C. U. Shepard, Sr.—Mineralogical Contributions. 91 
those of columbite or of tantalite. They are all strictly isomor- 
hous. An unimportant, though striking peculiarity is ob- 
served in these crystals, proceeding from the unusual develop- 
ment of the octahedral faces, whereb they possess a four- 
sided pyramidal summit at one, or each extremity. Very rarely 
are traces of the — plane visible; and when seen, the 
fe) pavonine tints are seen in the present variety. Their 
absence i sh so marked, not only on natural planes but also on 
fracture es, as to afford a ready an sure criterion 
for pterrmpertire ais specimens of this locality from those obtained 
at the old one of Brainards, where every crystal and almost 
every rns Sees displays the blue or yellowish tarnish. 
The color of the fracture is perfectly black ‘approaching 
pitchy. at is more firm, and less prone to crumble than the 
ordinary columbite. The fracture is occasionally small con- 
choidal. No distinction in hardness can be made out. It is 
nevertheless more easily ground to a fine powder than the 
usual mineral; and, when perfectly powdered, presents an 
almost black color, ‘while columbite is only brownish black. 
light distinction is so marked, as to be recognized by candle 
But the most remarkable distinction resides in its lower 
534 = 5°35; while four specimens of columbite from the 
B rd locality gave 6°02, 6°03, 6:10 and 619,—the average 
being 6-085. 
Its powder, strongly heated in an open platinum crucible, 
lost only ‘02 p. c. in weight but changed in color, by sey eral 
shades, to a brownish bla 
Alone before the blow- ar small fragments had their edges 
decidedly rounded by fusion. Treated in powder in small 
