Color is steel or silver gray to black in some forms and red to brown in earthy forms. Sometimes tarnished with irredescent colors when in a hydrated form (called Turgite).
Luster is metallic or dull in earthy and oolitic forms.
Transparency: Crystals are opaque.
Crystal System is trigonal; bar 3 2/m
Crystal Habits include tabular crystals of varying thickness sometimes twinned, micaceous (specular), botryoidal and massive. also earthy or oolitic.
Cleavage is absent however there is a parting on two planes.
Fracture is uneven.
Hardness is 5 - 6
Specific Gravity is 5.3 (slightly above average for metallic minerals)
Streak is blood red to brownish red for earthy forms.
