Natural Spinel Crystals
Spinel crystallizes in the isometric system; The spinel structure Normal spinel structures are usually cubic close-packed oxides with eight tetrahedral and four octahedral sites per formula unit. common crystal forms are octahedra, usually twinned. It has an imperfect octahedral cleavage and a conchoidal fracture. Its hardness is 8, its specific gravity is 3.5–4.1
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