Diamond. 157 



APPENDIX I. 



Of Diamond and Plumbago. 



Thefe fubftances cannot well be arranged 

 under any of the clafles of minerals ; not 

 under that of Earths as they contain no 

 Earth, nor under that of inflammables, as 

 their inflammability commences in fuch high 

 degrees of heat, and is fo gradual that it can 

 fcarcely be remarked but by its effecl: in dimi- 

 niming the weight of thefe fubftances after 

 a long expofure to fire ; fo that they differ 

 intirely from all other inflammables, whence 

 I think it convenient to treat of them a part. 



Diamond. 



Diamond is always tranfparent, and moftly 

 colourlefs, but fometimes tinged, yellow, 

 reddiih, green, blue, or brown; it is fome- 

 times externally, but always internally bright ; 

 it is generally cryftalized in oclohedral cryftals , 

 but fometimes found in round mafles : its 

 texture is lamellar. 



It ftrikes fire with fteel, cuts the hardeft 

 cryftals, and even rubies, being the hardeft 

 of all bodies : its fpecific gravity is from 3,5 

 to 3,66. 



No 



