Nolanite supergroup of minerals: nomenclature and classification

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 M1${}_{\mathrm{3}}^{\mathrm{3}+}M$2${}^{\mathrm{3}+}{T}^{\mathrm{3}+}$O₇(OH) (nolanite group: nolanite, V${}_{\mathrm{4}}^{\mathrm{3}+}$Fe³⁺O₇(OH); akdalaite, Al₅O₇(OH); and ferrihydrite, Fe${}_{\mathrm{5}}^{\mathrm{3}+}$O₇(OH)), M1${}_{\mathrm{3}}^{\mathrm{4}+}M$2${}^{\mathrm{2}+}{T}^{\mathrm{2}+}$O₈ (kamiokite group: kamiokite, Fe${}_{\mathrm{2}}^{\mathrm{2}+}$Mo${}_{\mathrm{3}}^{\mathrm{4}+}$O₈; iseite, Mn${}_{\mathrm{2}}^{\mathrm{2}+}$Mo${}_{\mathrm{3}}^{\mathrm{4}+}$O₈; and majindeite, Mg₂Mo${}_{\mathrm{3}}^{\mathrm{4}+}$O₈), and (M1${}_{\mathrm{2}}^{\mathrm{3}+}M$1²⁺)M2${}^{\mathrm{5}+}{T}^{\mathrm{2}+}$O₇(OH) (rinmanite group: rinmanite, (Fe${}_{\mathrm{2}}^{\mathrm{3}+}$Mg)Sb⁵⁺ZnO₇(OH), and zincorinmanite-(Zn), (Fe${}_{\mathrm{2}}^{\mathrm{3}+}$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.).

1 Introduction

Among oxide minerals with the stoichiometry M1₃M2TO₇X (X= O, OH), there are eight mineral species with the nolanite-type structure (Fig. 1). All of them 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. Their crystal structures are composed of alternating layers of two kinds: a layer of edge-sharing M1 octahedra (O layer) and a heteropolyhedral (H) layer of M2 octahedra and T tetrahedra connected via common vertices (Fig. 2). The M1 octahedra are connected with the H layers situated above and below it via common edges with M2 octahedra and via common vertices with T tetrahedra, and, thus, a quasi-framework forms. The X site is coordinated by M1 cations. The cations occupying polyhedra of the quasi-framework are very different in their charges. These minerals are different not only in bulk chemical composition but also in the distribution of cations over tetrahedral and octahedral sites (see Table 1 and references below). Nolanite, described in 1957 (Robinson et al., 1957), was the first mineral species belonging to this structure type.

Table 1 Comparative data of nolanite-supergroup minerals with the general formula M1₃M2TO₇X (X= O, OH).

Note: powder X-ray diffraction data for akdalaite and ferrihydrite published by Shpanov et al. (1971) and Chukhrov et al. (1973), respectively, may correspond to polluted samples. More reliable d values for the strongest lines of akdalaite (without data on their intensities) given by Hwang et al. (2006) are 4.84, 4.42, 4.23, 2.78, 2.53, 2.36, 1.67, 1.44, and 1.42 Å.

Figure 1 The crystal structure of a nolanite-supergroup mineral: general view. The unit cell is outlined.

Figure 2 Layer of octahedra (O layer) (a) and heteropolyhedral (H) layer (b) in the nolanite-type structure. The unit cell is outlined. For the legend, see Fig. 1.

The mineral species with the nolanite-type structure were united to a mineral supergroup named the nolanite supergroup. The nomenclature and classification of the nolanite supergroup presented in this paper were approved by the IMA Commission on New Minerals, Nomenclature and Classification in 2024 (Memorandum 127-SM24).

2 Minerals belonging to the nolanite supergroup

The guidelines for the identification of three groups within the nolanite supergroup are (1) the highest charge q₁ of the chemical constituents at the octahedral M(1) and M(2) sites and (2) the dominant species at the X site (X= O or OH). In accordance with these criteria, the nolanite supergroup can be subdivided into three groups: nolanite group with $q_{\mathrm{1}}=+\mathrm{3}$ (for both M1 and M2) and X= OH, kamiokite group with $q_{\mathrm{1}}=+\mathrm{4}$ (for M1) and X= O, and rinmanite group with $q_{\mathrm{1}}=+\mathrm{5}$ (for M2) and X= OH. The general formulae of minerals belonging to these groups are M1${}_{\mathrm{3}}^{\mathrm{3}+}M$2${}^{\mathrm{3}+}{T}^{\mathrm{3}+}$O₇(OH), M1${}_{\mathrm{3}}^{\mathrm{4}+}M$2${}^{\mathrm{2}+}{T}^{\mathrm{2}+}$O₈, and (M1${}_{\mathrm{2}}^{\mathrm{3}+}M$1²⁺)M2${}^{\mathrm{5}+}{T}^{\mathrm{2}+}$O₇(OH), respectively.

