Clogauite, ideally PbBi4Te4S3 is the new n = 1 member of the aleksite series, PbnBi4Te4Sn+2, where n is the homologue number. Clogauite is named from the type locality, the Clogau gold mine, Dolgellau Gold belt, Gwynedd, North Wales, United Kingdom. The mineral and name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2023–062). The aleksite series is an accretional homologous series in which each member is derived from the same 5-atom tetradymite archetype. Clogauite crystallises in the trigonal crystal system (space group: P$\bar{3}$m1, #164). Three distinct polytypes of clogauite are recognised, corresponding to identical chemistry but different layer sequences, expressed as (57), (5559) and (557.559), respectively, in reference to the number of atoms in individual layer sequences. These are clogauite-12H, a = 4.277(4) Å, c = 23.46(14) Å, V = 371.598 Å3 and Z = 1; clogauite-24H, a = 4.278(4) Å, c = 46.88(31) Å, V = 743.053 Å3 and Z = 2; and clogauite-36H, a = 4.278(4) Å, c = 70.36(32) Å, V = 1115.283 Å3 and Z = 3. Clogauite is opaque, with a pale grey colour in reflected light. Reflectance is higher than tetradymite or galena. Bireflectance and anisotropy are strong. Structural data were determined from measurement of atomic-scale HAADF STEM imaging showing the internal arrangement of component atoms and characteristic selected area electron diffraction patterns for each polytype. The structures were then further constrained from ab initio total energy calculations and structure relaxation using density functional theory (DFT) using the measured parameters as input data. The relaxed crystal structure for each polytype was modelled to generate crystallographic information files (cif). STEM and electron diffraction simulations based on the crystallographic information data obtained from the DFT calculations show an excellent match to the empirical measurements.

Markwelchite, ideally TlPbSbS3, is a new mineral from the hydrothermal deposit of Jas Roux, Hautes-Alpes, France. It occurs as a black anhedral crystal associated closely with protochabournéite. Microhardness measurements (VHN15) gave a mean value of 197 kg/mm2 corresponding to a Mohs hardness of ~3–4. In plane-polarised incident light, markwelchite is grey in colour. Under crossed polars, it is distinctly anisotropic with greyish white to bluish rotation tints, with bright red internal reflections. Reflectance percentages (Rmin and Rmax) are: 28.5, 31.5 (471.1 nm); 28.3, 30.7 (548.3 nm); 27.9, 30.3 (586.6 nm); and 27.6, 29.8 (652.3 nm). The mean of 5 electron microprobe spot analyses gave Tl 34.67(45), Pb 31.86(25), Sb 15.06(15), As 2.37(5), S 15.35(20), total 99.31 wt.%, corresponding, on the basis of a total of 6 atoms per formula unit and structural results, to Tl1.063Pb0.964(Sb0.775As0.198)Σ0.973S3.000. Single-crystal X-ray diffraction studies revealed that markwelchite is isotypic with richardsollyite, TlPbAsS3. It is monoclinic, space group P21/c, with the following unit-cell parameters: a = 8.9144(3), b = 8.4513(3), c = 8.6511(3) Å, β = 108.723(4)°, V = 617.27(4) Å3 and Z = 4. The five strongest observed powder-diffraction lines [d in Å (Irel)(hkl)] are: 3.88 (100)($\bar{2}$11); 3.78 (90)(210); 3.29 (90)(102); 2.73 (85)($\bar{1}$13); and 2.93 (75)(022). The crystal structure can be described as formed by (100) [Me2(SbS3)]– layers sandwiching the Me1+ cations. The Me1 site has a seven-fold coordination, whereas the Me2 site has an 6+2 coordination corresponding to a distorted, bicapped trigonal prismatic coordination, and the Sb site displays a trigonal pyramidal coordination with three S atoms and Sb at the apex.

The name markwelchite honours Dr Mark D. Welch of the Natural History Museum, London, UK.

The new mineral has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2024–001). A discussion on the relationships between markwelchite and synthetic TlPbSbS3 is also provided.

