Bornite is only isometric at temperatures above 228 degrees celsius and it was above this temperature that the crystals formed. Color is brown to black with a typical purplish-bluish tarnish, a reddish bronze color on freshly broken surfaces. Luster is metallic. Crystals are opaque. Crystal Habits include rare distorted cubes and even more rarely dodecahedrons and octahedrons.
Most common habit is massive or disseminated grains.
Cleavage is very poor, octahedral. Fracture is conchoidal. Streak is a gray black. The tarnish that occurs on fresh surfaces can form in only hours and will become black over time. Associated Minerals are magnetite , chalcocite , chalcopyrite , covellite , pyrrhotite , pyrite and other sulfides .