Characteristics: Hard white metal of the platinum group. On heating in air it gives off poisonous fume of osmium tetroxide. Insoluble in acids and aqua regia. Osmium is attacked by fused alkalies. It has the highest specific gravity and melting point of the platinum metals. It is metallurgically unworkable.
Hazard: Irritant to skin.
Derivation: Occurs with platinum from which it is recovered during the purification process. Also occurs with iridium as a natural alloy, iridosmine.