400 Earths. MINERALOGY. Earths. 
kins's colledion, different in ffyle, but equal in merit, to 
the early gems of the Egyptians. - 
“ Ancient Hindoo gems, however,” replies Mr. Land- 
feer, “are very fcarce in comparifon with the gems of 
Egypt, or even with thole efteemed Perfepolitan ; and, 
when the imperifhable nature of their fubltances is con¬ 
sidered, their fcarcity is certainly no corroboration of Mr. 
Rafpe’s hypotliefis. Indeed, much as the tenor of this 
gentleman’s treatife is to be admired, I cannot think his 
reafoning in this place will fafeiy carry us farther than 
to Ihow the Hindoo extradion of the lapidary’s procefs, 
which in all probability was invented before the engraver 
had learned to exercife his art on the precious materials 
produced from, the mines of Hindooftan. But perhaps 
even the lapidary’s procefs was not at that time per¬ 
formed by means of diamond-powder. It appears to me 
more probable that the corundum-ftone (commonly term¬ 
ed adamantine fpar) was ufed both by the Hindoo lapi¬ 
daries and the engravers of Egypt. This fpar has not 
been known in England above thirty-five years, and was 
very imperfectly known until about fix years ago, when 
its hiftory and properties were communicated to the Royal 
Society by the hon. Mr. Greville, on unqueffionable au¬ 
thorities tranfmitted from India. It is at p re lent em¬ 
ployed in the cutting and polifliing of precious Hones, by 
the Indian lapidaries, and alfo by thofe of China ; and has 
been fo employed from time immemorial. It is, of all 
fubltances, in point of hardnefs, next to the diamond, and 
confequently will operate on all llones that are lefs hard ; 
and, as it is found in great quantities in the peninfula of 
India, where the natives ufe it as we do emery, it is very 
likely to have be*en carried along with the precious Hones 
to Egypt; or it is even probable that Egypt itfelf pro¬ 
duces the corundum-ffone. From Mr. Greville’s memoir, 
combined With what is mentioned in the Encyclopaedia 
"Britannica under the article Emerald, I am inclined to 
think, that, if the famous emerald-mine in the Thebaic 
defert fltould be re-difcovered, its product would be found 
to be no other than the green corundum-Hone. Pliny 
informs us that the Romans ufed to import land for the 
purpofes of cutting and polifliing hard Hones, from Ethi¬ 
opia and from India, which Hind was probably no other 
than the grit or powder of corundum. Had the Egyp¬ 
tians poffeffed any better means of effecting this purpofe, 
it would probably have been tranfmitted through the 
Greeks; and Pliny would have known and mentioned it.” 
Lectures on Engraving, 1807. Phil. Tranf. 1798. 
.Order VII. AGGREGATE or MIXED EARTHS. 
Granites, Granite.—ConiiHing of parts, mofily in the 
form of cryftals, cohering without any intermediate ce¬ 
ment, and mixed without any determinate order; gene¬ 
rally of a granular texture, hard and durable, and admit¬ 
ting a fine polilh : conffituting the principal material and 
nucleus of primitive lofty mountains. 
The effential ingredients of granite are feldfpar, 
quartz, and mica, being the fame as thofe of (the next 
genus) gneifs, from which granite differs chiefly in the 
arrangement of the three component parts : their being 
mingled without order or regularity, produces a granular 
ftrudure, while that of gneifs is generally fluty. It is, 
probably, this granular nature of the rock in queffion 
which has procured it its name; though Home authors are 
of opinion that the word granite is nothing but a corrup¬ 
tion of geranites, a name mentioned by Pliny, as that of 
a Hone of the colour of a ffork’s neck. The fad is, that 
the word granite, which is now' adopted by almoff all 
European nations, originated with Italian antiquaries $ 
and Tournefort was not the firff writer who makes men¬ 
tion of it. 
