Aspects of the bond topology and chemical composition of a mineral may be incorporated into a general formula by writing the local topological details of each cation and anion, along with their chemical identity, as a general expression called a structure-generating function. Here, this procedure is described for polysomatic T–O–T and H–O–H structures. We may write tetrahedrally coordinated cations and their associated anions as {T2nΘm}. For {T2nΘm} to be a chain or ribbon, 5n < m ≤ 6n, and we may write m as 5n + N, where N is an integer. Within the {T2nΘ(5n+N)} unit, we may recognize three types of anion vertices: (1) bridging anions, Θbr, that are bonded to two T cations; (2) apical anions, Θap, that are involved in linkage to other cations out of the plane of the bridging anions; and (3) linking anions, Θl, that link to non-T cations in the plane of the bridging anions. We may incorporate the connectivity of the cations in our algebraic representation of the chain as follows: {T2nΘbraΘapbΘlc} where a + b + c = 5n + N. The apical anions of the T- or H-sheets provide some anions of the layer of octahedra. We may use the handshaking di-lemma of graph theory to examine the interaction between the two types of layers, and write a Structure-Generating Function, S(N;n), that gives both the stoichiometry and aspects of the bond topology of the structures.

Where N = 1, the T-sheet consists of ribbons of the form {T2nΘ(5n+1)} = {T2nΘbr(3n–1)Θap2nΘl2}. Each T–Θbr–T linkage spans an octahedron, and hence there are (3n – 1) octahedrally coordinated cations between opposing {T2nΘbr(3n–1)Θap2nΘl2} ribbons. There are an additional (n–1) vertices, Ψ, required to complete the coordination of the M cations on one side of the O-sheet, and we may write the structure-generating function for biopyriboles as follows: S(1;n) = Xi[M(3n–1)Ψ2(n–1){T2nΘbr(3n–1)Θap2nΘl2}2] = [M(3n–1)Ψ2(n–1){T2nΘ(5n+1)}2]. Where N = 2, the general form of the T-ribbon is {T2nΘ(5n+2)}, a component of the H-sheet in the polysomatic H–O–H minerals in which the T-ribbons are linked laterally by [5]- or [6]-coordinated high-valence cations, D, which have the coordination (Dφ41φapφt), where ft may or may not be present depending on the coordination number, [6] or [5], of the D cation. The general formula for an H-sheet is [Dφap{T2nΘbr(3n–2)Θap2nΘl4}φt0–1], where φt (written after the T-sheet) occurs on the outside of the H-sheet and may be involved in linkage between adjacent H–O–H blocks. The H-sheet links via its apical anions to the O-sheet, giving the general formula of an H–O–H block as [M(3n+1)(DφapΨn{T2nΘ(5n+2)}φt0–1)2]. These H–O–H blocks may link directly or indirectly through the φt anions of the (DΘl4φapφt) octahedra, giving S(2;n) = Xi[M(3n+1)Ψ2n(D2φap2{T2nΘbr(3n–2)Θap2nΘl4}2)φt0–2]. Combining the expressions for the structure-generating functions gives a single function for T–O–T and H–O–H structures:

S(N;n) = Xi[M(3n+2N–3)?2(n+N–2)(D2(N–1)f2ap(N–1){T2nT(3n–N)brT2napT2N1}2)f0–2(N–1)t]

This expression also generates mixed-ribbon polysomatic structures. Thus S(1;2+3) gives the chemical composition and structure of the mixed-chain pyribole chesterite, and S(2;1+4) gives the chemical composition and structure of the mixed-chain H–O–H mineral, veblenite.

