532 PITCHSTONE. 



It must here also be remarked, that notwith- 

 tanding its vitreous aspect, it often contains a 

 great deal of loose water, which is easily sepa- 

 rated by drying, as in many other rocks. In 

 these cases it is tender, but becomes brittle after 

 the water has evaporated. 



In many cases, pitchstone possesses an uni- 

 form structure, showing no tendency to particular 

 forms of any kind. In these, the. fracture is flat, 

 or more or less perfectly conchoidal, or sometimes 

 doubly conchoidal, one concave fracture being 

 contained within another. It is, occasionally also, 

 minutely splintery at the same time; and very 

 often the flat, or conchoidal fractures, are on so 

 small a scale, and so various in position, as to 

 produce an irregular angular surface. 



The lustre of pitchstone varies exceedingly 

 according to its several states or varieties ; pass- 

 ing from the most perfectly vitreous to one 

 scarcely more glossy than that of the finest ba- 

 salts. 



The colours are various ; but a detailed ac- 

 count of them being given in the Synopsis, they 

 need not be noticed here. In Scotland the 