The high-pressure behaviour of inderborite [ideally CaMg[B3O3(OH)5]2(H2O)4⋅2H2O, space group C2/c with a ≈ 12.14, b ≈ 7.43, c ≈ 19.23 Å and β ≈ 90.3° at room conditions] has been studied by two in situ single-crystal synchrotron X-ray diffraction experiments up to ~10 GPa, using He as pressure-transmitting fluid. Between 8.11(5) and 8.80(5) GPa, inderborite undergoes a first-order phase transition to its high-pressure polymorph, inderborite-II (with a ≈ 11.37, b ≈ 6.96, c ≈ 17.67 Å, β ≈ 96.8° and ΔV ≈ 7.0%, space group unknown). The isothermal bulk modulus (KV0 = β−1P0,T0, where βP0,T0 is the volume compressibility coefficient) of inderborite was found to be KV0 = 41(1) GPa. The destructive nature of the phase transition prevented any structure resolution of inderborite-II or even the continuation of the experiments at pressures higher than 10.10(5) GPa. In the pressure range 0–8.11(5) GPa, the compressional anisotropy of inderborite, indicated by the ratio between the principal components of the Eulerian finite unit-strain ellipsoid, is ɛ1:ɛ2:ɛ3 = 1.4:1.05:1. The deformation mechanisms at the atomic scale in inderborite are here described. Our findings support the hypothesis of a quasi-linear correlation between the total H2O content and P-stability range in hydrated borates, as the pressure at which inderborite undergoes the phase transition falls in line with most of the hydrate borates studied at high-pressure so far.

Zipserite is a new mineral species discovered in a sample collected from the old mine dumps of the abandoned epithermal deposit Nagybörzsöny in Hungary. Zipserite occurs as anhedral to subhedral, lath-like grains, up to 500 μm in size, in hydrothermally strongly altered rocks. It is found at a contact between bismuth and bismuthinite, also associated with rare ikunolite and joséite-A. Zipserite is silvery white with a metallic lustre. Mohs hardness is ca. 2–3 and the calculated density is 7.815 g.cm–3. In reflected light, zipserite is grey–white, with colour and reflectance essentially matching those of bismuthinite. Bireflectance is weak, internal reflections not present. Anisotropy is moderately strong, with dark blue and grey colours of anisotropy. Reflectance values for the four Commission on Ore Mineralogy wavelengths of zipserite in air [Rmax, Rmin (%) (λ in nm)] are: 48.4, 46.4 (470); 47.8, 45.9 (546); 47.8, 45.8 (589); and 47.5, 45.6 (650). The empirical formula, based on electron-microprobe analyses, is (Bi4.74Pb0.31)Σ5.05(S3.38Se0.56Te0.02)Σ3.96, that can be simplified as Bi5(S,Se)4. The ideal end-member formula of zipserite is Bi5S4, which requires Bi 89.07 and S 10.93, total 100 wt.%. Zipserite possesses a fascinating crystal structure. The average structure is trigonal, with space group P$\bar{3}$m, a = 4.162(1) Å, c = 16.397(1) Å, V = 245.94(4) Å3 and Z = 2. The structure is built by the alternation of a double bismuth layer Bi2 and the Bi3S4 block which is a three octahedra thick layer. Its general formula can be expressed as Bi2 + Bi3S4, which corresponds directly to the observed stacking. At 98 K, the structure can be described using the superspace formalism with an R-centred trigonal unit cell a = 4.209(2) Å, c0 = 5.616(6) Å, a modulation vector q ≈ 4/3 c* and the superspace group R$\bar{3}$m(00γ)00. Zipserite is not only a new mineral but also the first named member of a new sub-group of compounds within the broader family of bismuth chalcogenides, characterised by complex stacking of structural units (Bi2 layers and Bi3S4 blocks). Some of these phases are being investigated as promising thermoelectric materials and synthetic analogues of zipserite could also be inspected for similar physical properties.