Schäferite, NaCa2Mg2(V5+O4)3; palenzonaite, NaCa2Mn22+(V5+O4)3; berzeliite, NaCa2Mg2(As5+O4)3; and manganberzeliite, NaCa2Mn2+2(As5+O4)3, are cubic minerals with garnet structures (space group Iad) in which tetrahedrally coordinated V5+ and/or As5+ at the Z site are charge balanced by disordered Na+ and Ca2+ at the X site, and divalent Mg2+ and Mn2+ cations at the octahedrally coordinated Y site. The crystal chemistry of palenzonaite (from the Molinello and Gambatesa mines, Italy, and the Fianel mine, Switzerland), berzeliite (from Långban, Sweden, and Montaldo, Italy), and manganberzeliite (from Varenche, Italy, and the Gozaisho mine, Japan) were studied by electron microprobe analysis and single-crystal X-ray diffraction methods. Structure refinements converged to R1 values of 1.36–2.42%. The tetrahedral site in these garnet structures is mainly occupied by pentavalent As5+ or V5+ (only up to about 20% randomly distributed Si4+ is present). Charge balance is maintained by variations in the Ca/Na ratio at the X site. Heterovalent substitution (Na+ ↔ Ca2+) at the distorted square antiprism X site in vanadate- and arsenate-bearing garnets allows full occupancy of the octahedral Y site by divalent cations (primarily Mg2+ and Mn2+). There is a positive correlation between the <Z–O> and <Y–O> bond lengths and the mean ionic radii of the substituent elements, but there is no correlation between the <X–O> bond length and the variable Na/Ca site occupancy. The ionic radii of octahedrally coordinated Mg2+ and Mn2+ are such that the shared octahedral–dodecahedral edges are similar in length to the unshared octahedral edges, which is a measure of lattice distortion in garnet structures.

The rocks of the Jasra intrusive complex (Shillong Plateau, northeastern India) include phlogopite clinopyroxenites (with olivine or perovskite relics), alkali gabbros/monzodiorites, syenites and nepheline syenites. They have a potassic affinity (Na2O/K2O ∼1), and their mineralogy is dominated by clinopyroxene with which phlogopite, olivine, amphibole, feldspars, feldspathoids, oxides, orthopyroxenes, perovskite, titanite and other accessory phases are variably associated. The Jasra intrusive rocks are cumulates derived from at least two distinct magmatic liquids. The potassic affinity of the Jasra rocks differs from the nearby Sung Valley ijolitic-carbonatitic complex and from the ultrapotassic lamproitic rocks of the Damodar Valley, which are of approximately the same age. This suggests major variability in the mantle sources of small-volume alkaline volcanism in the Early Cretaceous of northeastern India.

Ianbruceite, ideally [Zn2(OH)(H2O)(AsO4)](H2O)2, is a new supergene mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia. It occurs as thin platy crystals up to 80 μm long and a few μm thick, which form flattened aggregates up to 0.10 mm across, and ellipsoidal aggregates up to 0.5 mm across. It is associated with coarse white leiteite, dark blue köttigite, minor legrandite and adamite. Ianbruceite is sky blue to very pale blue with a white streak and a vitreous lustre; it does not fluoresce under ultraviolet light. It has perfect cleavage parallel to (100), is flexible, and deforms plastically. The Mohs hardness is 1 and the calculated density is 3.197 g cm-3. The refractive indices are α = 1.601, β = 1.660, γ = 1.662, all ±0.002; 2Vobs = 18(2)°, 2Vcalc = 20°, and the dispersion is r < v, weak. Ianbruceite is monoclinic, space group P21/c, a = 11.793(2), b = 9.1138(14), c = 6.8265(10) Å, β = 103.859(9)°, V = 712.3(3) Å3, Z = 4, a:b:c = 1.2940:1:0.7490. The seven strongest lines in the X-ray powder diffraction pattern [d(Å), I, (hkl)] are as follows: 11.29, 100, (100); 2.922, 17, (130); 3.143, 15, (202); 3.744, 11, (300); 2.655, 9, (230); 1.598, 8, (152); 2.252, 7, (222). Chemical analysis by electron microprobe gave As2O5 36.27, As2O3 1.26, Al2O3 0.37, ZnO 49.72, MnO 0.32, FeO 0.71, K2O 0.25, H2Ocalc 19.89, sum 108.79 wt.%; the very high oxide sum is due to the fact that the calculated H2O content is determined from crystal-structure analysis, but H2O is lost under vacuum in the electron microprobe.

