On Crystallized JYative Terrestrial Iron, fyc. 14S 



Detoxide of Manganese, . . . 



Peroxide of Iron, - . - . 



The residue, which became white, was composed of 

 Silica, --.-.. 



Protoxide of Manganese, - . - 



Peroxide of Iron, . . . . 



Moisture . . . . - 



17.716 

 6.480 



29.480 



34.640 



6.740 



3.170 



98.226 

 Dr. Thomson supposes the mineral to have undergone a species of decomposition 

 externally, from the action of the air ; the protoxide of manganese having been con- 

 verted into deutoxide ; and originally, that the minei-al must have been a compound 

 of four atoms silicate of manganese, and one atom persilicate of iron. 



The specimens examined were obtained through Dr. Torrey, from Franklin, New 

 Jersey ; v/here this mineral has long been known to exist under the denomination 

 of the Crystallized siliceous oxide of Manganese. 



The Ferro-silicate of Manganese, I found in Cumberland some 

 years ago, at the same time I discovered the Yenite.* Both of 

 these minerals occur, engaged in the same gangue, and were for a 

 long time considered by myself, as identical, in consequence of an 

 early blow-pipe experiment which I made upon them, — both fusing 

 with equal ease into a black, shining globule, attractable by the mag- 

 net ; though the former I had not then met with, except in massive 

 specimens. Afterwards, observing that it invariably appeared distinct 

 from the Yenite, though accompanying it upon the 'same specimen, 

 that it possessed a distinct threefold cleavage, and, moreover, a hard- 

 ness above that of Yenite, I ceased to consider it any longer as such, 

 and placed it among my specimens of doubtful minerals. 



Lately, however, my attention has been called to it by a specimen 

 of the same substance, ticketed " Yenite," in a case of minerals pre- 

 sented to the American Geological Society, by the late Dr. Robin- 

 son. It was distinctly crystallized, and under a form quite incom- 

 patible with Yenite. The crystals consisted of parallel rows of short, 

 thin, obhque angled prisms, traversing the mass, and leaving chan- 

 nels between them. The largest of these did not exceed one fourth 

 of an inch in length, one fifth in height, and one tenth in breadth. 

 Their form is exhibited in the following diagram. 



P on T - - 85° f^ — r-V-^- 



k 



on T 

 on P 



Vide this Journal, Vol. VII, p. 25 1. 