Qeltite (IMA2021–032), ideally Ca3Ti(Fe2Si)Si2O14, was found in gehlenite–rankinite–wollastonite paralava from a pyrometamorphic rock of the Hatrurim Complex at Nabi Musa locality, Judean Desert, West Bank, Palestine. It generally occurs as light-brown flattened crystals up to 40–50 μm in length and less than 5 μm in thickness. Its aggregates reach 100–200 μm in size. Its empirical crystal chemical formula based on 14 O is: (Ca2.96Sr0.02Mn0.01)Σ2.99Ti4+(Fe3+1.59Si0.60Al0.43Ti4+0.38Cr0.01)Σ3.01(Si1.99P0.01)Σ2O14. The strongest reflections in its calculated X-ray diffraction pattern are [d, Å, (I, %), hkl]: 3.12, (100), 111; 2.85, (61), 201; 2.85, (48), 021; 2.32, (45), 211; 6.93, (31), 100; and 1.81, (30), 212. Qeltite is trigonal and crystallises in the noncentrosymmetric P321 space group, with a = 8.0077(5) Å, c = 4.9956(4) Å, V = 277.42(4) Å3 and Z = 1. Its microhardness VHN25 is 708(17) kg/mm2 and its hardness on the Mohs scale is ~6. Its calculated density is 3.48 g/cm3. It was found in fine-grained mineral aggregates within coarse-grained main minerals of rankinite–gehlenite paralava with subordinate wollastonite, Ti-bearing andradite and kalsilite. In these aggregates, the mineral is associated with khesinite, paqueite and pseudowollastonite, indicating a high-temperature genesis (~1200°C). Its crystallisation can be compared with the crystallisation of minerals containing refractory inclusions in meteorites.

Ermeloite is a new aluminium phosphate mineral from Galicia, Spain, in the northwest of the Iberian Peninsula. It is the third formally recognised mineral discovered in Galicia since morenosite and cervantite in the 19th Century. The name and symbol (Erm) were approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2021–017a) in recognition of the geographical location where it was found. The mineral occurs as a light blue to white fine aggregate over quartz and microcline associated with wardite. Crystals of ~0.04 mm are transparent and have a waxy lustre. The simplified empirical formula determined using electron microprobe analysis is Al1.02P0.95F0.06O3.88⋅1.06 H2O, which is near to the ideal formula Al(PO4)⋅H2O. The mineral is an alteration product within a phosphate pegmatite. Ermeloite is the second phosphate isostructural with the sulfates of the kieserite group. Single-crystal X-ray diffraction showed that ermeloite crystallises in the monoclinic C2/c space group with cell parameters a = 6.5371(4) Å, b = 7.5670(5) Å, c = 7.1146(5) Å, β = 115.335(2)°, V = 318.08(4) Å3 and Z = 4 at room temperature. Comparative analysis of the crystallographic data, with isostructural phosphates, revealed an interesting behaviour for these compounds.

The lithium sodium borosilicate jadarite, LiNaSiB3O7(OH), was first identified in 2007 in the Jadar basin, Serbia, where it forms the principal ore mineral of one of Europe's largest Li deposits. We report the successful application of the dry-gel conversion technique (DGC) to synthesise a jadarite analogue, via a dry-gel precursor made using sol-gel synthesis and the inclusion of the structure directing agent tetraethylammonium hydroxide (TEAOH). Pawley refinement of powder X-ray diffraction (PXRD) data collected on the synthetic sample was carried out using a monoclinic unit cell in space group P21/c (Whitfield et al., 2007), and gave refined unit cell parameters of a = 6.824(3) Å, b = 13.882(5) Å, c = 7.735(3) Å and β = 124.37(1)° (Rwp = 9.22). Inductively-coupled plasma optical emission spectroscopy (ICP–OES) on the synthetic sample confirmed an empirical formula of Li1.07Na1.40Si0.79B3O7.32(OH), based on three B atoms per formula unit (apfu). The synthetic product was found to be deficient in Si compared to natural jadarite from analysis of PXRD and ICP–OES data. Fourier-transform infrared spectroscopy (FTIR) showed that synthetic jadarite has peaks at 1415 and 1342 cm–1 and between 1180 and 900 cm–1, which are attributed to the presence of trigonal (BO3) and tetrahedral (BO4) borate groups characteristic of the natural jadarite structure, as well as a broad peak at 3441 cm–1 due to the presence of residual TEAOH. Scanning electron microscopy showed similarities in the morphologies between synthetic and natural jadarite particles.

