Unknown stone/gem from mine near Superior,MT

Dug this up on a gold claim about 8 miles south of Superior, MT. About 8 ft deep, in mostly sandstone and mud. It's a little smaller than a pomegranite seed, Black, with a rust colored vein on the outer surface. I can't seem to figure out the crystal pattern in a search that matches. It is almost perfect 12 sided, and the facets are perfect 5 sided. Thanks in advance if you can offer suggestions. I've been told by two people it looks like a black garnet.

Its most likely a tarnished or altered pyrite pyritohedral crystal

Well, this crystal has 12 faces just like a garnet, but there is a major difference: these faces are pentagons while these of garnets are diamonds.

This is a hematite coated pyrite.

Looks like a pyrite crystal to me (do a search for a "pyritohedron"), likely coated in hematite or pseudomorphed to goethite/limonite.

i think at hauerite, a manganese+sulphur mineral by checking pictures here on mindat i found very similar shape specimens.i dont know what kind of test you can do to be sure. maybe a streak test. at least the shape look more similar than all the other possibilities like pyrite . bye



Edited 1 time(s). Last edit at 08/08/2012 11:37PM by Yanick Beaudet.

It's a 12-sided dice! Like from Dungeons and Dragons, or one of those other role playing game dice sets. Roll for initiative!

Seriously though, like they said...98% probably pyrite or some altered form of pyrite. The only other mineral that forms crystals even remotely similar to this (that I know of) is cobaltite, which is much less common and probably not found in that area.