In this approach, octahedral positions are considered together. An additional criterion for the mineral group definition is the charge q₂ of a cation in the tetrahedral T site: $q_{\mathrm{2}}=+\mathrm{3}$ for the nolanite-group minerals and $q_{\mathrm{2}}=+\mathrm{2}$ for minerals belonging to the kamiokite and rinmanite groups. This classification makes it possible to calculate crystal-chemical formulae of nolanite-supergroup minerals based on chemical data only (see below).

If compositions with $q_{\mathrm{1}}=+\mathrm{4}$ and OH at X were to be found, that would constitute a new group. The general crystal-chemical formulae of the members of this group would be M1${}_{\mathrm{3}}^{\mathrm{3}+}M$2${}^{\mathrm{4}+}{T}^{\mathrm{2}+}$O₇(OH) or (M1${}_{\mathrm{2}}^{\mathrm{3}+}M$1²⁺)M2${}^{\mathrm{4}+}{T}^{\mathrm{3}+}$O₇(OH) (the formula M1${}_{\mathrm{3}}^{\mathrm{3}+}M$2${}^{\mathrm{4}+}{T}^{\mathrm{3}+}$O₇O is not allowed because the occurrence of R³⁺ at M1 site does not allow for such charge compensation at the X site).

Since the octahedral sites are considered together, minerals with the crystal chemical formulae (M1${}_{\mathrm{2}}^{\mathrm{4}+}M$1²⁺)M2${}^{\mathrm{4}+}{T}^{\mathrm{2}+}$O₇O and M1${}_{\mathrm{3}}^{\mathrm{4}+}M$2${}^{\mathrm{2}+}{T}^{\mathrm{2}+}$O₇O are members of the same group (namely, kamiokite group) with the general formula $R_{\mathrm{2}}^{\mathrm{2}+}$R${}_{\mathrm{3}}^{\mathrm{4}+}$O₈. This approach eliminates ambiguity in determining mineral species based on chemical composition data in the absence of structural data.

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.

3 Nolanite group

The nolanite group unites minerals containing only trivalent species-defining cations ($q_{\mathrm{1}}=+\mathrm{3}$). Their generalized crystal-chemical formula is M1${}_{\mathrm{3}}^{\mathrm{3}+}M$2${}^{\mathrm{3}+}{T}^{\mathrm{3}+}$O₇(OH).

Nolanite, V${}_{\mathrm{4}}^{\mathrm{3}+}$Fe³⁺O₇(OH) = V${}_{\mathrm{3}}^{\mathrm{3}+}$V³⁺Fe³⁺O₇(OH), has been discovered in a hydrothermal uranium deposit on the shore of Fish Hook Bay, Lake Athabasca, in the Beaverlodge region of Saskatchewan, Canada (Robinson et al., 1957). Thereafter, this mineral was found in gold deposits hosted by metamorphosed greenstones in Kalgoorlie, Western Australia (Taylor and Radtke, 1967; Gatehouse et al., 1983); in the Yushui Cu deposit, the province of Guangdong, South China (Liu et al., 2023); and in the Vihanti metamorphosed volcanic-hosted massive sulfide Zn deposit situated in the North Ostrobothnia region, Finland (Voloshin et al., 2014). Based on wet chemical analyses, it was initially supposed that nolanite contains significant amounts of Fe²⁺ and V⁴⁺ (along with V³⁺) and does not contain hydrogen (Robinson et al., 1957).

In the first model of the crystal structure of a sample from the type locality (Hanson, 1958), the site occupancies were not refined, and nolanite was tentatively considered a V⁴⁺-dominant mineral with the formula Fe${}_{\mathrm{2.5}}^{\mathrm{2}+}$V${}_{\mathrm{1.5}}^{\mathrm{3}+}$V${}_{\mathrm{6}}^{\mathrm{4}+}$. However, subsequent chemical analyses and the refinement of the crystal structure of nolanite samples from Kalgoorlie showed that in this mineral, the tetrahedrally coordinated T site contains mainly Fe³⁺ (with subordinate Fe²⁺), and the M1 and M2 octahedra are occupied by V³⁺ with subordinate Ti and minor Al and/or Fe²⁺ (Gatehouse et al., 1983). The generalized crystal-chemical formula of nolanite from Kalgoorlie is M¹(V³⁺,Ti,Al,Fe²⁺)₃M²(V${}^{\mathrm{3}+},$Ti,Al,Fe²⁺)^T(Fe³⁺,Fe²⁺) O₇(OH). The total content of minor cations (Ti, Fe²⁺) involved in heterovalent substitutions in the studied samples is 0.3–0.55 atoms per formula unit (apfu) (Z=2).

