Siliceous Genus. 1 1 7 



hardnefs much greater than that of any other 

 ftone, and yields only to that of diamond ; 

 its fpecific gravity from 3,18 to 4*283. 



In fire it is invitriable per fe^ and does not 

 yield even to the focal rays of a burning glafs, 

 but a flame excited by dephlogifticated air, 

 directed by a blow-pipe, readily melts it ; it 

 does not lofe its colour in a heat that would 

 melt iron. Borax and microcofmic fait effet 

 its fufion, but mineral alkali fails. 





 100 parts of it contain, according to Mr, 



Bergman^ 40 of argillaceous, 39 of filiceous, 

 9 of mild calcareous Earth, and loof iron. 



Or, according to Mr. Achard^ 41,66 of 

 filiceous Earth, 36,66 of argill, 8,33 of cal- 

 careous Earth, and 10,83 of iron. 



Brazil rubies are paler, and faid to be found 

 in hexangular or polyangular cryftals. 







Jewellers, among whom hardnefs and tranf- 

 parency are the chief chara&eriftics, mention 

 alfo white and arnethyft coloured rubies, but 

 thefe have not been analyfed. 



Oriental rubies are chiefly found in Pegu, 



Ceylon, B!Jnagar> and Cambuya. A bafer fort 



I 3 is 



