Nomenclature and classification of the spinel supergroup

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 AB 2 X 4 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 (TX 4) isolated from each other and sharing corners with the neighboring six-fold coordination polyhedra (MX 6), which, in turn, share six of their twelve X-X edges with nearestneighbor MX 6. 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: O 2-(oxyspinel), S 2-(thiospinel), and Se 2-(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 AB 2 X 4. The oxyspinel group (33 species) can be divided into the spinel subgroup 2-3 ðA 2þ B 3þ 2 O 4 Þ and the ulvöspinel subgroup 4-2 ðA 4þ B 2þ 2 O 4 Þ, the thiospinel group (20 species) into the carrollite subgroup 1-3.5 ðA 1þ B 3:5þ 2 S 4 Þ and the linnaeite subgroup 2-3 ðA 2þ B 3þ 2 S 4 Þ, finally, the selenospinel group (3 species) into the bornhardtite subgroup 2-3 (A 2+ B 3+ 2 Se 4) and the potential ''tyrrellite subgroup'' (A 1þ B 3:5þ 2 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''.

Mineralogical Diversity of Ca2SiO4-Bearing Combustion Metamorphic Rocks in the Hatrurim Basin: Implications for Storage and Partitioning of Elements in Oil Shale Clinkering

“…Minerals of this supergroup are among the main opaque phases in the larnite rocks. According to the recent nomenclature [125], they belong to the oxyspinel group and are classified as spinel, magnesioferrite, and magnetite ( Figure 7C (Table 21; Figure 15). Cr-rich spinel (~24 wt % Cr 2 O 3 ) and magnetite (<1.5 w t% TiO 2 ) have been found in the mayenite-bearing variety, while magnesioferrite is of rare occurrence.…”

Structural Trends and Solid-Solutions Based on the Crystal Chemistry of Two Hausmannite (Mn3O4) Samples from the Kalahari Manganese Field

“…The formal charge of A and B constituents can range from 0 to +6 [3]. In "normal" spinels, the A constituent occupies the 4-coordinated tetrahedral T site and the B constituent occupies the 6-coordinated octahedral metal M site [4]. In "inverse" spinels, the T site contains only B cations and the M site contains an equal number of A and B cations, so the M site is fully disordered.…”

“…In "inverse" spinels, the T site contains only B cations and the M site contains an equal number of A and B cations, so the M site is fully disordered. Intermediate spinels may be expressed as a mix of normal and inverse end-members, with the general formula, [4] [A 1−x B x ] [6] (A x B 2−x )O 4 , where the variable x is referred to as the "inversion parameter". This x is the fraction of B cations at the T site.…”

“…he structure of cubic spinels consists of T cations at 8a (1/8, 1/8, 1/8), M cations at 16d (½ nd O atoms on the body diagonals of a cube at 32e (u, u, u), where u is approximately group Fd⎯3m. In a cubic spinel structure, there are only two structural variables (ex cement parameters): the a unit-cell parameter and the O atom positional parameter, u. ausmannite, ideally Mn3O4, is a normal spinel with a distorted tetragonal structure (Figu ember hausmannite structural formula is [4] [Mn 2+ ] [6] (Mn2 3+ )O4. The T site may be occupie ent cations (e.g., Mn 2+ , Mg 2+ , Zn 2+ , or Fe 2+ ), and the Jahn-Teller elongated MO6 octahedron cupied by trivalent cations (e.g., Mn 3+ , Fe 3+ , or Al 3+ ).…”

“…Table 1. Unit-cell parameters and bond distances for hausmannite, [4] [T 2+ ] [6] (M 3+ ) In hausmannite, the T and M sites are at fixed positions and the O-atom coordinate is at (0, x, y). The O atom is positioned to balance between the co-Operative Jahn-Teller distortion around the Mn 3+ site, stretching of the Mn 3+ O 6 octahedron along [001], countered by the force of the tetrahedron preserving its regular form against the tetragonal deformation of the structure [16,22].…”