Akdalaite, Al₅O₇(OH) = Al₃AlAlO₇(OH), has been discovered as imperfect elongate-tabular crystals up to 0.1×0.8 mm in veinlets composed of muscovite and fluorite at the Solnechnoe fluorite deposit, Karaganda Region, Kazakhstan (Shpanov et al., 1971). The bulk empirical formula of the holotype sample is (Al_4.74Be_0.09Mg_0.07Fe${}_{\mathrm{0.04}}^{\mathrm{3}+}$Zn_0.03)_Σ4.97[O_6.73(OH)_1.21F_0.06]_Σ8.00, which is similar to the formulae of some members of the högbomite supergroup whose crystal structures contain a nolanite-type module. Regarding its physical, chemical, and powder X-ray diffraction characteristics, akdalaite is similar to the synthetic aluminum hydroxide, tohdite 5Al₂O₃•H₂O, hexagonal, with a=5.575(1) Å and c=8.761(1) Å (Yamaguchi et al., 1964, 1969). However, in the first description of akdalaite (Shpanov et al., 1971) different unit-cell parameters are given: a=12.87 Å and c=14.97 Å. Subsequent studies have shown that these parameters are incorrect.

The crystal structure of tohdite has been refined using powder X-ray diffraction data with the Rietveld method (Yamaguchi et al., 1969). In this structure four-fifths of the aluminum atoms are in octahedral sites, and the rest are in tetrahedral sites. The refinement of the crystal structure of nolanite (Gatehouse et al., 1983) has confirmed that this mineral and tohdite, the synthetic akdalaite analogue, are isostructural.

Electron diffraction data for the akdalaite sample from the Kulet Kol region, Kokchetav Massif, northern Kazakhstan, yielded the unit-cell parameters a=5.58(1) Å and c=8.86(2) Å, space group P6₃mc (Hwang et al., 2006). The akdalaite-type specimen, re-examined by Hwang et al. (2006), has similar unit-cell parameters: a=5.59(1) Å and c=8.82(1) Å. Electron microprobe analyses of the sample from the Kokchetav Massif show minor Si, Ti, Cr, Fe, Mg, Zn, and Ga admixtures, in addition to the major component, Al.

Akdalaite has been also identified as a component of bauxite from Weipa, Cook Shire, Queensland, Australia (Tilley and Eggleton, 1996), and as a product of the eruption of the Bulla mud volcano, Bulla Island, Baku Archipelago, near the city of Baku, Azerbaijan (Novgorodova and Mamedov, 1996).

Ferrihydrite, Fe${}_{\mathrm{5}}^{\mathrm{3}+}$O₇(OH) = Fe${}_{\mathrm{3}}^{\mathrm{3}+}$Fe³⁺Fe³⁺O₇(OH), is widespread in the soils and different weathered rocks. The cotype localities of ferrihydrite are Leninogorskoe (formerly Ridder) and Belousovskoe Pb–Zn deposits, both situated in northeastern Kazakhstan (Chukhrov et al., 1973). Natural material is insufficiently characterized because it often forms fine mixtures with other minerals and does not form perfect crystals suitable for single-crystal X-ray structure analysis. Ferrihydrite is a nanosized mineral with a long history of debate on its crystal structure, composition, and formation mechanisms (Boily and Song, 2020, and references therein). The first structure models have been obtained for the synthetic ferrihydrite analogue. Manceau and Drits (1993) and Drits et al. (1993) (see also references therein) discussed in detail several suggested models of ferrihydrite (Towe and Bradley, 1967; Harrison et al., 1967; Eggleton and Fitzpatrick, 1988) and supposed that the studied ferrihydrite samples are mixtures of a defect-free phase with the space group P-31c and unit-cell parameters a=2.96 and c=9.40 Å, defective ferrihydrite with the hexagonal supercell with a=5.126 Å, and ultradispersed hematite with the mean dimension of coherent scattering domains of 10–20 Å. The crystal structure of the synthetic ferrihydrite analogue has been refined by modeling of the pair distribution function derived from direct Fourier transformation of the X-ray scattering data (Michel et al., 2007, 2010). The model is consistent with the nolanite-type structure with 20 % tetrahedrally and 80 % octahedrally coordinated iron, space group P6₃mc. It was also shown that short- and intermediate-range ordering of the naturally occurring ferrihydrite – characterized by high-energy X-ray scattering, pair distribution function analysis, and transmission electron microscopy – is comparable to the synthetic ferrihydrite analogue (Cismasu et al., 2011). Manceau et al. (2014) proposed for ferrihydrite a modified akdalaite structure model in which Fe has only octahedral coordination. Later it was shown that the single-phase model of Michel et al. (2007) matches the experimental data without the need for multi-phase structures (Chappell et al., 2017, and references therein; Sassi and Rosso, 2019). Funnell et al. (2020) evaluated the two principal contending models (a multi-phase system without tetrahedrally coordinated iron and the single-phase model with tetrahedrally coordinated iron) and stated that the multi-phase model requires unphysical structural rearrangements to fit the data, whereas the single-phase one accounts for the data straightforwardly. Thus, the latter provides the more accurate description of the short- and intermediate-range order of ferrihydrite (Funnell et al., 2020).

