71 



TAB. CXXXVIII. 



This is a harder specimen than the former, and much 

 about the .density of common Caout-chou. It is some- 

 what remarkable for its peculiar conchoidal fracture, on 

 the faces of which, when minutely examined, peculiar 

 risings occur, bounded by curved lines crossing each other, 

 and terminating in a kind of centre not unaptly re- 

 sembling the fracture of Carbonate of Lime with a kind of 

 curvilinear crystallization * ; the cracks seem not at all 

 guided by this. The elasticity is something like the former, 

 as it soon separates if we endeavour to stretch it out. It is 

 externally of a blooming gray, and internally of an olive 

 green colour. This is oozing more or less from different 

 parts of the gangue, which is a mixture of Carbonate of 

 Lime, Galena, &c. Some of the smaller particles have a 

 reddish illinition in their flaws. 



* I have lately received a fine specimen of Carbonate of Lime from 

 Mr. Hall of Arkendale, very expressive of this. 