Tetrahedrite-(Cu), Cu12Sb4S13, has been approved as a new mineral species (IMA2022–078) from the Bankov magnesite deposit near Košice, Slovak Republic where it occurs as anhedral grains, up to 0.4 mm across, associated with skinnerite, chalcostibite, famatinite, tetrahedrite-(Fe) and zoned aggregates of tennantite-(Cu) to tennantite-(Fe). Tetrahedrite-(Cu) is steel-grey, with a metallic lustre. Mohs hardness is ca. 3½–4 and calculated density is 5.029 g.cm–3. In reflected light, tetrahedrite-(Cu) is isotropic and grey with a bluish shade. Reflectance data for the four COM wavelengths in air are [λ (nm): R (%)]: 470: 31.1; 546: 30.1; 589: 29.9; and 650: 28.1. The empirical formula, based on electron-microprobe data (mean of 17 spot analyses), is Cu11.42Zn0.26Fe0.19(Sb4.06As0.08)Σ4.14S12.99. The ideal formula is Cu6(Cu4Cu2)Sb4S13, which requires (in wt.%) Cu 45.76, Sb 29.23 and S 25.01, total 100.00. Tetrahedrite-(Cu) is cubic, I$\bar{4}$3m, with unit-cell parameters a = 10.3296(15) Å, V = 1102.2(5) Å3 and Z = 2. Its crystal structure was refined by single-crystal X-ray diffraction data to a final R1 = 0.0347 on the basis of 261 unique reflections with Fo > 4σ(Fo) and 22 refined parameters. Tetrahedrite-(Cu) is isotypic with other tetrahedrite-group minerals. Previous findings of tetrahedrite-(Cu) are reported and some nomenclature issues, related to the Fe and Cu oxidation states, are discussed. At the Bankov deposit, tetrahedrite-(Cu) is related to hydrothermal, most probably Alpine, solutions strongly enriched in Cu, Sb and S.

An attempt to compare and describe the differences in the electron density distribution between two phase structures of AlOOH has been made. High-resolution, high-pressure experiments with α-AlOOH diaspore were conducted using single-crystal synchrotron X-ray diffraction data. A multipole model of experimental electron density in the α-AlOOH single crystal was refined. Simultaneously, similar multipole refinement was conducted for another phase of diaspore (δ-AlOOH), this time based on a previously published data set. Both results were compared and supported by density functional theory (DFT) calculations. Although the results are affected by the limited quality of the data, it is clear that the phase transition caused significant changes in the shape and arrangement of the atomic basins.

Atomic basins are a much better tool to present subtle electron density distribution changes than traditional polyhedra. Straightforward comparison of datasets available in older scientific papers and current datasets is challenging because of differences in data quality and collection parameters. However, augmenting experimental data with computational results can help reveal important information in even incomplete datasets.

Daqingshanite in the Kamthai REE deposit (India) occurs as two paragenetic types: primary granular coarse grained crystals coexisting with primary carbocernaite, baryte and bastnäsite; and as aligned micro-ovoid globules within clasts of Sr-bearing calcite. Carbocernaite forming trellis-type lamellae in some of these calcite clasts do not represent exsolution and are considered as replacement textures as they formed subsequent to daqingshanite. The origins of the textural relations of the microglobules of daqingshanite to their host Sr-calcite cannot be unambiguously determined, although an exsolution origin is not considered feasible. The textures are similar to those of ‘chalcopyrite disease’ and as such could be interpreted as replacement features formed in a low temperature carbothermal environment which should facilitate replacement. Given that daqingshanite is an early crystallising phase it is also possible that cotectic crystallisation with Sr-calcite occurred, followed by subsolidus re-equilibration with recrystallisation along specific crystallographic planes in the calcite. The Kamthai REE deposit is best described as a low temperature carbothermalite microbreccia consisting of a wide variety of clasts resulting from the autobrecciation of rocks formed during, and after, the magmatic to carbothermal transition of an undetermined parental calcite carbonatite-forming magma. Many clasts have been replaced by late stage La-enriched carbothermal fluids mixed with exogenous water during the final low-temperature stage of evolution of the deposit.