Ferrihydrite forms an incomplete solid-solution series with akdalaite. With increasing Al and Si contents, a decrease in particle size and an increase in structural disorder were observed (Cismasu et al., 2011).

4 Kamiokite group

Minerals belonging to the kamiokite group have the generalized crystal-chemical formula M1${}_{\mathrm{3}}^{\mathrm{4}+}M$2${}^{\mathrm{2}+}{T}^{\mathrm{2}+}$O₈. Currently, only members of this group with Mo⁴⁺ at the M1 site are known.

Kamiokite, Fe${}_{\mathrm{2}}^{\mathrm{2}+}$Mo${}_{\mathrm{3}}^{\mathrm{4}+}$O₈ = Mo${}_{\mathrm{3}}^{\mathrm{4}+}$Fe²⁺Fe²⁺O₇O, has been described as a new mineral from the Kamioka mine, Japan (Sasaki et al., 1985). The mineral occurs in quartz-molybdenite stockwork veins associated with granite porphyry dikes. The empirical formula of the holotype sample is Fe${}_{\mathrm{2.01}}^{\mathrm{2}+}$Mn${}_{\mathrm{0.03}}^{\mathrm{2}+}$Mo${}_{\mathrm{2.98}}^{\mathrm{4}+}$O₈. According to the results of the crystal structure refinement of a sample from the type locality (Kanazawa and Sasaki, 1986), all Mo⁴⁺ in kamiokite occurs at the M1 site. Half of the Fe atoms are in tetrahedral coordination, at the T site, while the other half are in octahedral coordination, at the M2 site.

Another occurrence of kamiokite is the Mohawk mine, Michigan, USA, where this mineral occurs in fissure veins filled during low-grade regional metamorphism of basalt. The empirical formula of kamiokite from the Mohawk mine derived based on electron microprobe analyses and structural considerations is (Fe${}_{\mathrm{1.54}}^{\mathrm{2}+}$Cu_0.16Fe${}_{\mathrm{0.15}}^{\mathrm{3}+}$Si_0.08Al_0.04Zn_0.03)_Σ2.00(Mo_2.52Fe${}_{\mathrm{0.15}}^{\mathrm{3}+}$ V_0.14Fe${}_{\mathrm{0.08}}^{\mathrm{2}+}$Ti_0.07Al_0.04)_Σ3.00O₈ (Johan and Picot, 1986). This formula is charge-balanced under the assumption that vanadium is tetravalent. Taking into account the scheme for assigning ionic species based on the chemical formula (see Appendix A below), this formula should be rewritten as follows:

$$\begin{array}{rl}& M^{\mathrm{1}}\left({\mathrm{Mo}}_{\mathrm{2.52}}^{\mathrm{4}+}{\mathrm{V}}_{\mathrm{0.14}}^{\mathrm{4}+}{\mathrm{Ti}}_{\mathrm{0.07}}{\mathrm{Fe}}_{\mathrm{0.27}}^{\mathrm{3}+}{)}_{\mathrm{\Sigma }\mathrm{3}}{M}^{\mathrm{2}}\right({\mathrm{Fe}}_{\mathrm{0.73}}^{\mathrm{2}+}{\mathrm{Cu}}_{\mathrm{0.16}}^{\mathrm{2}+}{\mathrm{Al}}_{\mathrm{0.08}}\\ & {\mathrm{Fe}}_{\mathrm{0.03}}^{\mathrm{3}+}{)}_{\mathrm{\Sigma }\mathrm{1}}^T({\mathrm{Fe}}_{\mathrm{0.89}}^{\mathrm{2}+}{\mathrm{Si}}_{\mathrm{0.08}}{\mathrm{Zn}}_{\mathrm{0.03}}{)}_{\mathrm{\Sigma }\mathrm{1}}{\mathrm{O}}_{\mathrm{8}}.\end{array}$$

In this formula, Si is placed at the T site with tetrahedral coordination. However, the presence of Si in the nolanite-type structure is questionable, taking into account that the ionic radius of ^[4]Si⁴⁺ (0.259 Å) is much smaller than those of bivalent cations (e.g., 0.619 Å for ^[4]Fe²⁺, 0.586 Å ^[4]Fe²⁺) (Hawthorne and Gagné, 2024). The presence of ^[4]Mo⁶⁺ or ^[6]Mo⁶⁺ (with the ionic radii of 0.398 and 0.607 Å, respectively) in the nolanite structure is also unlikely either from the point of view of local charge balance or for steric reasons.

