May contain many impurities partially replacing both the first and the second iron.
Crystals are usually well-shaped octahedrons , and less commonly dodecahedrons .
They may also be an interesting combination of the two. Seldom occurs in cubic crystals. Crystals are usually striated , and some octahedral crystals contain layer growths. Also occurs massive , grainy , in veins , as large embedded grains , and as rounded crystals. Transparency Opaque Specific Gravity 4.9 - 5.2 Luster Metallic Cleavage None.