Siliceous Genus. 131 



SPECIES XV1L 



Siliceous Earth imperfeflfy united 'with from 

 1,05 to 1,47 of its weight of Argill, from 

 0,3 to 0,4 of its weight of mild Calcareous 

 Earthy and from 0,15/0 0,243 f* ts wn&bt 

 of Iron* 



Tourmaline. 



Tourmaline has hitherto been found only in 

 Ceylon^ Brazil^ and the Tyrol. A fpecimen of 

 each has had the advantage of having been 

 particularly examined by Mr. Bergman. That 

 of Ceylon is of a dark brown, or yellowifh 

 colour, its fpecific gravity 3,065, or, 3,295; 

 that of Brazil is green, blue, red, or yellow, 

 and its fpecific gravity 3,075 or 3,180 ; that 

 of Tyrol, by refle&ed light, is of a blackilh 

 brown, but by refrafted light, yellowifh, or 

 in thin pieces, green; its fpecific gravity 

 3,050 ; moftiy Ciyftalized in polygon prifms, 

 but fometimes amorphous. The thickell 

 parts are opake : the thin more or lefs tranf- 

 parent. 



All are electric when heated to about 200 

 of Fahrenheit. Their texture is lamellar, 

 and their furface has a glaflfy appearance. 



In fire none of them decrepitate ; but 



thofe of Ceylon and Tyrol melt perfe into a 



K 2 black 



