hornblende. He has given, 725,
an analysis of his pierre de corne, and observes,
that the chief difference between it and basalt
is the mixture of magnesia. In Kennedy's ac-
curate analysis of basalt there is no trace of
magnesia ; but in the Saussurite there ought to
be more than 6 in the 100. The decomposition
of the iron often forms a kind of bark around
this stone, whence it has been called by some
authors pierre-a-ecorce.

Dolomieu, in his celebrated memoir on felsite
and trap, which precedes his distribution of vol-
canic products, observes, that the cavities in

2 A 2






356 DOMAIN IV. TALCOUS.

trap are commonly filled with calcareous spar;
while those of his roche-de-corne, or Saussurite,
besides calcareous spar, often present a green
With steatite, steatite extremely ferruginous *. This feature,
with the occurrence of amianthus, and other
modes of talc, confirms the magnesian propen-
sity of this rock ; and as these green nodules
are also frequent in amygdalite, it is to be sus-
pected that the latter, to the base of which va-
rious denominations have been assigned, may,
when duly analysed, be found to belong to this
division.

Dolomieu also considers the chlorite slate of
Werner, which often presents octahedral crystals
of iron, as intermediate, between the roche de
corne and the talcs ; while the former graduates
from trap to serpentine.

cc In Tuscany there are frequent examples of
these passages of rochc de corne to serpentine.
At Pietra Mala, on the ridge of the Apennines,
to the right of the road from Bologna to Flo-
rence, there is a mountain which presents all
the kinds of gradations between serpentine and
roche de corne, and the passage of the earthy
grain of this to the scaly texture of hornblende,
or corneus spathosus. This roche de cornc, of a

* Journal de Physique, 17Q4, p, 258.






MODE VII. SAUSSURITE.

black base, marked with white and green spots,
has been taken for a lava by many naturalists,
among others by Mr. Ferber."*

That the corneenne is a term which ought to
be dismissed from mineralogy, will sufficiently
appear from the following description, by Brong-
niart, a very industrious and exact mineralogist*

" Corneenne f is a rock very difficult to deter-
mine, and still more difficult to confine to pre-
cise limits. On one side it approaches very
near to wacken, and on the other to argillaceous
schistus : it has besides numerous relations with
basalt, and even with amphibole, or hornblende.

" This rock is generally compact and solid ;
its fracture is dull, rather even, but irregular; it
yields by breathing on it a very sensible argil-
laceous odour ; it is generally difficult to break,
causing the hammer to rebound, and presenting
a kind of tenacity, which throws it at a distance
from wacken, and approaches basalt. It often

* Journal de Physique, 1794, p. 258.

" -f* Corneus. Wall. This genus contains the greater part of our
amphibole hornblendes. Corneenne rock, Hatiyj omitting the va-
rieties 2,3, and 4 vulgarly pierre de corne.

f< This species must not be confounded with the hornstein of the
German mineralogists : it has been seen that this was a silex.
Corneenne must also be distinguished from the roche de corne of
Saussure, which seems to be a trap rock, in the acceptation that we
give to that word, according to Mr. Werner."



DOMAIN IV. TALCOUS.

possesses sufficient tenacity not to be scratched
by the copper knife, which, on the contrary,
leaves its mark. It is even difficult sometimes
to be scratched with iron.

fe Corneenne is easily melted into a black
bright amel, and this character distinguishes it
from schistus, when it possesses the texture of it,
and from schistose jasper, when it approaches it
by its hardness : it almost always acts upon the
magnetic needle.

" Most mineralogists look upon this rock as
an intimate and invisible mixture of amphibole*
and clay.

" We shall establish the following varieties in
this species :

cc 1. Compact Corneenne. It is solid, com-
pact, difficult to break ; its fracture is uneven,
passing to the conchoidal.

" I will give, as an example of this variety,
the brown paste, approaching to the violet, of
the amygdaloids of Drac. Dolomieu considered
it as a corneenne well characterised. The paste
of the amygdaloids of Derbyshire, called toad-
stone, should be equally placed with it, and that
of the agates of Oberstein, &c.

* An absurd name for hornblende or siderite, signifying forsooth
ambiguous, while there is no substance less ambiguous. P.



MODE VII. SAUSSURITE. 359

" 2. Trap Cornienne*. This variety is hard 5
it wears iron, but does not sparkle ; it is com-
pact; its grain is consequently fine, close, and
absolutely dull. This is what distinguishes trap
from basalt; the latter always showing in its
fracture a grain rather crystalline. It breaks in
parallelepipeds : its fracture is sometimes con-
choidal. Its most general colour is black, but
there is some, bluish, greenish, and reddish.
(Wall.)

" The trap here mentioned is an homogenous
rock. It is easily distinguished by its charac-
ters from the trapose rocks.

t( This rock is very common in several parts
of Sweden.

" 3. Lydian Corncenne^. This cornienne is
black, dull, compact; it is softer than the trap,
or corneenne, and has not the parallelopided frac*
ture : it is, on the contrary, perfectly compact,
and sometimes rather schistose : it is scratched
not only by iron, but also by copper, when the
angle or edge of a piece of copper is applied;
but when this rock is rubbed with the flat or



** * Corneus trapezius. Wall. Trap is a Swedish word, whictj.
means stairs. This name has been given to this corneenne, because
the mountains which it forms present a kind of steps or seats iu
their declivities." (Wall.)

** f Corneus trapezius. Lapis Lydius" (Wall.)



360 DOMAIN IV. TALCOUS.

rounded part of a copper instrument, it receives
the mark of the metal. It is by these characters
that it is distinguished from the blackest and
most compact argillaceous schisti; they being
always scratched by copper, and never receiving
any mark from it, however applied; besides,
schisti do not melt like cornfenne.

" It is on the property, which the Lydian
cornienne possesses, of receiving the mark of cer-
tain metals, that the use that is made of this
stone, to judge by sight of the quality of gold,
is founded. It is vulgarly called touch-stone*.
It has also the name of Lydian, because the
ancients gave that name to touch-stone ; but it
no longer comes from Lydia. Those at present
used come from Bohemia, Sa&ony, and Silesia.
I dare not however affirm that the touch-stones
of those countries are all related to this variety
of cornienne. It is even probable that, the
greater part among them are basalts.

<c The Lydian corntenne, of which we are here
treating, is that used as a touch-stone among

" * Touch-stones, and the manner of using them, will be spoken
of more in detail in treating of the uses of gold. It is probable that



Online LibraryJohn PinkertonPetralogy. A treatise on rocks (Volume 1) → online text (page 22 of 35)