160 



DOMAIN II. SILICEOUS, 



Characters. 



Palaiopetre. 



Petrosilex of 

 Wallerius. 



MODE IV. FELSITE, OR COMPACT 

 FELSPAR. 



Texture, compact. 



Hardness, felsparic. Fracture, minutely fo- 

 liated. Fragments, rather sharp, amorphous. 



Weight, granitose. 



Internal lustre, glimmering, or glistening. 

 Translucent, sometimes only on the edges. 



Colours, various, as of felspar, which may also 

 distinguish it from keralite. Melts under the 

 blow-pipe. 



It is doubtful if it form entire mountains; but 

 is an important rock, and among the most pri- 

 mitive. 



It is the Palaiopetre of Saussure, who found it 

 near the summit of Mont Blanc ; and a speci- 

 men which he sent to Lametherie, and which I 

 have seen, is compact felspar, easily fusible by 

 the blow-pipe. 



It is the petrosilex of Wallerius, and in conse- 

 quence of the Swedes and French; so that it 

 must be carefully distinguished from real petro- 

 silex, which literally implies the rock-flint of the 

 Germans, being a modification of quartz, and 

 not of felspar. The name felsite was very pro- 



