Nomenclature of the garnet supergroup

Abstract

The garnet supergroup includes all minerals isostructural with garnet regardless of what elements occupy the four atomic sites, i.e., the supergroup includes several chemical classes. There are presently 32 approved species, with an additional 5 possible species needing further study to be approved. The general formula for the garnet supergroup minerals is {X 3 }[Y 2 ](Z 3)ϕ 12 , where X, Y, and Z refer to dodecahedral, octahedral, and tetrahedral sites, respectively, and ϕ is O, OH, or F. Most garnets are cubic, space group Ia3d (no. 230), but two OH-bearing species (henritermierite and holtstamite) have tetragonal symmetry, space group, I4 1 /acd (no. 142), and their X, Z, and ϕ sites are split into more symmetrically unique atomic positions. Total charge at the Z site and symmetry are criteria for distinguishing groups, whereas the dominant-constituent and dominant-valency rules are critical in identifying species. Twenty-nine species belong to one of five groups: the tetragonal henritermierite group and the isometric bitikleite, schorlomite, garnet, and berzeliite groups with a total charge at Z of 8 (silicate), 9 (oxide), 10 (silicate), 12 (silicate), and 15 (vanadate, arsenate), respectively. Three species are single representatives of potential groups in which Z is vacant or occupied by monovalent (halide, hydroxide) or divalent cations (oxide). We recommend that suffixes (other than Levinson modifiers) not be used in naming minerals in the garnet supergroup. Existing names with suffixes have been replaced with new root names where necessary: bitikleite-(SnAl) to bitikleite, bitikleite-(SnFe) to dzhuluite, bitikleite-(ZrFe) to usturite, and elbrusite-(Zr) to elbrusite. The name hibschite has been discredited in favor of grossular as Si is the dominant cation at the Z site. Twenty-one end-members have been reported as subordinate components in minerals of the garnet supergroup of which six have been reported in amounts up to 20 mol% or more, and, thus, there is potential for more species to be discovered in the garnet supergroup. The nomenclature outlined in this report has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (Voting Proposal 11-D).

Química Mineral de Granada no Estudo da Proveniência Sedimentar do Litoral Norte do Estado do Rio de Janeiro, Brasil

“…Alguns desses campos (B e C) foram subdivididos por Mange & Morton (2007) para uma maior precisão na correlação entre a composição dos grãos de granada e suas rochas-fonte (Tabela 2; ver diagramas na Figura 7). Tabela 1 Grupo da granada: principais membros finais, densidade relativa (Deer et al, 1992) e fórmula química (Grew et al 2013).…”

“…Desta forma, o trabalho propõe a análise da composição química de grãos de granada encontrados neste segmento do cordão litorâneo e a correlação com as possíveis rochas-fonte destes sedimentos. (Deer et al, 1992;Grew et al, 2013), das quais as principais estão especificadas na Tabela 1.…”

Ti–in–garnet thermometer for ultrahigh–temperature granulites

“…Chakhmouradian and McCammon (2005) concluded there is little evidence for tetrahedral Ti in Ti-rich garnet. Grew et al (2013) approved that Ti occupies the octahedral position in garnet structure and proposed the end-member formulae of Ti-garnet: Ca 3 [Ti 2 ] {SiFe 3+ 2 }O 12 for schorlomite (Ito and Frondel, 1967) and Ca 3 [TiFe 2+ ]Si 3 O 12 for morimotoite (Henmi et al, 1995). Ma and Krot (2014) found the new Ti-garnet in which Ti occupies all octahedral site (hutcheonite, Ca 3 Ti 2 SiAl 2 O 12 ) in the Allende meteorite.…”

The dumortierite supergroup. I. A new nomenclature for the dumortierite and holtite groups

“…4 (adapted from Grew et al, 2013). Members of the IMA CNMNC and two anonymous reviewers are thanked for their comments on earlier versions of this manuscript.…”