EARTHS. SILICEOUS. 42. Gemma. 
143 
Found in Bra 0 , the Indies, Perfta, Bohemia, and near Pays ia 
Velaf, fometimes cryftailized, fometimes in rounded maffcs, 
the angles being worn off by friftion, and is next in value to 
the Ruby: colour Iky-blue, or the (liades of Pruffian and 
indigo-blue, with fometimes white fpecks: the cryttals arc. 
ftrong, Ihining, and exhibit a foliated texture traufvcrfely 
ftriatc; they become colourlefs when hea ed with micro- 
cofmic fait, and emit a great light while burning : fpecific 
gravity from 3,780. to 4,000. contains alumina 58. filica 
35. carbonate of lime 0,5. irono,z. Biergmasi. 
^opazius. Nearly very hard, ponderous, yellow, of a foliated tex- 
ture which is conchoidal when broken tranfvoffcly, 
not fufible per fe, but lofing all its colour in a llrong 
heat- 
Borax Topazius. S^Ji, nat, xii. 3. /• 94 
Gemma pellucidiflima. Wall. fyst. 1. p 239. ». 4 ’ 
Oriental Topaz. Kirnuan mineral. 1./. 251. 
Topaz. BcbmeiJJer mineral i. p 62. 
Iniperfeft Corundum. Tbomjonchem 3. /. 505. 
Found in India, Brafil, RuJJia, Saxony, Bohemia, Sic. gene- 
rally adhering to. other fubftances, though fometimes de- 
tached with the angles worn off" : colour a lighter or deeper 
yellow, moft commonly honey-colour, fometimes verging to 
white or greenilh; its fragments are fometimes irregular, 
fometimes granular or prifmatic : ths prifms longitudinally 
ftriate, folitary, in pairs, or in threes difpofed in a cruciate 
manner, often cluftered, rarely 4-fided, rcflangular or ob- 
liquangular, more frequently unequflly 8-fidcd term nated 
by an irregular 4 or 8-fided pyramid, or ending in a point: 
is infufible per fe, and lofes its colour only in a vert high de- 
gree of heat : melts with borax and microcofntic fak into a 
clear glafs: fpecific gravity from 3,531. to 3,564. contains 
filica 52 alumina 44. carbonate of lime 2. oxyde of itoa 
0,31. Bergman. 
^lactnthus. Hard, lamellar, of a peculiar yell owidi -red, in 4-rided 
prifms terminated both fides by a 4 fided pyramid, 
not fufible per fe, but lofing its colour in a ftrong 
heat. 
Nitrum lapidofuin. Syst nat, xii. 3./. 85. n. 3. a. 
Topazius ftave-ruben.'. Wall. fit*. 1 . />. 240. «. 4. I. 
Hyacinth Kimxtn ndne al. i.p 257, 
Zircon, Jargon, Hyacinth. ‘Ihomjcn clem. %. p. 
Hvseinth, Schme jer msneral.l p 64. 
Found in the Faff and Bohemia, m the form of pebbles, in oh- 
tu'e angular p,ci.es : colour ye’b ' ilh red with a mixture of 
brown; the cry Hal* are fmall, have a fuiuoth furfacc and 