Škáchaite (IMA2022–143) is a new mineral species discovered in samples from the hydrothermal vein B117, shaft No. 6 at the Brod deposit of the uranium and base-metal Příbram ore district, central Bohemia, Czech Republic. Škáchaite is a Co-dominant member of the dolomite group and forms anhedral grains up to 50 μm in size and as 20–100 μm thick growth zones in škáchaite–dolomite crystals as a part of carbonate (dolomite, calcite, siderite, spherocobaltite, ankerite, kutnohorite and minrecordite) gangue, associated with native silver, sulfides and arsenides. Škáchaite is pale to bright pink with vitreous lustre. The Mohs hardness is ca. 3½–4, similar to other members of the dolomite group. The calculated density is 3.140 g.cm–3. Škáchaite is optically uniaxial (–); the indices of refraction are ω = 1.741(3) and ɛ = 1.535(3). On the basis of electron-microprobe analyses, its empirical formula is Ca1.00(Co0.45Mg0.38Ca0.08Fe0.05Mn0.03Zn0.01)Σ1.00(CO3)2. The ideal formula is CaCo(CO3)2, which requires (in wt.%) CaO 25.60, CoO 34.21, CO2 40.19, a total of 100.00. Škáchaite is trigonal, R$\bar{3}$, with unit-cell parameters a = 4.8177(18), c = 16.093(7) Å, V = 323.5(2) Å3 and Z = 3. The strongest reflections of the calculated powder X-ray diffraction pattern [d, Å, (Irel, %) hkl] are: 3.704 (13) 10$\bar{2}$; 2.896 (100) 104; 2.409 (15) 110; 2.019 (17) 202; 1.812 (19) 10$\bar{8}$; and 1.792 (16) 11$\bar{6}$. According to the single-crystal X-ray diffraction data (R1 = 0.0304 for 94 reflections with [I > 3σ(I)]), the crystal structure of škáchaite is isotypic with its Mg-analogue, dolomite. The Raman spectrum of škáchaite, as well as the tentative assignment of observed bands, are given in this paper. The mineral is named in honour of Pavel Škácha, a Czech mineralogist and curator of the mineralogical collection of the Mining Museum Příbram, Czech Republic.

Mineral species are known to be heterogeneously distributed throughout the Earth such that a relatively small number of minerals make up a large proportion of the lithosphere while the majority of all known minerals are rare and have been identified at only a small number of locations that frequently exhibit high levels of species richness. Intuitive understandings of mineral scarcity and abundance are reconsidered through the characterisation of the quantitative aspects of spatio-temporal trends in new mineral discovery. Using data drawn from online mineralogical databases, it is found that the Earth's mineral hotspots exhibit an exponential distribution of species abundance, while those same mineral hotspots exhibit a power-law distribution in the number of minerals first recognised at those locations. That is, locations rich in first occurrences are extremely rare, even when considering only the Earth's most species-rich mineral locations. Global distributions of mineral scarcity and abundance can be estimated from the number of mineral-location pairs for each species reported in a database. Two-thirds of all known species have been reported from ten or fewer locations and the frequency distribution of these mineral-location pairs exhibit a power-law distribution that extends with increasing dispersion over several orders of magnitude of mineral abundance. Initially, nearly all minerals are first reported from only their type locality. Over time, additional occurrences of newly discovered minerals are reported at an average rate of one new location per mineral every 5.5 years. As a result, the percentage of minerals that were discovered in a given year that continue to be known only from their type locality is found to decline exponentially over time. However, a few minerals remain known from only their type locality for long periods, including some that were first identified in the 19th Century. Conversely, other recently identified minerals have been subsequently recognised at locations spanning a wide geographic range such that the number of minerals with cosmopolitan distributions is found to increase exponentially over time. Taken together, these several quantitative representations of mineral distributions lend structure and refinement to qualitative and intuitive notions of the scarcity and abundance of Earth's many minerals.

