154 DOMAIN 11. SILICEOUS. 



Petrosiiex. anc | thepetrosilev of their writers in Latin - 9 which 

 has of course been confounded with the petro- 

 silex of the Swedes and French, which is com- 

 pact felspar. To avoid this confusion the Greek 

 term keralite has been adopted, from Lametherie. 

 Keralite is not fusible by the blow-pipe, but 

 compact felspar generally is. It is also often 

 found impregnated with metals, while compact 

 felspar or felsite has perhaps never been observed 

 to attend metals. Felsite also presents the va- 

 rious colours of felspar; while keralite chiefly 

 passes from white, through grey, to black. It 

 may be regarded as an impure quartz, and 

 shares the sites and properties of that substance. 

 In England it is called chert, and often runs 

 in veins or layers through lime-stone, particu- 

 larly in Derbyshire. 



STRUCTURE I. MASSIVE. 



Aspect 1. Common. Bluish grey rock-flint, 

 sometimes mamellated, and approaching to chal- 

 cedony, from the lead-mines of Bretagne. This 

 is properly a vein-stone ; and Brongniart has ob- 

 served, i. 355, that such are hornsteim, though the 

 appearance be waxy, as they are infusible. Fel- 

 spar or felsite rarely appear as vein-stones. 



Of a lighter grey, with blende and galena, from 

 the same. 



