DOMAIN II. SILICEOUS, 157 



MODE III. FELSPAR. 



Texture, strait, foliated. Characters. 



Hardness, of course felsparic. Fracture, la- 

 minar. Cross fracture, fine-grained, uneven, 

 approaching the splintery. Fragments, sharp, 

 rather rhomboidal. 



Weight, granitose. 



External lustre, shining ; of the cross fracture, 

 glimmering, glassy, sometimes pearly. Trans- 

 lucent. 



Colour, many varieties of white, grey, green, 

 and red ; rarely blue or black. 



It often composes mountains, especially when 

 interspersed with mica; and is the most abundant 

 substance in granite, where it often forms distinct 

 crystals *. 



There are mountains and large strata of fel- 

 spar in the north of Scotland. 



* It is sometimes classed with the Argillaceous, because some 

 kinds decompose into clay ; yet this effect probably arises from the 

 potash. But it forms the chief part of granite, which has never 

 been classed among argillaceous substances. 



According to Lametherie, v. Q, felspar requires the most water 

 to crystallise, so must be the most ancient ; and is followed by horn- 

 blende, quartz, mica, magnesia, and the metals successively. But 

 the grey petrosilex of Vosges is a felsite. Ib. 352. 



