Spinelle

Spinelle, or SPINEL, is a compound of the oxides of magnesium and aluminium, its composition corresponding to the formula MgAl₂O₄. It occurs naturally, crystallising in forms of the Rhombic system. The crystals may be colourless or tinted, owing to the presence of other metallic oxides which may partially replace the magnesium. By this partial replacement we may thus obtain iron spinelle, a zinc spinelle, etc., with formulae (MgFe) Al₂O₄, (MgZn) Al₂O₄, etc.