Chemical Examination of American Minerals. 51 



Silica, _ - _ _ - 



Magnesia, _ _ _ _ - 



Alumina, _ _ _ _ - 



Protoxide of iron, . _ - - 



101-69 



If the alumina and protoxide of iron be only accidental 

 substances, then the constituents of the mineral are, 



2 atoms silica, _ _ _ - _ 4 



1 atom magnesia, - - - - - 2-5 



6-5 



The constituents of picrosmine, as determined by Mr. 

 Magnus, are, 



Silica, ------ 54-886 



Magnesia, - _ . _ _ 33'34S 



Alumina, . . _ . _ 0-792 



Protoxide of iron, - - _ _ 1-399 



Protoxide of manganese, _ _ _ 0-420 



Water, ------ 7-301 



98-140 



The chief difference between the mineral described by 

 Haidinger from Bohemia, and the American mineral, consists 

 in the former containing 7-301 of water, while the latter is 

 anhydrous. The specific gravity of Haidinger's mineral 

 (owing to the water) is only 2-66, while that of the American 

 mineral is 2-970. I have little doubt that they will be found 

 ultimately, to be only varieties of the same species. 



17. HYPERSTHENE. 



The three mineral species, jnjroxene, amphibole, and hyper- 

 sthene, have considerable analogy both in their situation and 

 i^omposition. Thev all occur as constituent? of trap rocks. 