Hexavalent chromium (Cr6+) is a toxic carcinogenic pollutant that might be released by the mining and processing of ultramafic rocks and nickel laterites and which requires permanent removal from the contaminated biosphere. Ultramafic material can also serve as a feedstock for the sequestration of CO2 resulting from the growth of new minerals, raising the intriguing proposition of integrated sequestration of both pollutants, CO2 and chromium, into magnesium carbonates. Such a synergistic process downstream of ore recovery and mineral processing could be an elegant proposition for more sustainable utilisation and management of the Earth's resources. We have therefore carried out an experimental and microanalytical study to investigate potentially suitable carbonate minerals. Uptake of chromium in carbonate phases was determined, followed by identification of the crystalline phases and characterisation of the local structural environment around the incorporated chromium centres. The results suggest that neither nesquehonite nor hydromagnesite have the structural capacity to incorporate Cr6+ or Cr3+ significantly at room temperature. We therefore propose that further research into this technology should focus on laboratory assessments of other phases, such as layered double hyroxides, that have a natural structural capacity to uptake both chromium and CO2.

Watanabeite from the Pefka epithermal deposit, northeastern Greece, was examined using single-crystal X-ray diffraction and electron microprobe analysis. The empirical formula of watanabeite is Cu3.93Fe0.10Ag0.01Pb0.23As1.55Sb0.19S4.99. This mineral is orthorhombic, space group Amm2, with unit-cell parameters a = 10.9601(5), b = 14.6498(8), c = 10.3001(5) Å, V = 1653.82(14) Å3 and Z = 8. The crystal structure was solved and refined to R1 = 0.0471 for 2108 unique reflections with Fo > 4σ(Fo) and 123 refined parameters. The crystal structure of watanabeite can be described as a three-dimensional framework of Cu-centred tetrahedra; cavities of the tetrahedral scaffolding host Cu6S and As2(Pb,Sb,As)2S7 clusters. On the basis of structural data, the formula of watanabeite could be written as [III]Cu3[IV]Cu5As3(Pb,Sb,As)S10 (Z = 4), considering the three independent three-fold Cu sites and the three independent tetrahedrally coordinated Cu sites as aggregated positions. The occurrence of Pb2+ in watanabeite is probably related to the substitution Cu+ + (As,Sb)3+ = 2Me2+, where Me = Pb, Fe, Zn and formally divalent Cu. The relationships with tetrahedrite-group minerals are discussed on the basis of the refined structural model, highlighting possible crystal chemical implications of such relationships.

Kristjánite, KNa2H(SO4)2, is a new mineral (IMA2022–131) found in a high-temperature fumarole on Fimmvörðuháls, Iceland. It is monoclinic, P21/n, a = 6.9625(1), b = 9.9953(1), c = 11.0928(2) (Å), β = 105.637(2)° and V = 743.40(2) Å3. Kristjánite forms colourless transparent crystals up to ~100 μm in size in compact aggregates with metathénardite, belomarinaite, aphthitalite, ivsite and an unknown mineral with tentative composition K2NaH(SO4)2, or grows in white globules of smaller grains on their surface. The eight strongest maxima in a powder X-ray diffraction diagram are [d, Å (Intensity)] 4.37 (59), 3.65 (32), 3.48 (78), 3.36 (100), 3.18 (76), 2.83 (43), 2.73 (38) and 2.405 (23). The mineral represents a novel crystal structure type. In it, K is coordinated by eight O atoms, and two symmetrically independent Na atoms by seven O atoms. Two symmetrically independent S atoms are in tetrahedral coordination by O atoms. A close to linear, very short hydrogen bond (2.44 Å), connects the two to a SO4–H–SO4 dimer. K and Na coordination polyhedra share vertices, edges and even faces forming with sulfate tetrahedra a tight structure with narrow [100] channels lined on two opposite sides by hydrogen bonds.

