Earths. MINERALO G Y. Earths. 
460 
tion. Bruce mentions an Emerald Kland in the Red Sea ; 
but lays that the green fubftance he there met with was 
fcarcely harder than glafs. May not this have been a 
chryfolite, and this illand the Topaz Ifland mentioned 
by Pliny ? Jewellers have created much confulion with 
refpedt to the identity of the chryfolite; having applied 
the term to many different fubltances, from a mere refem- 
blance in colour. $ 
14. Gemma fmaragdus, the emerald : hard, pellucid, 
lightilh, grafs-green, when heated to 123 of V/edgewood 
becomes blue, but recovers its green colour when cold ; 
melting before the blowpipe, of a conchoidal texture. 
Found in the mountains of Egypt and Ethiopia, in Peru, 
Ruffia, and the confines of Perfia. ‘ Colour from the per¬ 
fect to the pale grafs-green. Cryltals hexagonal prifms, 
either perfect or truncate on the angles and edges, termi¬ 
nating in truncated pyramids; texture foliated; frafture 
conchoidal; becomes eleftric by fri&ion, but not by heat; 
caufes a double refraction; melts into an opake-coloured 
mafs at 150 0 of Wedgewood. Specific gravity, z"j. Con¬ 
tains iilex 64'6, alumine 14, glucine 13, cxyd of chrome 
3'5, lime moilture or other volatile ingredient 2. 
This is the analyfis more particularly of the emerald of 
Peru, from which it appears, that this emerald of Peru 
only differs effentially from the beryl by containing an 
oxyd of the metallic fubftance called chrome. It is fup- 
poled that the more lively hue of the emerald is owing to 
the peculiar nature of the metallic fubftance by which it 
is coloured. 
Emeralds are laid to have been found in Afia, particu¬ 
larly in Ceylon ; and in Egypt; but it is doubtful whe¬ 
ther a ftone of the fame fpecies with the Peruvian eme¬ 
rald, that is, containing at the lame time glucine and oxyd 
of chrome, was known before the difcoveiy of America. 
Tavernier fays, that the emerald is an occidental gem, 
imported from America to the Philippine illands, and 
from thence into Europe. That which is called the Ori¬ 
ental emerald, and which differs from the Peruvian not 
lefs in its l'uperior degree of hardnefs than in the nature 
of its conftituent parts, is a green variety of the fapphire ; 
and of this nature probably is the gem of the late arch- 
bilhop of York, mentioned by Dr. Vincent in his Hif- 
tory of the Commerce and Navigation of the Ancmnts. 
This gem, engraved with a Medula’s head of Grecian 
fculpture, was brought from Benares. The table in the 
abbey of Reichenau near Conftance, faid to be of eme¬ 
rald, was afcertained, by Mr. Coxe to be green fluat of 
lime. The famous cup long preferved at Genoa under 
the name of &aero Catino, and now in polTeftion of the 
French, is upon good grounds conlideredas nothing more 
than green glafs. 
It is not eafy to conjecture what was the nature of the 
fmaragdus of the ancients : Pliny fay's that it poflefied the 
molt vivid of all green colours ; and this probably might 
be faid at his time of the oriental emerald; but it may 
be inferred from the follow ing palfage that the fmaragdus 
was too commonly uled, and its dimeniions too large, to 
juftify the fuppoiition of its being that fubftance. Speak¬ 
ing of the fmaragdus he lays, Scalpentibus gemmas non alia 
gratior cculorum rtfaCtio eji: ita <viri dilenitate lafttudinem 
mulcent. Now the emerald is rarely of any conliderable 
magnitude, and at the fame time perfectly clear and free 
from lpots. It poflefles the fame diltinCtive marks of cha¬ 
racter as the beryl. The refemblance between them in¬ 
duced Wallerius to clafs them under the lame head be¬ 
fore the correfpondence in their phyllcal and chemical 
characters had been afcertained. Werner however ltill 
conliders them as diftinCt fpecies. 
The emerald is found in confiderable abundance in 
Peru, between the mountains of New Grenada and of 
Popayan, in the clefts and cavities of lchiftofe and gra¬ 
nitic rocks. Count Bournon met with cryltals of eme¬ 
rald in France, in a part of the fame rock where he found 
lap]Tires. Brochant fays, that Dolomieu found a trans¬ 
parent and colourlefs emerald, in granite, in the ifle of 
Elba. 
