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PITCHSTONE. 



This rock is either simple, or porphyritic, or 

 spheroidal concretionary, (as in pearlstone) ; but, 

 in every case, it may be recognized by its smooth 

 glossy fracture when simple, or by that of the base 

 when it is compounded. The lustre is more pro- 

 perly like that of broken pitch than glass, and it 

 could only be confounded with obsidian ; a mi- 

 neral strictly volcanic, and otherwise distinguish- 

 able by its almost absolute identity with the 

 glasses formed in metallurgic operations, and by 

 other characters to be found in systems of mine- 

 ralogy. 



OCCASIONAL ROCKS. 



JASPER. 



The brilliant or varied colours of this rock, 

 either mixed or simple, form its most ostensible 

 and convenient distinction. These are, however, 

 chiefly reds, of various hues, and yellows. The 

 lustre is sometimes equal to that of pitch ; m 



