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 (A2+B3+2O4) and the ulvöspinel subgroup 4-2 (A4+B2+2O4) ⁠, the thiospinel group (20 species) into the carrollite subgroup 1-3.5 (A1+B3.5+2S4) and the linnaeite subgroup 2-3 (A2+B3+2S4) ⁠, finally, the selenospinel group (3 species) into the bornhardtite subgroup 2-3 (A2+B3+2Se4) and the potential “tyrrellite subgroup” (⁠ A1+B3.5+2S4 ⁠, 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”.

Nomenclature and classification of the spinel supergroup

BIAGIONI C.;PASERO M.
2019-01-01

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 (A2+B3+2O4) and the ulvöspinel subgroup 4-2 (A4+B2+2O4) ⁠, the thiospinel group (20 species) into the carrollite subgroup 1-3.5 (A1+B3.5+2S4) and the linnaeite subgroup 2-3 (A2+B3+2S4) ⁠, finally, the selenospinel group (3 species) into the bornhardtite subgroup 2-3 (A2+B3+2Se4) and the potential “tyrrellite subgroup” (⁠ A1+B3.5+2S4 ⁠, 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”.
2019
Bosi, F.; Biagioni, C.; Pasero, M.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/939058
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