4* A SYSTEM OF 



Pott has ingenioufly begun, as a bails for his 

 Lithogeognofia. For want of this, there is no 

 other way left, than to confider thefe bodies as 

 fimple fubftances (how much foever compound- 

 ed they may be), in the following manner. 



SECT, XLII. 



A. Diamond, Adamas gemma, 

 Which, 

 i. Of all ftones,. is the harder!. 



2. Is commonly clear, or tranfparent ; which: 

 quality, however, may, perhaps, only be- 

 long to its cryftals, but not to the rock it- 



• felf from which they have their origin. 



3. Its fpecific gravity is neareft 3,500. When 

 brought to Europe in its rough ftate y it is 

 in form either of round pebbles, with 

 mining furfaces, or of cryftals of an oc- 

 toedral form *. 



a. Colourlefs, or diaphanous, or the dia- 

 mond properly fo called. 



But it alfo retains this name when it 

 is tinged fomewhat red or yellow. Be- 

 ing rubbed, it difcovers fome electrical 

 qualities, and attracts the maftic. 



* The diamonds commonly cryflallize into ocloedral 

 forms, which, however, often are found fomewhat irregular, 

 efpecially when the furface inclines to cryftallize, during the 

 fhooting of the whole cryftal, and alfo when feveral of them 

 unite together into a groupe; in which latter circumftance 

 the one hinders the other from afluming its regular form ; 

 and of this I have (een feveral inftances. But the o&oedral 

 is not the only regular form which the diamond affumes ; I 

 have lately feen a rough diamond, or in its native ftate, in a 

 regular cube, with its angles truncated or cut orF. E. 



SECT. 



