28 Chemical Examination of American Minerals. 



Note. This mineral is not scarce at Franklin. It is gene- 

 rally associated with the red zinc ore and massive Franklinite* 

 Having recently examined its crystallographical characters in 

 same perfect specimens, I think its primitive form is a rec- 

 tangular prism, with slightly oblique bases. 



4. FERRO-SILICATE OF MANGANESE. 



I received the mineral, which from its constituents, I liiave 

 distinguished by the name of Ferro-silicate of manganese^ 

 from Dr. Torrey, under the name of Manganesian feldspar. 

 It comes also from Franklin, in New-Jersey. Dr. Torrey 

 informed me that it had been distinguished in a recent cata- 

 logue of North American minerals,* as Crystallized siliceous 

 oxide of manganese. He stated, that " if small fragments of 

 the mineral be boiled in muriatic acid, much chlorine is 

 evolved, and the fragments become light colored, but retain 

 their form. They then resemble felspar, though the angles 

 are different, and approach those of albite ; but it is not that 

 mineral. There appears to be much peroxide of manganese 

 diffused through it, though it contains also a pretty large 

 proportion in combination." 



The color of this mineral is brown, with a shade of red. 

 Externally it is dull, and has an earthy aspect, and may be 

 scratched by the nail. But internally it is foliated and splen- 

 dent, and of a gray color, with a shade of red, and is too 

 hard to be scratched by the knife. Its hardness when fresh, 

 is nearly the same as that of felspar. 



A threefold cleavage may be perceived in it, indicating a 

 doubly oblique prism for its primary form. P 

 makes on M an angle of 1 08°; P on T an 

 angle of 86^^ 30' ; M on T an angle of 86° 30'. 

 But these measurements are only approxima- 

 tions. The faces were not sufficiently flat nor 



* Robinson's Catalogue, p. 298. 



