103 



TAB. CCCLVI. 



S I L E X piceus, 

 Glassy Pitchstone. 



Class 2. Earths. Order 1 . Homogeneous, 

 Gen. 4. Silex. Spec. 7. Pitchstone. 



Syn. Pitchstone. Kirw. 1. 292. 

 Pechstein. EmmerL 1. 262. 

 Petrosilex resinite. Haily, 4. 386. 



l hese Stones are so like Pitch in general, that no one 

 could mistake them, except when they vary in colour and 

 have a glassy appearance, as is sometimes the case. The 

 fracture in some fine specimens is large, concentric, sharp, 

 and conchoidal, in others more splintery. We figure one 

 of the latter, which includes Petuntse, or Feldspar, and al- 

 so has more or less of a glassy appearance. This, taken 

 in the whole, would be called Pitchstone Porphyry. It 

 came from Arran in Scotland, and contains Alkali. Hence 

 it nearly approaches common glass. 



Quartz is so extremely likely to vary in its appearance, 

 especially when chemically combined with colorific or 

 other matter, that it may be considered as liable to as many 

 varieties as any other known substance. Thus it varies 

 from Calcedony or Agate, to Cachalong and the various 

 Opals : — see tab. 111. and also to Jasper, wax-like Horn- 

 stone, Flint, and even Pitchstone. Under the term Pitch-; 

 stone may be included those siliceous stones which are fu- 

 sible and resemble glass, as they can sqarcely be separated 

 but by fancied differences (as the usual appearance of Pitch. 



