Good crystals are rare, but prized when found. Although the color is usually just a velvety black the luster is generally high and striking. Color is dark pithchy to velvety black to dark brown. Luster is vitreous to resinous and fresh surfaces can have a submetallic luster. Crystals are nearly opaque.
Cleavage is poor in one direction.
Fracture is conchoidal. Extreme variation caused by variable composition of component metals. Streak is reddish brown. Best Field Indicators are luster, fracture, color, streak, radioactivity, associations, environment and specific gravity.