Nolanite supergroup of minerals: nomenclature and classification

Abstract. The nolanite supergroup has been established and approved by the IMA CNMNC. It contains eight mineral species with the nolanite-type structure. They are hexagonal with the space group P63mc and unit-cell parameters in the following ranges: a=5.5–6.0 Å and c=8.8–10.3 Å; Z=2. The nolanite supergroup is subdivided into three groups (nolanite, kamiokite, and rinmanite groups) in accordance with the largest charge of species-defining cations, which coincides with the largest charge of octahedral M cations (+3, +4, and +5, respectively). Their general formulae are M133+M23+T3+O7(OH) (nolanite group: nolanite, V43+Fe3+O7(OH); akdalaite, Al5O7(OH); and ferrihydrite, Fe53+O7(OH)), M134+M22+T2+O8 (kamiokite group: kamiokite, Fe22+Mo34+O8; iseite, Mn22+Mo34+O8; and majindeite, Mg2Mo34+O8), and (M123+M12+)M25+T2+O7(OH) (rinmanite group: rinmanite, (Fe23+Mg)Sb5+ZnO7(OH), and zincorinmanite-(Zn), (Fe23+Zn)Sb5+ZnO7(OH)). Relationships between members of each group can be described by homovalent substitution schemes, whereas relationships between different groups are determined only by heterovalent substitution schemes. All historical names of minerals belonging to the nolanite supergroup are preserved. In new minerals of the nolanite supergroup, each combination of the M1 and M2 cations defines the root name. A Levinson-type suffix should be applied to indicate the dominant component at the tetrahedrally coordinated T site. The charge-balancing M12+ cation defines the prefix (magnesio-, zinco-, mangano-, etc.).