The crystal structure of ianbruceite was solved by direct methods and refined to an R1 index of 8.6%. The As is tetrahedrally coordinated by four O anions with a mean As O distance of 1.687 Å. Zigzag [[5]Zn[6]Znϕ7] chains extend in the c direction and are linked in the b direction by sharing corners with (AsO4) tetrahedra to form slabs with a composition [Zn2(OH)(H2O)(AsO4)]. The space between these slabs is filled with disordered (H2O) groups and minor lone-pair stereoactive As3+. The ideal formula derived from chemical analysis and crystal-structure solution and refinement is [Zn2(OH)(H2O)(AsO4)](H2O)2.

Hielscherite, ideally Ca3Si(OH)6(SO4)(SO3)·11H2O, (IMA 2011-037) is the first ettringite-group mineral with essential sulfite. We have identified a continuous natural solid-solution series from endmember thaumasite, Ca3Si(OH)6(SO4)(CO3)·12H2O, to a composition with at least 77 mol.% endmember hielscherite. In this series, the SO3:CO3 ratio is variable, whereas the SO4 content remains constant. Compositions with more than 50 mol.% endmember hielscherite have only been found at Graulay quarry near Hillesheim in the western Eifel Mountains, Rhineland-Palatinate, where they occur with phillipsite-K, chabazite-Ca and gypsum in cavities in alkaline basalt. Sulfite-rich thaumasite has been found in hydrothermal assemblages in young alkaline basalts in two volcanic regions of Germany: it is widespread at Graulay quarry and occurs at Rother Kopf, Schellkopf and Bellerberg quarries in Eifel district; it has also been found at Zeilberg quarry, Franconia, Bavaria. Hielscherite forms matted fibrous aggregates up to 1 cm across and groups of acicular to prismatic hexagonal crystals up to 0.3 × 0.3 × 1.5 mm. Individual crystals are colourless and transparent with a vitreous lustre and crystal aggregates are white with a silky lustre. The Mohs hardness is 2–2½. Measured and calculated densities are Dmeas = 1.82(3) and Dcalc = 1.79 g cm–3. Hielscherite is optically uniaxial (–), ω = 1.494(2), ε = 1.476(2). The mean chemical composition of holotype material (determined by electron microprobe for Ca, Al, Si, and S and gas chromatography for C, H and N, with the S4+:S6+ ratio from the crystal-structure data) is CaO 27.15, Al2O3 2.33, SiO2 7.04, CO2 2.71, SO2 6.40, SO3 12.91, N2O5 0.42, H2O 39.22, total 98.18 wt.%. The empirical formula on the basis of 3 Ca atoms per formula unit is Ca3(Si0.73Al0.28)Σ1.01(OH)5.71(SO4)1.00(SO3)0.62(CO3)0.38(NO3)0.05·10.63H2O. The presence of sulfite was confirmed by crystal-structure analysis and infrared and X-ray absorption near edge structure spectra. The crystal structure of sulfite-rich thaumasite from Zeilberg quarry was solved by direct methods based on single-crystal X-ray diffraction data (R1 = 0.064). The structure of hielscherite was refined using the Rietveld method (Rwp = 0.0317). Hielscherite is hexagonal, P63, a = 11.1178(2), c = 10.5381(2) Å, V = 1128.06(4) Å3 and Z = 2. The strongest reflections in the X-ray powder pattern [(d, Å (I)(hkl)] are: 9.62(100)(010,100); 5.551(50)(110); 4.616(37)(012,102); 3.823(64)(112); 3.436(25)(211), 2.742(38)(032,302), 2.528(37)(123,213), 2.180(35)(042,402;223). In both hielscherite and sulfite-rich thaumasite, pyramidal sulfite groups occupy the same site as trigonal carbonate groups, with analogous O sites, whereas tetrahedral sulfate groups occupy separate positions. Hielscherite is named in honour of the German mineral collector Klaus Hielscher (b. 1957).

Raberite, ideally Tl5Ag4As6SbS15, is a new mineral from Lengenbach quarry in the Binn Valley, Valais, Switzerland. It occurs very rarely as euhedral crystals up to 150 m m across associated with yellow needle-like smithite, realgar, hatchite and probable trechmannite, edenharterite, jentschite and two unidentified sulfosalts. Raberite is opaque with a metallic lustre and has a dark brown–red streak. It is brittle with a Vickers hardness (VHN10) of 52 kg mm–2 (range 50–55) corresponding to a Mohs hardness of 2½–3. In reflected light raberite is moderately bireflectant and very weakly pleochroic from light grey to a slightly greenish grey. It is very weakly anisotropic with greyish to light blue rotation tints between crossed polars. Internal reflections are absent. Reflectance percentages for the four COM wavelengths [listed as Rmin, Rmax, (λ)] are 30.6, 31.8 (471.1 nm), 28.1, 29.3 (548.3 nm), 27.1, 28.0 (586.6 nm), and 25.8, 26.9 (652.3 nm).