15. Gemma foranus, or hyacinth-garnet: hard, pellu¬ 
cid, lomewhat ponderous, foliated, of an hyacinth colour, 
which is permanent in a moderate heat, eafily melting in 
a ftrong heat into an opake lpumid mafs. Found in Swif- 
ferland, Norway, Greenland, and the mountains of Sibe¬ 
ria ; alfo in Brafti and Ceylon ; fometimes in the form of 
rounded grains mixed with fand or earth, fdmetimes im¬ 
bedded in other Hones, in lix-lided cryltals terminated on 
each fide by a three-lided pyramid. It is twice as hard as 
fpar, and lofes its colour when fprinkled with the ftronger 
mineral acids. 
16. Gemma granatus, the garnet: hard, ponderous, 
red, of unequal texture; prelerving its colour in a low 
heat, melting in a ftronger heat into a brown opake fpu- 
mid mals. There are about fifteen different varieties, 
diftributed throughout Great Britain, Bohemia, and va¬ 
rious parts of Europe ; Madagafcar, Ethiopia, India, Sirian 
in Pegu, &c. fometimes in mafs, fometimes cryllallized, 
in innumerable varieties of black, brown, purple, red, 
green, and yellow: texture foliated: fraCture commonly 
conchoidal: luftre glafly and waxy. The colour molt 
efteemed in the garnet is red: but it is met with of va¬ 
rious other colours; yellow, green, brown, and black. 
Its fpecific gravity varies from 3*55 to 4-18. Primitive 
form, a dodecahedron w’ith rhomboidal faces, all of which 
are fimilar and equal. This form, which correfponds 
with that of the cells in a bee-hive, comprehends the 
greateft capacity under the fmalleft extent of furface. The 
effentially-conftituent parts of garnet are filex, alumine, 
lime, and oxyd of iron ; but the proportions ofthefe vary 
confiderably in the different varieties: viz. filex from 34 
to 52, alumine 6 to 28, lime o to 71, oxyd of iron 10 to 
36 ; but the Sirianic and Bohemian garnet, which are 
moft valuable on account of their tranfparency and co¬ 
lour, contain a greater proportion of iron than any of 
the other varieties : the yellow and black garnet, a greater 
proportion of lime, and a lefs proportion of alumine. It 
appears all’o, as indeed might be expefted, that the fpe¬ 
cific gravity of garnets is heightened in proportion to the 
quantity of iron contained in them. 
The oriental or noble garnet, as it is alfo called, is 
faid to be of a crimfon colour; the Bohemian, rather cf 
a blood red: but it ftiould be obferved that the term 
oriental has a reference rather to beauty and hardnefs, 
than to local fituation. The Bohemian garnet would in¬ 
deed by jewellers be called oriental in preference to any 
other; being of a greater degree of, tranfparency: hence 
indeed it is moft frequently ufed in jewellery. In/ome 
inftances the colour is fo intenfe, that, to facilitate the 
difplay of this, it is cut into a form fomewhat refembling 
the cup of an acorn, but more flattened. The Bohemian 
garnet is found, together with hyacinths and iapphires, 
in alluvial diftrifts, which appear to have been formed 
by the detritus of bafaltic and ferpentine mountains. 
Small Bohemian garnets,, when pulverized, are fometimes 
ufed as emery. Garnets are met with in moft parts of 
the world; principally in gneifs, and rocks of the mag- 
nefian genus. They are very common in the highlands 
of Scotland, and are difteminated in pryftals through the 
fubftance of varieties of gneifs and granite. But fome 
fpecimens from that quarter confift of fmall dodecahedral 
cryftals, of a blackilh-red colour, and about the fize of a 
pea, loofely cemented together by a dark-coloured fub¬ 
ftance bearing no proportion in quantity to the garnets 
themfelves, which conftitute more than nine-tenths of the 
whole mafs. Some remarkably-large cryftals of garnet 
are met with in the mountains that fepayate Stiria from 
Carinthia: they are incrufted with green talc. Equally 
large cryftals are found in the Tyrol; but without this 
incruftation of talc. Some of theie large cryftals are of a 
dark reddilh-black colour, and capable of receiving a po- 
liih lufliciently fine to reflect the image# of objeifts from 
their 