This study describes a new variety of chalcedony with a unique inhomogeneous bluish green hue, named aquaprase. It was discovered in Africa and is considered to be a valuable addition to the gem trade. A multi-methodological approach was used to examine its chemistry, mineralogy and microstructure, which were then compared to those of chrysoprase and agate, two of the most popular varieties of chalcedony. Optical microscopy revealed a complex microstructural heterogeneity in the different colour intensity areas/bands of aquaprase and agate, whereas chrysoprase exhibited a more homogeneous coexistence of micro- and cryptocrystalline quartz. High-resolution synchrotron XRD was essential for highlighting the complex assemblage of various types of α-quartz in aquaprase and agate (which differ in terms of crystal size and/or cell parameters). Micro-Raman spectroscopy revealed α-quartz and moganite in all three varieties of chalcedony and the presence of the nickel-bearing layered silicate mineral, willemseite, in chrysoprase, which is responsible for its green colouration. The chemical analysis displayed a homogeneous composition of agate, as well as high levels of nickel content in the chrysoprase variety. Aquaprase showed significant amounts (ppm by weight) of trace elements (Al, Mg, Na, K, Ca, Ti, U and Fe) characteristic of its formation environment, as well as high values of Cr, which are thought to be the cause of its bluish green colouration.

Valsassina (Lombardy, Northern Italy) is located in the Lombard Southern Alps and is characterised by the presence of a metamorphic basement, by a major late Variscan intrusive complex and by Carboniferous–Permian volcano-sedimentary cover units. These rocks host a pervasive system of inadequately studied mineralised veins. These veins are characterised by base metal (Pb, Zn, Cu and Fe) and complex polymetallic assemblages.

In this study, we have investigated the ore textures, mineral compositions of sulfides and sulfosalts (by EMPA–WDS and LA–ICP–MS analyses), and stable isotopes (C and O) in carbonate gangue minerals of various mineralised veins to determine the conditions of deposition of these ore deposits. Two different vein families can be recognised in Valsassina: NNW–SSE veins characterised by a complex polymetallic sulfide–sulfosalt assemblage, also with Ni–Co–Fe arsenides and other Ag–Bi-bearing minerals; and NE–SW veins with a simpler, base metal sulfide assemblage. The Ni–Co-bearing NNW–SSE veins have some distinctive features of the ‘five-element vein’ type deposits, with the Ni–Co–Fe arsenide ore stage pre-dating a sulfide-tetrahedrite-dominated ore stage. LA–ICP–MS data for pyrite and sphalerite, and stable isotopic compositions (C and O) of the carbonate gangue minerals, show no clear differences between the two families of veins, which are probably linked genetically. The isotopic compositions of the Valsassina vein carbonates are closely comparable with the signature of several major five-element ore districts. Preliminary temperature estimates for the Valsassina vein systems were based on the sphalerite composition, applying the GGIMFis geothermometer. The estimated temperatures for the sulfide-dominated ore stage post-dating the Ni–Co minerals precipitation range between 100 and 250°C. The crosscutting relationships, observed for all the veins with the host rocks, suggest a possible late to post Variscan (late Permian) age, making these vein systems comparable with other late–post Variscan polyphase hydrothermal events affecting large sectors of the Southern Alpine domain.

Plumboperloffite, PbMn2+2Fe3+2(PO4)3(OH)3, is a new mineral and member of the bjarebyite group from Wiperaminga Hill West Quarry, Boolcoomatta Reserve, Olary Province, South Australia, Australia. The mineral was found in a single cavity in triplite–barbosalite matrix associated with fluorapatite, phosphosiderite, natrodufrénite and fluorite. The mineral forms intergrowths of subparallel, thin tabular to bladed crystals. Individual crystals are up to 40 μm in length. Plumboperloffite is brownish orange in colour with a vitreous lustre. The mineral has brittle tenacity, an excellent cleavage on {100} and uneven fracture. The calculated density is 4.416 g/cm3. Plumboperloffite is biaxial (+), α = 1.87(1), β = 1.88(1) and γ = 1.89(1) as measured in white light. The measured 2V is 88(1)°. Dispersion is apparently strong, based on extinction colours and the orientation is Y = b. The pleochroism in shades of yellow brown is X < Z < Y. Electron microprobe analysis gave the empirical formula (based on 15 O apfu) (Pb0.92Ca0.04Ba0.01K0.01)Σ0.98(Mn2+1.84Fe2+0.13)Σ1.97(Fe3+1.97Al0.03)Σ2.00(P3.01O11.94)(OH)Σ3.06. Plumboperloffite is monoclinic, space group P21/m with a = 9.1765(18), b = 12.340(3), c = 5.0092(10) Å, β = 101.01(3)°, V = 556.8(2) Å3 and Z = 2. The crystal structure has been refined using X-ray single-crystal data to a final R1 = 0.0207 on the basis of 1417 reflections with Fo > 4σ(Fo). The mineral is isostructural with members of the bjarebyite-group minerals.

