Common Forms/Occurrences: Common constituent of Precambrian iron-formations Useful Identification Test: Attracted to a magnet and can be magnetized Chemical formula: Fe3O4 Crystal System: Octahedrons Colour: Silvery gray to black Streak: Dark gray Lustre: Metallic (M) Cleavage: No cleavage Fracture: Subconchoidal Hardness: 6 Hardness Search: six Specific Gravity: 5.0 - 5.2