32 Chemical Examination of American Minerals. 



By another analysis they obtained, 



Silica, 25-00 



Oxide of zinc, - - _ - _ 71*33 



Oxide of manganese, _ - _ - 3*66 



Oxide of iron, - _ _ _ _ o*67 



Loss, -_-.-_ Q-34 



100-00 



These gentlemen supposed its primitive form to be a rhom- 

 bic dodecahedron, while that of the ordinary electric calaminci, 

 is a hexahedral prism. 



Dr. Troost, so justly distinguished for his attainments in 

 crystallography, states that the nucleus of this mineral is a 

 cube. He proposed to consider it as a distinct species.* 



It occurs crystalized in regular six-sided prisms, termina- 

 ted by low three-sided pyramids. The faces and edges of 

 the pyramids are imperfect, as if they had undergone partial 

 fusion or solution, so that their angles cannot be determined 

 with accuracy. The faces, however, appear to be inclined 

 to each other at an angle of 120°, indicating the primitive 

 form to be a cube, and the secondary a rhombic dodecahe- 

 dron. 



Sometimes the crystals occur six or eight inches in length, 

 and two or three inches in diameter, but occasionally they 

 are found very slender. They yield with considerable diffi- 

 culty to cleavage. 



6. SESQUISILICATE OF MANGANESE. 



The mineral, to which from its composition 1 give this 

 name, was contained in a specimen sent me about two years 



Journal of the Philadelphia Academy, Vol. IV. p. 220. 



