Siliceous Genus. 129 



A reddlfh brown, prifmatic fhoerl of this 

 fort, from Ve/iivius, contained, according to 

 Mr. Bergman, 48 per cent, of filiceous Earth, 

 40 of argill, 5 of calcareous, I of magne- 

 fia, and 5 of iron* The ufual fluxes affedt 

 this fpecies, as they do the foregoing. 



The filamentous fort refembles afbeftos, and 

 differs externally only in tranfparency and 

 breaking with an even furface. 



II. VARIETY. 

 Opake. 



Thefe are of all colours, white, black, red, 

 brown, greenifh, and violet ; the filaments are 

 conjoined and parallel, or diverge, as from a 

 common center. Thofe of a fcaly or fparry 

 appearance are generally greenifh or black, and 

 are called Hornblende. i hey are frequently 

 cryftalized in regular forms, and often fo foft 

 as to be fcraped with a knife. 



100 grains of the black cryftalized fort 

 from Albano, afforded Mr. Bergman 58 of 

 filex, 27 of argill, 5 of calcareous Earth, i 

 of magnefia, and 5 of iron. 3 Bergm. 207. 

 Other forts have afforded 50 per cent, of fili- 



K ceous 