Belides the three conffituent parts of granite, the addi¬ 
tion of hornblende, tourmaline, or garnet, is not under- 
Hood to alter the genus of the Hone, but only to conftitute 
a fpecitic difference. The proportions of thele conitituent 
parts vary exceedingly; but the felipar is upon the whole 
inoff abundant, and from this in general is derived the 
predominating colour of granite, pf which there are fixty- 
tw'o fpecies. According to Sauffure, the proportion of 
felfpar in Mont Blanc and the neighbouring rocks, is 
nearly three-fourths : the fame rocks contain fcarcely any 
mica; the place ot which is fupplied by hornblende or 
ffeatite; and he reafons from the height of thefe moun¬ 
tains, which he fuppofes to have been elevated by fub- 
terraneous force from a great depth beneath the furface, 
that deeply-iituated granite in general contains very little 
mica; Hrengthening his conciulion by the fad, that thofe 
fragments of granite which are thrown out from volca¬ 
noes, and which may be fuppofed to have come from a 
great depth, contain very little mica. 
Sometimes the conHituent parts of granite are very dif- 
tindly cryHallized, particularly the felfpar. This is the 
cafe in the granite with which the foot-path of Weff- 
minffer-bridge is paved; which came, according to Mr. 
Smeaton, from Llanlivery, near Fowey, in Cornwall. At 
other times the cryHallization is extremely indiHind; fo 
that it is very difficult to afcertain the real nature of the 
rock, from its clofe refemblance to fome varieties of the 
Hone which in Scotland is called whin. Whoever has 
travelled in thofe parts of Scotland which abound with 
granite and whin, and has direded his obfervation to 
this fad, muH have had frequent opportunities of veri¬ 
fying it: and, partly in confequence of this great fimi- 
larity, Dr. Hutton fuppofes that granite, like whin, has 
once been in a Hate of igneous fuiion; and that, having 
been forced up from the deeply-feated mineral regions, 
it has elevated the flrata at the fame time. Mr. Playfair, 
from whom the foregoing oblervation is taken, addsjuff- 
ly, as it appears, that granite has evidently undergone a 
change from a fluid to a folid Hate ; as is evinced from 
the cryflallized Hrudure in which fome of its component 
parts are ufually found : and Mr. Gregory Watt has ren¬ 
dered it highly probable, by the refults of his experi¬ 
ments on bafait, &c. an account of which is contained 
in the Philofophical Tranfadions for 1804, that this fluid 
Hate was the confequence of Ample heat. He at leaff has 
done away one flrong argument againfl the fuppofition, 
by flrowing that in maffes which have been vitrified and 
cooled flowly, cryHallization adtually goes on after the 
mafs itfelf has been conloiidated : for, as from the mutual 
impreflion of the cryHallized parts it appeared that in 
fome inHances the leaff fufible were laft cryHallized, it 
feemed impolflble that this cryHallization could have 
taken place from a Hate of igneous fuiion. 
According both to Mr. Kirwan and Dr. Hutton, granite 
is almoff univerfally the balls on which other rocks, pri¬ 
mitive as well as lecondary, reff. It rarely contains me¬ 
tallic minerals; but of thefe principally tin and fome 
varieties of iron ore. Though extremely hard, it is ca¬ 
pable of being worked with tolerable accuracy by means 
of picks and wedges: and, according to Mr. Smeaton, the 
harder it is, the more accurately it can be worked. 
Although granite is the liardeff and one of the moff 
durable rocks we are acquainted with, it is, neverthelefs, 
fubjed to di/integration, which manifeffs itfelf not only 
in the crumbling of the furface of the expoled parts of 
granitic beds, but likewile in the leparation of vaff maffes, 
which, being difunited by the enlargement of the rents 
and fiffures that generally traverfe the granitic moun¬ 
tains, or qrofs the flrata in a nearly vertical diredion, are 
partly precipitated from their high fituation, partly dil- 
placed in various manners, fo as to produce the appear¬ 
ance of huge artificial ffrudures, and of other objeds to 
which the fancy of the beholder may compare them. M. 
de Luc has feen on the Rielenbirge, in Silefia, a number 
of pillars produced by fuch difintegration, both foiitary 
and grouped together, in a ffraight line, and, at a dii- 
tance, prelenting the appearance of many high piles of 
gourds. 
The Adon-fliolo mountains in Dauria, which confiff 
of granite, are, according to Pallas, in many parts broken 
into all manner of lhapes, reprefenting vaff ruins, grottos, 
and immenle flat maffes piled on one another in all di- 
redions*. 
