Chemical Examination of American Minerals. 45 



These grains are translucent : some of them indeed are 

 transparent. The lustre of the transparent grains is splen- 

 dent ; that of the translucent grains shining. The lustre is 

 inclining to resinous. 



The grains are rounded, but when examined by the mi- 

 croscope, they seem to consist (>♦ imperfect crystals. 



The texture before a powerful magnifier seems foliated ; 

 but the grains are so small, that it is not easy to make out its 

 true texture with accuracy. 



Specific gravity 3'20I. 



Easily crushed to powder by the nail of the finger. It is, 

 therefore, soft. It does not scratch calcareous spar. 



Infusible before the blow-pipe per se. Nor did it fuse 

 along with carbonate of soda. The constituents were found 

 to be, 



Silica, ----- 32- 708 



Lime, ----- 36-308 



Alumina, ----- 12-280 



Peroxide of iron, - - - - 12-000 



Protoxide of manganese, - - - 3-680 



Water, - - - - - 0-600 



97-576 



If we were allowed to consider the iron and manganese as 

 accidental substances, the xanthite would be a compound of, 



2 atoms silicate of lime, - - - - 11-0 



1 atom silicate of alumina, - - - - 4-25 



15-25 



If the iron and manganese are considered as essential, then 

 a portion of the lime, or alumina, must be accidental ; other- 

 wise the mineral could not be considered as a chemical com- 

 pound. 