Mg-bearing kamiokite was found in magnetite-bearing assemblages of the Allende meteorite (Ma and Beckett, 2016).

Iseite, Mn${}_{\mathrm{2}}^{\mathrm{2}+}$Mo${}_{\mathrm{3}}^{\mathrm{4}+}$O₈ = Mo${}_{\mathrm{3}}^{\mathrm{4}+}$Mn²⁺Mn²⁺O₇O, has been discovered in rhodochrosite veins cross-cutting the Fe–Mn ore of the Shobu deposit, Shima Peninsula, Japan (Nishio-Hamane et al., 2013). The mineral forms minute (up to 20 µm across) lamellar crystals. The powder X-ray diffraction pattern of iseite is close to that of kamiokite. The Rietveld refinement of the crystal structure confirmed the presence of two Mn sites, tetrahedrally and octahedrally coordinated. The empirical formula of the studied sample is Mn_1.787Fe_0.193Mo_3.010O₈. Contents of other elements such as Ca, Mg, Ti, and W are below the detection limits.

Majindeite, Mg₂Mo${}_{\mathrm{3}}^{\mathrm{4}+}$O₈ = Mo${}_{\mathrm{3}}^{\mathrm{4}+}$MgMgO₇O, occurs as minute crystals (up to 1 µm across) in the Allende meteorite, which is classified as a CV3 carbonaceous chondrite (Ma and Beckett, 2016). The empirical formula of the studied sample is (Mg_1.57Fe_0.43)Mo_3.00O₈. Using data from electron backscatter diffraction, it was shown that majindeite has the P6₃mc symmetry and is isostructural with kamiokite and iseite. Majindeite is a natural analogue of the synthetic compound Mg₂Mo₃O₈ with the nolanite-type structure (Knorr and Mueller, 1995).

5 Rinmanite group

The generalized crystal-chemical formula of minerals belonging to the rinmanite group is (M1${}_{\mathrm{2}}^{\mathrm{3}+}M$1²⁺)M2${}^{\mathrm{5}+}{T}^{\mathrm{2}+}$O₇(OH). Currently, two members of this group are known.

Rinmanite, (Fe${}_{\mathrm{2}}^{\mathrm{3}+}$Mg)Sb⁵⁺ZnO₇(OH), has been discovered in a skarn assemblage of the Garpenberg Norra Zn–Pb mine, Hedemora, Dalarna, Sweden. Its first description and crystal structure data were reported by Holtstam et al. (2001). The empirical formula of the holotype rinmanite sample written taking into account structural data and the Mössbauer spectrum showing Fe³⁺ as the only valence state of iron (Holtstam et al., 2001) is (Zn_1.58Mn_0.31Mg_0.06)_Σ1.95Sb_2.03[(Fe${}_{\mathrm{3.88}}^{\mathrm{3}+}$Al_0.15)Mg_1.95)]_Σ5.98 O_14.01(OH)_1.99 (Z=1). The H₂O content in this sample was not determined. Recalculation of the sum of 10 M cations taking into account structural data results in the charge-balanced formula M¹[(Fe${}_{\mathrm{3.91}}^{\mathrm{3}+}$Al_0.15)Mg_1.95Sb_0.04)]_Σ6.00M²Sb${}_{\mathrm{2}}^T$(Zn_1.59Mn_0.31 Mg${}_{\mathrm{0.10}}{)}_{\mathrm{\Sigma }\mathrm{2.00}}^{{\mathrm{O}}_{\mathrm{2}}-{\mathrm{O}}_{\mathrm{4}}}$O${}_{\mathrm{14}}^{{\mathrm{O}}_{\mathrm{1}}}$[(OH)_1.75O_0.25]_Σ2.00 (according to crystal-chemical criteria, excessive Sb was placed at the octahedrally coordinated Fe³⁺-dominant M1 site). Both empirical formulae lead to the ideal end-member formula (Fe${}_{\mathrm{4}}^{\mathrm{3}+}$Mg₂)Sb₂Zn₂O₁₄(OH)₂ (Z=1), in accordance with the accepted rules of chemical identification and classification of minerals (Bosi et al., 2019a, b). In this formula, Mg²⁺ is the main charge-balancing bivalent cation at the M1 site.

