14^ On Crystallized JVative Terrestrial Iron, ^c. 



have been easy to detect the arsenic by its odor ; the common blow- 

 pipe being insufficient, on account of the feeble proportion in which 

 it exists, to render it obvious in either the North Carolina, or the 

 Pennsylvania specimens. 



In the mass examined from Pennsylvania, which formed a part of 

 a regular crystal, (the base being somewhat elongated, and the sum- 

 mits obliterated,) I suggested that it might belong to the class of rhom- 

 bic prisms ; an opinion which I am now happy in having an opportu- 

 nity to rectify. The larger angle then obtained, overlooking the 

 error of one degree in the measurement, it is obvious, belongs to the 

 base of the octahedron ; while the smaller angle of 59° correspond-s 

 to the angle over the summit of this figure. 



2. Ferro-silicate of Manganese. 



I am about to announce the existence of the present species in 

 mineralogy, (recently established by Dr. Thomson,) in Cumberland, 

 Rhode Island ; with some farther information concerning its crystal- 

 lization, than is given in the original description : but as an account 

 of this mineral is not yet to be found in any system of the science, 

 and has not been noticed in this Journal, I shall first abstract from 

 the original memoir, published in the " Annals of the Lyceum of 

 Natural History of New York," (Vol. III. p. 28.) the substance of 

 Dr. Thomson's description, and then append to it the remarks pro- 

 posed. 



Color brown, with a shade of red ; externally, it is dull, having an earthy aspect 

 and may be scratched by the nail ; but internally, it is foliated, splendent, of a grey 

 color, with a shade of red ; hardness nearly the same as felspar : specific gravity 

 3.44. 



It has three cleavages, indicating a doubly oblique prism for its primitive form. 



P on M - - - - 108° 



P on T 86.30' 



M on T - - - - 86.30' 



The faces not being smooth or flat, these measurements are only given as approxi- 

 mations ; and on the examination of another crj^stal. Dr. T. suggests that the pri- 

 m'ary form may be a right oblique prism. 



A portion of the mineral was treated with muriatic acid, till it assumed a white 

 color. Much chlorine was evolved, and nearly one fourth of the mineral wps dis- 

 solved. The solution a:avr 



