466 



ON CRYOLITE 



to Klaproth and Vauquelin, who also found it t# 

 contain alumina and fluoric acid ; but natron in 

 place of potash. It appears, from the analyses of 

 these consummate chemists, that this remarkable 

 fossil contains from 40 to 47 per cent, of fluoric 

 acid and water ; from 32 to 36 per cent, of soda } 

 and from 21 to 23 per cent, of alumina. Its ex- 

 ternal characters have been given by different na- 

 turalists, but not with sufficient minuteness ; and 

 its geognostic relations have hitherto remained un- 

 noticed. Through the politeness of Colonel Im- 

 rie, who presented me with several specimens of 

 this rare mineral, I have been enabled to draw up 

 a description of its external aspect, and to ascer- 

 tain its accompanying minerals ; and from these to 

 infer, with some probability, the kind of reposito- 

 ry in which it occurs. 



EXTERNAL CHARACTERS. 



Its colours are greyish- white, and yellowista- 

 grey. * ^u* rU7r -'-. >.yrVM 



It occurs massive, disseminated, and in cubical 

 pieces. 



Its internal lustre is vitreous ; and is shining in 

 one direction, but only glistening in another. 



Its fracture is imperfect foliated, with a three- 

 fold rectangular cleavage. 



The fragments are cubical, or tabular. 



