The systematics of the spinel-type minerals: An overview

Compounds with a spinel-type structure include mineral species with the general formula AB(2 phi 4), where phi can be O2-, S2-, or Se2-. Space group symmetry is Fd (3) over barm, even if lower symmetries are reported owing to the off-center displacement of metal ions. In oxide spinels (phi = O2-), A and B cations can be divalent and trivalent (2-3 spinels) or, more rarely, tetravalent and divalent (4-2 spinels). From a chemical point of view, oxide spinels belong to the chemical classes of oxides, germanates, and silicates. Up to now, 24 mineral species have been approved: ahrensite, brunogeierite, chromite, cochromite, coulsonite, cuprospinel, filipstadite, franklinite, gahnite, galaxite, hercynite, jacobsite, magnesiochromite, magnesiocoulsonite, magnesioferrite, magnetite, manganochromite, qandilite, ringwoodite, spinel, trevorite, ulvospinel, vuorelainenite, and zincochromite. Sulfospinels (phi = S2-) and selenospinels (phi = Se2-) are isostructural with oxide spinels. Twenty-one different mineral species have been approved so far; of them, three are selenospinels (bornhardtite, trustedtite, and tyrrellite), whereas 18 are sulfospinels: cadmoindite, carrollite, cuproiridsite, cuprokalininite, cuprorhodsite, daubreelite, ferrorhodsite, fletcherite, florensovite, greigite, indite, kalininite, linnaeite, malanite, polydymite, siegenite, violarite, and xingzhongite. The known mineral species with spinel-type structure are briefly reviewed, indicating for each of them the type locality, the origin of the name, and a few more miscellaneous data. This review aims at giving the state-of-the-art about the currently valid mineral species, considering the outstanding importance that these compounds cover in a wide range of scientific disciplines.