Habit: Chestnut to reddish brown or salmon pink; brownish black to black if altered. Crystals typically very rough but have many indistinct forms; usually nodular or massive. Vitreous to resinous luster; translucent to opaque. Yellowish gray streak.
Environment: A principal primary phosphate or one that has replaced earlier species.
Etymology: From the Greek for "threefold," probably for its three cleavage directions.