In the recently discovered mineral species approved with the name zincorinmanite-(Zn), zinc is the predominant bivalent component at the M1 site. The crystal-chemical formula of the holotype sample of zincorinmanite-(Zn) is M¹[(Fe${}_{\mathrm{4.23}}^{\mathrm{3}+}$Al_0.36)(Zn_0.63Mg_0.33Fe${}_{\mathrm{0.27}}^{\mathrm{2}+}$Mn${}_{\mathrm{0.06}}^{\mathrm{2}+})$Ti_0.12] M²(Sb_1.94Ti_0.06)^TZn${}_{\mathrm{2}}^{{\mathrm{O}}_{\mathrm{2}}-{\mathrm{O}}_{\mathrm{4}}}$O${}_{\mathrm{14}}^{{\mathrm{O}}_{\mathrm{1}}}$[(OH)_1.23O_0.77] (Z=1), and the ideal end-member formula is (Fe${}_{\mathrm{2}}^{\mathrm{3}+}$Mg)SbZnO₇(OH) (Z=2) (IMA proposal 2023-107). Despite the fact that the name rinmanite-(Zn) was recently approved, it has been changed to zincorinmanite-(Zn), in accordance with recommendations of some IMA CNMNC members. This mineral originates from a metasomatic sulfide-free ore occurrence with chalcophile elements (Zn, Cu, Sb, Pd, As) located near the village of Nežilovo, Pelagonian Massif, Republic of North Macedonia (Chukanov et al., 2015).

6 Mineral names

All historical mineral names have been preserved. Historical names cannot be changed in order to standardize the nomenclature of a group or supergroup, since mixed nomenclature systems are now accepted by the IMA CNMNC (Hatert et al., 2013).

In new minerals of the nolanite supergroup, each combination of dominant octahedrally coordinated M1 and M2 cations and X anion defines the root name. The subordinate criterion is the dominant charge at the tetrahedral T site. A Levinson-type suffix should be applied to indicate the dominant component at the T site. The same principle of the application of the Levinson suffix should be applied to new members of other groups belonging to the nolanite supergroup.

The charge-balanced general crystal-chemical formula of rinmanite-group minerals, (M1${}_{\mathrm{2}}^{\mathrm{3}+}M$1²⁺)M2${}^{\mathrm{5}+}{T}^{\mathrm{2}+}$O₇(OH), can be written only with two cations at the M1 site. Currently, for charge-balancing cations, prefixes rather than Levinson-type suffixes are used (e.g., in ferricoronadite, ferrihollandite, and magnesiohögbomite). Thus, in the names of rinmanite-group minerals, the charge-balancing M1²⁺ cation defines the prefix.

Taking into account these rules and recommendations, the following names for new rinmanite-group minerals could be proposed.

6.1 Nolanite group

• The potential new mineral V${}_{\mathrm{3}}^{\mathrm{3}+}$V³⁺AlO₇(OH) should have the name nolanite-(Al).

• The potential new mineral Fe${}_{\mathrm{3}}^{\mathrm{3}+}$Fe³⁺AlO₇(OH) should have the name ferrihydrite-(Al).

• The potential new mineral V${}_{\mathrm{3}}^{\mathrm{3}+}$Fe³⁺AlO₇(OH) should have the name “new root name”-(Al).

• The potential new mineral V${}_{\mathrm{3}}^{\mathrm{3}+}$Fe³⁺Fe³⁺O₇(OH) should have the name “new root name”-(Fe³⁺).

6.2 Kamiokite group

• The potential new mineral Mo${}_{\mathrm{3}}^{\mathrm{4}+}$Fe²⁺ZnO₈ should have the name kamiokite-(Zn).

• The potential new mineral Mo${}_{\mathrm{3}}^{\mathrm{4}+}$Fe²⁺MgO₈ should have the name kamiokite-(Mg).

• The potential new mineral Mo${}_{\mathrm{3}}^{\mathrm{4}+}$Mn²⁺ZnO₈ should have the name iseite-(Zn).

• The potential new mineral Mo${}_{\mathrm{3}}^{\mathrm{4}+}$MgZnO₈ should have the name majindeite-(Zn).

• The potential new mineral Ti${}_{\mathrm{3}}^{\mathrm{4}+}$MgZnO₈ should have the name “new root name”-(Zn).

6.3 Rinmanite group

• The potential new mineral (Fe${}_{\mathrm{2}}^{\mathrm{3}+}$Fe²⁺)Sb⁵⁺ZnO₇(OH) should have the name ferrorinmanite-(Zn).

• The potential new mineral (Fe${}_{\mathrm{2}}^{\mathrm{3}+}$Mg)Sb⁵⁺MgO₇(OH) should have the name magnesiorinmanite-(Mg).

• The potential new mineral (Fe${}_{\mathrm{2}}^{\mathrm{3}+}$Mg)Sb⁵⁺Mn²⁺O₇(OH) should have the name magnesiorinmanite-(Mn²⁺).

• The potential new mineral (Al₂Mg)Sb⁵⁺MgO₇(OH) should have the name “new root name”-(Mg).