Raberite is triclinic, space group P1, with a = 8.920(1), b = 9.429(1), c = 20.062(3) Å, α = 79.66(1), β = 88.84(1), γ = 62.72(1)º, V = 1471.6(4) Å3 and Z = 2. The crystal structure [R1 = 0.0827 for 2110 reflections with I > 2σ(I)] consists of columns of nine-coordinate Tl atoms forming irregular polyhedra extending along [001] and forming sheets parallel to (010). The columns are decorated by cornersharing MS3 pyramids (M = As, Sb) and linked by AgS3 triangles. Of the seven M positions, one is dominated by Sb and the others by As; the mean M-S bond distances reflect As ↔ Sb substitution at these sites.

The eight strongest lines in the powder diffraction pattern [dcalc in Å (I) (hkl)] are: 3.580 (100) (13); 3.506 (58) (23); 3.281 (73) (006); 3.017 (54) (3); 3.001 (98) (133); 2.657 (51) (226); 2.636 (46) (300); 2.591 (57) (330). A mean of 9 electron microprobe analyses gave Tl 39.55(13), Ag 18.42(8), Cu 0.06(2), As 17.08(7), Sb 5.61(6), S 19.15(11); total 99.87 wt.%, which corresponds to Tl4.85Ag4.28Cu0.02As5.72Sb1.16S14.97 with 31 atoms per formula unit. The new mineral has been approved by the IMA-CNMNC Commission (IMA 2012-017) and is named for Thomas Raber, an expert on Lengenbach minerals.

Aluminium-bearing strunzite, [Mn0.65Fe0.26Zn0.08Mg0.01]2+[Fe1.50Al0.50]3+(PO4)2(OH)2·6H2O, occurs as fibrous aggregates in a crystallographically oriented association with jahnsite on altered zwieselite samples from the phosphate pegmatite at Hagendorf Süd, Bavaria, Germany. Synchrotron X-ray data were collected from a 3 μm diameter fibre and refined in space group P to R1 = 0.054 for 1484 observed reflections. The refinement confirmed the results of chemical analyses which showed that one quarter of the trivalent iron in the strunzite crystals is replaced by aluminium. The paragenesis revealed by scanning electron microscopy, in combination with chemical analyses and a crystal-chemical comparison of the strunzite and jahnsite structures, are consistent with strunzite being formed from jahnsite by selective leaching of (100) metal—phosphate layers containing large divalent Ca and Mn atoms.

Type specimens of the molybdoarsenates betpakdalite, natrobetpakdalite and obradovicite and the molybdophosphates mendozavilite, paramendozavilite and melkovite, and similar material from other sources, have been examined in an effort to elucidate the relations among these phases, which we designate as the heteropolymolybdate family of minerals. Using electron microprobe analysis, X-ray powder diffraction and single-crystal X-ray diffraction with crystal structure determination where possible, it was found that natrobetpakdalite, mendozavilite and melkovite are isostructural with betpakdalite and that obradovicite has a closely related structure.

The betpakdalite and obradovicite structure types are based on frameworks containing four-member clusters of edge-sharing MoO6 octahedra that link by sharing corners with other clusters, with Fe3+O6 octahedra and with PO4 or AsO4 tetrahedra (T). The structures differ in the linkages through the Fe3+O6 octahedra, which produce different but closely related framework configurations. The structures contain two types of non-framework cation sites, which are designated A and B. In general, there are two or more A sites partially occupied by disordered, generally larger cations that are coordinated to O atoms in the framework and to H2O molecules. The B site is occupied by a smaller cation that is octahedrally coordinated to H2O molecules. The general formula for minerals with either the betpakdalite or the obradovicite structure is: [A2(H2O)nB(H2O)6][Mo8T2Fe3+3O30+7(OH)7–x], where x is the total charge of the cations in the A and B sites (+3 to +7) and n is variable, ideally 17 for arsenates and 15 for phosphates. The ideal total number of A cations is defined as 2 in the general formula, but varies from 1 to 3.8 in analysed samples. Dominant cations at the A site include K, Na and Ca and at the B site Na, Ca, Mg, Cu and Fe. The combinations that have been identified in this study define six new heteropolymolybdate species.

