Reference work entry
Magnetite is an important iron mineral that contains Fe 3O 4. The crystal shape is octahedral or dodecahedral, and it also appears as blocky or granular aggregates. Its colour and streaks are black. It has opaque diaphaneity, a sub-metallic lustre, a specific gravity of 5.2, a Mohs hardness of 5.5–6.5, and sub-conchoidal to uneven fractures. It mainly forms in magmatic rocks and sometimes in metasomatic mineral ores and metamorphosed iron ore beds (Fig. 3).
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