• The potential new mineral (Fe${}_{\mathrm{2}}^{\mathrm{3}+}$Mg)NbMgO₇(OH) should have the name “new root name”-(Mg).

If a composition with R⁴⁺ at M2 were to be found, that would constitute a new group with X= OH. The general formula of a member of this group would be M1${}_{\mathrm{3}}^{\mathrm{3}+}M$2${}^{\mathrm{4}+}{T}^{\mathrm{2}+}$O₇(OH) or (M1${}_{\mathrm{2}}^{\mathrm{3}+}M$1²⁺)M2${}^{\mathrm{4}+}{T}^{\mathrm{3}+}$O₇(OH). In a member of this group, the Levinson-type suffix should be applied to indicate the dominant T²⁺ or T³⁺ cation.

For potential new analogues of the known members of the nolanite and rinmanite groups with F instead of OH, the prefix “fluor” should be added. For example, the hypothetic mineral (Fe${}_{\mathrm{2}}^{\mathrm{3}+}$Zn)Sb⁵⁺ZnO₇F should be named fluorzincorinmanite-(Zn); the mineral V${}_{\mathrm{3}}^{\mathrm{3}+}$V³⁺Fe³⁺O₇F should be named fluornolanite.

7 Conclusions

The nolanite supergroup is established. It is divided into the nolanite group, the kamiokite group, and the rinmanite group, in accordance with the highest charge of the species-defining cations and the dominant X species (X= O or OH) (Table 1).

The general crystal-chemical formulae of minerals belonging to the nolanite and rinmanite groups are M1${}_{\mathrm{3}}^{\mathrm{3}+}M$2${}^{\mathrm{3}+}{T}^{\mathrm{3}+}$O₇(OH) and (M1${}_{\mathrm{2}}^{\mathrm{3}+}M$1²⁺)M2${}^{\mathrm{5}+}{T}^{\mathrm{2}+}$O₇(OH), respectively.

Minerals with the crystal chemical formulae (M1${}_{\mathrm{2}}^{\mathrm{4}+}M$1²⁺)M2${}^{\mathrm{4}+}{T}^{\mathrm{2}+}$O₇O and M1${}_{\mathrm{3}}^{\mathrm{4}+}M$2${}^{\mathrm{2}+}{T}^{\mathrm{2}+}$O₇O are considered members of the kamiokite group.

Potential new nolanite-supergroup minerals with the general formula M1${}_{\mathrm{3}}^{\mathrm{3}+}M$2${}^{\mathrm{4}+}{T}^{\mathrm{2}+}$O₇(OH) or (M1${}_{\mathrm{2}}^{\mathrm{3}+}M$1²⁺)M2${}^{\mathrm{4}+}{T}^{\mathrm{3}+}$O₇(OH) would constitute a particular group.

Each combination of the M1 and M2 cations and X anion defines the root name. In the names of new minerals, the Levinson-type suffix should be applied to indicate the dominant component at the T site, whereas the charge-balancing M1²⁺ cation in rinmanite-group minerals defines the prefix.

The rinmanite-group mineral approved recently with the name rinmanite-(Zn) is renamed zincorinmanite-(Zn). All other (historical) names have been preserved.

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.

Appendix A: Assignment of ionic species to the key sites based on chemical data

Among the species-defining cations in the known nolanite-supergroup minerals, only Fe has a variable valence state. Even in rinmanite and zincorinmanite-(Zn), which crystallized under extremely oxidizing conditions, Mn is bivalent despite the fact that the Fe³⁺ : (Fe${}^{\mathrm{3}+}+$Fe²⁺) ratio is close to 1. Therefore, in order to calculate formulae of Fe-bearing members of this group in the absence of structural data, the Fe²⁺ : Fe³⁺ ratio should be determined either by direct methods (e.g., using wet chemical analysis, Mössbauer spectroscopy, from the ratio of the intensities of the FeKβ₅ and FeKβ₁ lines in the X-ray spectrum) or calculated from the charge balance in the empirical formula. In the latter case, direct determination of H₂O is very desirable.

The recommended guidelines of the formula calculation are as follows.

• 1.

  First, tetrahedral T cations are considered. Their charges are +2 or +3.

  • 1.1.

