Original paper
Nomenclature and classification of the spinel supergroup
Bosi, Ferdinando; Biagioni, Cristian; Pasero, Marco
European Journal of Mineralogy Volume 31 Number 1 (2019), p. 183 - 192
77 references
published: Feb 21, 2019
published online: Sep 12, 2018
manuscript accepted: Jul 6, 2018
manuscript revision received: Jun 25, 2018
manuscript received: Apr 11, 2018
DOI: 10.1127/ejm/2019/0031-2788
Open Access (paper may be downloaded free of charge)
Abstract
A new, IMA-approved classification scheme for the spinel-supergroup minerals is here reported. To belong to the spinel supergroup, a mineral must meet two criteria: (i) the ratio of cation to anion sites must be equal to 3:4, typically represented by the general formula AB2X4 where A and B represent cations (including vacancy) and X represents anions; (ii) its structure must comprise a heteropolyhedral framework of four-fold coordination polyhedra (TX4) isolated from each other and sharing corners with the neighboring six-fold coordination polyhedra (MX6), which, in turn, share six of their twelve X-X edges with nearest-neighbor MX6. Regardless of space group, the X anions form a cubic close-packing and each X anion is bonded to three M-cations and one T-cation. The fifty-six minerals of the spinel supergroup are divided into three groups on the basis of dominant X anion: O2– (oxyspinel), S2– (thiospinel), and Se2– (selenospinel). Each group is composed of subgroups identified according to the dominant valence and then the dominant constituent (or heterovalent pair of constituents) represented by the letter B in the formula AB2X4. The oxyspinel group (33 species) can be divided into the spinel subgroup 2-3 ( A 2 + B 2 3 + O 4 ) and the ulvöspinel subgroup 4-2 ( A 4 + B 2 2 + O 4 ) , the thiospinel group (20 species) into the carrollite subgroup 1-3.5 ( A 1 + B 2 3.5 + S 4 ) and the linnaeite subgroup 2-3 ( A 2 + B 2 3 + S 4 ) , finally, the selenospinel group (3 species) into the bornhardtite subgroup 2-3 (A2+B3+ 2Se4) and the potential “tyrrellite subgroup” ( A 1 + B 2 3.5 + S 4 , currently composed by only one species). Once the subgroup is established based on the valence of B, then the mineral species is identified by the combination of the dominant A- and B-cations. Moreover, the present nomenclature redefines the ideal formulae of titanomaghemite, cuprorhodsite, malanite, maghemite, filipstadite, tegengrenite, rhodostannite, toyohaite and xingzhongite as well as discredits “iwakiite”, “hydrohetaerolite” and “ferrorhodsite”.
Keywords
spinel • oxyspinel • thiospinel • selenospinel • nomenclature • classification