174 DOMAIN ii. SILICEOUS. 



coarse-splintery, fracture, and bursts into thick 

 slaty fragments. The edges of its thin splintery 

 fragments are transparent. It is pretty hard, and 

 at the same time considerably tenacious. When 

 triturated, it yields a light grey powder. 

 " Its specific gravity is 2,575. 

 " The lamellae of a greyish white, strongly 

 splendent felspar, which are interspersed in its 

 smbstance, together with the very minute crystals 

 of a black hornblende, give to it the character of 

 porphyry."* 



The result of the analysis is 



" Silex 57,25 



Alumine .... 23,50 



Lime 2,75 



Oxydofiron ... 3,25 

 Oxyd of manganese 0,25 



Soda 8,10 



Water 3 



98,10 



" The reflecting natural philosopher will know, 

 without my suggesting it, how to appreciate the 

 value of this discovery of the presence of soda, as 

 a constituent part, in a stone which occurs in 

 masses of the size of entire mountains. It opens 



* Klaproth Anal. Essays, ii. 182. 