A suffix-based nomenclature scheme is established for minerals of the betpakdalite, mendozavilite and obradovicite groups, with the following root names based on the structure types and the T-site cations: betpakdalite (T = As), mendozavilite (T = P) and obradovicite (T = As). Two suffixes of the form -AB, corresponding to the dominant cations in the two different types of non-framework cation sites complete the species name. The historical name melkovite is retained rather than introducing mendozavilite-CaCa.

Our investigation of the paramendozavilite type specimen revealed no paramendozavilite, but an apparently closely related new mineral; however, another sample of paramendozavilite analysed had K > Na.

The weathering and oxidation of mine tailings has the potential to contaminate water and soil with toxic elements. To understand the mechanisms, extent and products of the long-term weathering of complex Bolivian tailings from the Cerro Rico de Potosí, and their effects on As, Pb, P and Sb cycling, three-year long laboratory column experiments were carried out to model 20 years of dry- and wet-season conditions in the Pilcomayo basin. Chemical analysis of the leachate and column solids, optical mineralogy, X-ray diffraction, scanning electron microscopy, electron probe microanalysis, microscale X-ray absorption near edge structure spectroscopy, Bureau Commun de Référence sequential extraction and water-soluble chemical extractions, and speciation modelling have shown that the weathering of As-bearing pyrite and arsenopyrite, resulted in a loss of 13–29% of the original mass of As. By contrast, Pb and Sb showed much lower mass losses (0.1–1.1% and 0.6–1.9%, respectively) due to the formation of insoluble Pb- and Sb(V)-rich phases, which were stable at the low pH (~2) conditions that prevailed by the end of the experiment. The experiment also demonstrated a link between the cycling of As, Sb, and the oxidation of Fe(II)-bearing sphalerite, which acted as a nucleation point for an Fe-As-Sb-O phase. Phosphorus was relatively immobile in the tailings columns (up to 0.3% mass loss) but was more mobile in the soil-bearing columns (up to 10% mass loss), due to the formation of soluble P-bearing minerals or mobilization by organic matter. These results demonstrate the influence of mine tailings on the mobility of P from soils and on the potential contamination of ecosystems with As, and strongly suggest that these materials should be isolated from fluvial environments.

Thirty pyrite samples from a wide range of localities were analysed using relative comparator and k0 neutron activation analysis (NAA) techniques at the University of Missouri Research Reactor, Columbia, Missouri, USA (MURR) and the Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia (ANSTO), respectively. Statistical analyses of the trace-element data produced by the two methods showed a generally good correlation, with the majority of elemental concentrations of paired data reported by MURR and ANSTO being indistinguishable at a 0.05 significance level. Trace-element analyses of pyrite from Navajún in Spain by both techniques compare well with published data. There is evidence for contamination by Al, Na and Ti in one set of samples, this is likely to have been introduced by contact with a plastic used in sample preparation.

Rumseyite, ideally [Pb2OF]Cl, is a new mineral species which is associated with calcite, cerussite, diaboleite, hydrocerussite and undifferentiated Mn oxides in a small cavity in 'hydrocerussite' from a manganese pod at Merehead quarry, Somerset, England. Rumseyite is tetragonal, I4/mmm, a = 4.065(1), c = 12.631(7) Å, V = 208.7(1) Å3, Z = 2. The mineral is translucent pale orange-brown with a white streak and vitreous lustre. It is brittle with perfect {100} cleavage; Dcalc = 7.71 g cm–3 (for the ideal formula, [Pb2OF]Cl). The mean refractive index in air at 589 nm is 2.15. The six strongest reflections in the X-ray powder-diffraction pattern [dmeas in Å, (Irel), (hkl)] are as follows: 2.923(100)(013), 2.875(68)(110), 3.848(41)(011), 6.306(17)(002), 1.680(14)(123), 2.110(12)(006). The crystal structure of rumseyite is based on alternating [OFPb2] and Cl layers. Rumseyite is related to other layered Pb oxyhalides. Fluorine and oxygen are statistically disordered over one crystallographic site. Rumseyite is named in honour of Michael Scott (Mike) Rumsey (1980– ), Curator and Collections Manager at the NHM (London), who discovered the mineral. The mineral and name have been approved by the IMA Commission on New Mineral Names and Classification (IMA 2011-091). The holotype specimen is in the collections of the Natural History Museum, London (specimen number BM1970,110).

