Although most crystals are embedded and do not show good form, some crystals are exceptional and can demonstrate a high luster. Color is black with a tinge of yellow, brown or green. Luster is greasy to submetallic. Crystals are opaque. Cleavage is absent.
Fracture is conchoidal.
Extreme variation caused by variable composition of component metals. Streak is yellow, brown or gray. Best Field Indicators are luster, fracture, color, radioactivity, associations, environment and specific gravity.