    In nolanite-group minerals (i.e., minerals with $q_{\mathrm{1}}=+\mathrm{3}$), X= OH, and all species-defining cations (including T) are trivalent. Among them, Al shows the most pronounced affinity to the tetrahedral coordination. The occurrence of Fe³⁺ in tetrahedral coordination is also common. For other possible trivalent cations (e.g., Mn³⁺, Cr³⁺, V³⁺), the tetrahedral coordination is unusual. Therefore, if in a nolanite-group mineral the Al content is >1 atom per formula unit (apfu), one Al cation is placed in T, and the Al is placed in the octahedral sites. If Al <1 apfu, all Al is placed in T. Thereafter, T is completed first by Fe³⁺ and then (if the content of Fe³⁺ is insufficient) by admixed bivalent cations in the sequence Zn, Mg, Fe, and Mn (see item 1.2 below). The larger M1 octahedron is then filled with the remaining cations in decreasing order of their ionic radii in octahedral coordination [r(Mn³⁺) >r(Fe³⁺) >r(V³⁺) >r(Cr³⁺) >r(Al³⁺)] (Hawthorne and Gagné, 2024), and the rest of the cations are placed in M2.

  • 1.2.

    In minerals belonging to the kamiokite and rinmanite groups (i.e., minerals with $q_{\mathrm{1}}=+\mathrm{4}$ and +5, respectively), dominant T cations are bivalent. As the example of rinmanite shows, Zn has a stronger affinity for tetrahedral coordination than Mg: in this mineral all zinc is at the T site, while most magnesium occurs at the M1 site. Therefore, the filling of T must occur in the following order. First, Zn²⁺, whose radius in tetrahedral coordination is 0.586 Å (Hawthorne and Gagné, 2024), is placed in T. If there is not enough zinc, then this site is filled with divalent cations with radii closest to the radius of ^[4]Zn²⁺ in the order Mg²⁺ (r=0.573 Å), Fe²⁺ (r=0.619 Å), and Mn²⁺ (r=0.680 Å).

• 2.

  In the second step, octahedral sites of minerals belonging to the kamiokite and rinmanite groups are considered.

  • 2.1.

    If $q_{\mathrm{1}}=+\mathrm{4}$ and X= O, the nolanite-supergroup mineral is assigned to the kamiokite group. In this case, the Mo⁴⁺ cation with r=0.637 Å is placed in M1, and then M1 is completed with other tetravalent cations (in the order Ti⁴⁺ (r=0.605 Å), Sn⁴⁺ (r=0.699 Å), Zr⁴⁺ (r=0.702 Å)) and then trivalent cations whose ionic radii are the closest to the ionic radius of the dominant tetravalent cation. The rest of the cations are placed in M2.

  • 2.2.

    If $q_{\mathrm{1}}=+\mathrm{5}$ and X= OH, a nolanite-supergroup mineral is assigned to the rinmanite group. In this case, the Sb⁵⁺ cation with r=0.611 Å is placed in M2, and then M2 is completed with other pentavalent cations (in the order Nb⁵⁺ (r=0.627 Å), Ta⁵⁺ (r=0.622 Å), Bi⁵⁺ (r=0.744 Å)) and then tetravalent cations whose ionic radii are the closest to the ionic radius of the dominant pentavalent cation. The rest of the cations are placed in M1.

Appendix B: Minerals and synthetic compounds related to the nolanite supergroup

Synthetic compounds with the nolanite-type structure are characterized by a wide variety of cations (Ansell and Katz, 1966; Yamaguchi et al., 1969; Torardi and McCarley, 1985; Cheetham et al., 1989; Knorr and Mueller, 1995; Michel et al., 2007, 2010; Abe et al., 2010; Zhang et al., 2011; Playford et al., 2013; Morey et al., 2019; Parise et al., 2019; Cook et al., 2020; Prodan et al., 2022; Hao et al., 2023, and references therein).

Heteropolyhedral nolanite-like layers formed by octahedra and tetrahedra were reported for the crystal structures of swedenborgite, NaBe₄SbO₇ (Huminicki and Hawthorne, 2001, and references therein), and related synthetic compounds. It is noteworthy that these compounds are characterized by the same space group P6₃mc as nolanite-supergroup minerals and close values of unit-cell parameters. Unlike nolanite-supergroup minerals, in swedenborgite with a=5.4317(2) and c=8.8571(4) Å, heteropolyhedral layers consisting of SbO₆ octahedra and BeO₄ tetrahedra, sharing common vertices, alternate with the layers of BeO₄ tetrahedra. Na⁺ cations occupy additional sites between the layers (Huminicki and Hawthorne, 2001). Thus, we consider swedenborgite as a mineral related to the nolanite supergroup.

Nolanite-type modules, TM₄O₇(OH), alternating with spinel-type modules, T₂M₄O₈, where T and M represent tetrahedrally and octahedrally coordinated cations, respectively, occur in the structures of högbomite-supergroup minerals (Hejny and Armbruster, 2002; Armbruster, 2002; Chukanov et al., 2018; Cámara et al., 2018). These minerals belong to the polysomatic series formed by different stacking sequences of the nolanite-type and spinel-type modules. In högbomite-supergroup minerals, charge-balancing cations in the end-member formulae are considered species-defining components. A similar approach has been applied to the rinmanite group within the nolanite supergroup.