Synchrotron X-ray powder diffraction data have been collected on three synthetic leucite analogues with the general formula Cs2XSi5O12(X = Cd, Cu, Zn) between 295 and 1173 K. All three samples have the orthorhombic Pbca leucite structure at room temperature with ordered framework T-site cations. The sample with X = Cd retains the Pbca structure over the whole of the investigated temperature range. The sample with X = Cu also retains the Pbca structure, but there is a transition to a less distorted structure with a larger unit-cell volume at ∼333 K. The sample with X = Zn shows evidence for a transition to a previously unknown Pa cubic structure, with some T-site cation disorder, at 566 K, on heating. This transition is reversible on cooling to 633 K.

Layered double hydroxide (LDH) compounds are characterized by structures in which layers with a brucite-like structure carry a net positive charge, usually due to the partial substitution of trivalent octahedrally coordinated cations for divalent cations, giving a general layer formula [(M1–x2+M3+x)(OH)2]x+. This positive charge is balanced by anions which are intercalated between the layers. Intercalated molecular water typically provides hydrogen bonding between the brucite layers. In addition to synthetic compounds, some of which have significant industrial applications, more than 40 mineral species conform to this description. Hydrotalcite, Mg6Al2(OH)16[CO3]·4H2O, as the longest-known example, is the archetype of this supergroup of minerals. We review the history, chemistry, crystal structure, polytypic variation and status of all hydrotalcite-supergroup species reported to date. The dominant divalent cations, M2+, that have been reported in hydrotalcite supergroup minerals are Mg, Ca, Mn, Fe, Ni, Cu and Zn; the dominant trivalent cations, M3+, are Al, Mn, Fe, Co and Ni. The most common intercalated anions are (CO3)2–, (SO4)2– and Cl–; and OH–, S2– and [Sb(OH)6]– have also been reported. Some species contain intercalated cationic or neutral complexes such as [Na(H2O)6]+ or [MgSO4]0. We define eight groups within the supergroup on the basis of a combination of criteria. These are (1) the hydrotalcite group, with M2+:M3+ = 3:1 (layer spacing ∼7.8 Å); (2) the quintinite group, with M2+:M3+ = 2:1 (layer spacing ∼7.8 Å); (3) the fougèrite group, with M2+ = Fe2+, M3+ = Fe3+ in a range of ratios, and with O2– replacing OH– in the brucite module to maintain charge balance (layer spacing ∼7.8 Å); (4) the woodwardite group, with variable M2+:M3+ and interlayer [SO4]2 –, leading to an expanded layer spacing of ∼8.9 Å; (5) the cualstibite group, with interlayer [Sb(OH)6]– and a layer spacing of ∼9.7 Å; (6) the glaucocerinite group, with interlayer [SO4]2– as in the woodwardite group, and with additional interlayer H2O molecules that further expand the layer spacing to ∼11 Å; (7) the wermlandite group, with a layer spacing of ∼11 Å, in which cationic complexes occur with anions between the brucite-like layers; and (8) the hydrocalumite group, with M2+ = Ca2+ and M3+ = Al, which contains brucite-like layers in which the Ca:Al ratio is 2:1 and the large cation, Ca2+, is coordinated to a seventh ligand of 'interlayer' water.

