spinelgroup

Spinelgroup is a family of minerals that share a common crystal structure and the general chemical formula AB2O4. In this formula, A represents a divalent cation and B represents a trivalent cation, both occupying specific sites within the crystal lattice. The most well-known member of this group is spinel itself, which has the formula MgAl2O4. Other common minerals in the spinel group include magnetite (Fe3O4), hercynite (FeAl2O4), gahnite (ZnAl2O4), and chromite (FeCr2O4). These minerals are characterized by their isometric crystal system, typically forming octahedral or dodecahedral crystals. They often exhibit high hardness, good cleavage, and a vitreous luster. The wide range of chemical compositions within the spinel group leads to a diverse array of colors, from the deep red of ruby spinel and the vibrant blue of cobalt spinel to the black of magnetite and the green of some chromites. Many spinels are prized as gemstones, with ruby and sapphire, which are varieties of corundum, sometimes being confused with red and blue spinels respectively. Spinel minerals are found in a variety of geological environments, including metamorphic rocks, igneous rocks, and as accessory minerals in meteorites. Their refractive index and specific gravity are useful properties for identification.