264 Dr T. THOMSON'S Account of the 



Not scratched by quartz, and scarcely by topaz, but easily by 

 sapphire. 

 Brittle. 

 Easily frangible ; fragments sharp-edged. 



Specific gravity 3.193. 



It was analysed by Messrs HILTON and MITCHELL, and its 

 constituents found to be, 



Silica, 46.40 



Alumina, .... 52.92 slightly tinged with iron. 



99.32 

 BRANDES'S analysis gave 



Silica, ... ... 46 



Alumina, 50 



Protoxide of Iron, . . , .... , 2.5 

 Potash, 1.5 



100 



It is clear from the analysis, that the American specimens ana- 

 lysed in my laboratory were much purer than those in the pos- 

 session of Dr BRANDES. 



Bucholzite is obviously a silicate of alumina, or a compound 

 of 



1 atom silica, .. 2 ... or 46.4 

 1 atom alumina, . 2.25 .... 52.2 



numbers which approach very nearly to the result of the analysis. 



13. Calcareo-sulpkate of Barytes. 

 This mineral occurs pretty abundantly in the lead-mine of 



