Siliceous Genus. 1 2 1 



jnild calcareous Earth, and 2 of iron ; and 

 Mr. Achard 58,33 of argill, 33,33 of filex, 

 6,66 of calcareous Earth, and 3,33 of iron. 



Jewellers mention white, green, and yel- 

 low fapphires, or pale red. 



SPECIES VII. 

 Amethyji, 



Some of this fpecies are as tranfparent as 

 the former ftones, others duller ; its fpecific 

 gravity, which reaches only from 2,6 to 2,7, 

 makes me judge it to be very different from 

 them > its colour is pale bluiih red ; its tex- 

 ture nearly granular, and generally cryfta- 

 Jized in hexangular prifms ; it lofes its colour 

 in a ftrong heat, but does not melt per fe y 

 though with borax it gives a colourlefs glafs ; 

 its cornpofition has not yet been examined. 



SPECIES VIII. 



Siliceous Earth united to T ' T of its weight of 

 Calcareous Earth^ ftilllefs of Magncfta, 'with 

 an exceeding fmall Proportion of Iron, Cop- 

 per, and Sparry Acid. 



Chryfoprajinm. 



It is of an apple green colour, and femi- 

 tranfparent; it has never been found cry- 



ftalized . 