The principal mineral status changes are as follows. (1) The names manasseite, sjögrenite and barbertonite are discredited; these minerals are the 2H polytypes of hydrotalcite, pyroaurite and stichtite, respectively. Cyanophyllite is discredited as it is the 1M polytype of cualstibite. (2) The mineral formerly described as fougèrite has been found to be an intimate intergrowth of two phases with distinct Fe2+:Fe3+ ratios. The phase with Fe2+:Fe3+ = 2:1 retains the name fougèrite; that with Fe2+:Fe3+ = 1:2 is defined as the new species trébeurdenite. (3) The new minerals omsite (IMA2012-025), Ni2Fe3+(OH)6[Sb(OH)6], and mössbauerite (IMA2012-049), Fe3+6O4(OH)8[CO3]·3H2O, which are both in the hydrotalcite supergroup are included in the discussion. (4) Jamborite, carrboydite, zincaluminite, motukoreaite, natroglaucocerinite, brugnatellite and muskoxite are identified as questionable species which need further investigation in order to verify their structure and composition. (5) The ranges of compositions currently ascribed to motukoreaite and muskoxite may each represent more than one species. The same applies to the approved species hydrowoodwardite and hydrocalumite. (6) Several unnamed minerals have been reported which are likely to represent additional species within the supergroup.

This report has been approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association, voting proposal 12-B.

We also propose a compact notation for identifying synthetic LDH phases, for use by chemists as a preferred alternative to the current widespread misuse of mineral names.

Zincalstibite-9R, a new polytype in the hydrotalcite supergroup is reported from the Monte Avanza mine, Italy. It occurs as pale blue curved disc-like tablets flattened on {001} intergrown to form rosettes typically less than 50 μm in diameter, with cyanophyllite and linarite in cavities in baryte. Zincalstibite-9R is uniaxial (–), with refractive indices ω = 1.647(2) and ε = 1.626(2) measured in white light. The empirical formula (based on 12 OH groups) is (Zn1.092+Cu0.872+Al0.04)Σ2.00Al1.01(Sb0.975+Si0.02)Σ0.99(OH)12, and the ideal formula is (Zn,Cu)2Al(OH)6[Sb(OH)6]. Zincalstibite-9R crystallizes in space group R, with a = 5.340(2), c = 88.01(2) Å, V = 2173.70(15) Å3 and Z = 9. The crystal structure was refined to R1 = 0.0931 for 370 unique reflections [Fo > 4σ(F)] and R1 = 0.0944 for all 381 unique reflections. It has the longest periodic layer stacking sequence for a layered double hydroxide compound reported to date.

Omsite (IMA 2012-025) is a new mineral from the Correc d'en Llinassos, Oms, Pyrénées-Orientales Department, France. It occurs as bright yellow to amber yellow discoidal tablets, flattened on {001}, which form rosettes typically 50–100 μm in diameter. Omsite generally crystallizes on siderite without associated supergene minerals; it occurs less commonly with glaukosphaerite. Crystals have a vitreous to resinous lustre, and are transparent to translucent. Omsite is not fluorescent in either short-wave or long-wave ultraviolet light. It has an estimated hardness of 3 on the Mohs' scale, is brittle with an irregular fracture, and has one poor cleavage on {001}. The calculated density is 3.378 g cm–3. Crystals are uniaxial (–), with indices of refraction of ω = 1.728(3) and ε = 1.66(1), measured in white light. Pleochroism is ω = orange-yellow, ε = pale orange-yellow; ω > ε. The empirical formula [based on 12 (OH + Cl) p.f.u.] is (Ni1.0992+Cu0.6652+Mg0.107Fe0.0453+)Σ 1.916Fe1.0003+(Sb0.9475+As0.072Na0.029)Σ1.048OH11.967Cl0.033. Omsite crystallizes in space group P, with unit-cell parameters a = 5.3506(8), c = 19.5802(15) Å, V = 485.46(10) Å3 and Z = 2 determined by single crystal X-ray diffraction. The five strongest lines in the X-ray powder diffraction pattern [d in Å, (Irel), (hkl)] are as follows: 4.901, (100), (004); 4.575, (83), (011); 2.3539, (81), (11); 1.8079, (48), (11); 3.781, (34), (103). The crystal structure was solved to R1 = 0.0896 for 356 observed reflections [Fo>4σFo] and 0.1018 for all the 469 unique reflections. Omsite is a layered double hydroxide (LDH) mineral, with a topology consistent with members of the hydrotalcite supergroup and cualstibite group.