Mineral, Cu₂O; sp. gr. 5.8–6.1; hardness 3.5–4.0; cubic; red to nearly black; brownish-red streak; adamantine to sub-metallic lustre; crystals usually octahedral and acicular, but can be granular and rhombododecahedral; cleavage poor {111}; usually occurs in the oxidized zone of copper deposits, as a secondary mineral, and associated with malachite and azurite. It is a minor ore mineral for copper.