Heflikite, the first Sc-dominant epidote-supergroup mineral, was discovered in two occurrences. The holotype was found in a granitic pegmatite associated with rodingite-like calc-silicate rocks and metasomatised granitic bodies exposed in a serpentinite quarry at Jordanów Śląski near Sobótka, Lower Silesia, SW Poland. The cotype comes from the Heftetjern pegmatite, Tørdal region, Norway. The holotype is composed of (in wt.%): 35.69 SiO2, 0.22 TiO2, 21.98 Al2O3, 6.12 Sc2O3, 0.07 V2O3, 1.10 Fe2O3, 0.11 Y2O3, 1.55 La2O3, 4.05 Ce2O3, 0.31 Pr2O3, 1.53 Nd2O3, 0.40 Sm2O3, 0.11 EuO, 0.56 Gd2O3, 0.14 MnO, 3.56 FeO, 0.16 MgO, 19.16 CaO and 1.78 H2O(+)calc.; total 98.60. The cotype contains: 34.92 SiO2, 0.44 TiO2, 0.82 SnO2, 19.13 Al2O3, 4.79 Sc2O3, 1.96 Fe2O3, 2.55 La2O3, 7.39 Ce2O3, 0.48 Pr2O3, 0.67 Nd2O3, 0.12 EuO, 0.61 Gd2O3, 0.13 MnO, 5.97 FeO, 17.66 CaO and 1.73 H2O(+)calc.; total 99.37. The compositions correspond to the following empirical formulae: (Ca1.729Ce0.125La0.048Nd0.046Gd0.016Sm0.012Pr0.010Y0.005Eu2+0.003)Σ1.994[(Al2.182Sc0.449Fe3+0.070V3+0.005)Σ2.706(Fe2+0.251Mg0.020Mn0.010)Σ0.281Ti0.014]Σ3.001(Si3.006O11)O(OH) and (Ca1.644Ce0.235La0.082Nd0.021Gd0.018Pr0.015Eu2+0.004)Σ1.019[(Al1.958Sc0.362Fe3+0.128)Σ2.448(Fe2+0.434Mn0.009)Σ0.443(Ti0.029Sn0.029)Σ0.058]Σ2.949(Si3.033O11)O(OH), respectively, and to the ideal formula Ca2(Al2Sc)(Si2O7)(SiO4)O(OH). The crystal structure of the holotype was refined in the monoclinic system with an R1 index of 8.62%. The crystal-structure refinement indicates exclusively Si occupied T sites, Al occupied M1 and M2 sites, and a Ca occupied A1 site. The M3 site is filled predominantly by trivalent cations, mainly Sc3+, with divalent cations (mainly Fe2+) as minor occupants. The A2 site is filled mostly by Ca with minor amounts of rare earth elements (REE). The holotype heflikite crystallised from metasomatic fluids that infiltrated a contact between the granitic pegmatite and the surrounding rodingite-type calc-silicate rocks and serpentinites. The fluids that introduced Sc into the pegmatite could have been either hydrothermal or related to low-grade regional metamorphism that postdated the formation of the pegmatite. The cotype heflikite formed during the late-stage hydrothermal crystallisation of the Sc-enriched granitic pegmatite.

Arsenoústalečite is a new mineral discovered in a sample collected from the abandoned Ústaleč deposit near Horažďovice, SW Bohemia, Czech Republic. It occurs as rare anhedral grains, up to 40 μm in size, in a calcite gangue, associated with stibioústalečite, hakite-(Hg), berzelianite and uraninite. Arsenoústalečite is dark grey, with a metallic lustre. Mohs hardness is ca. 3½–4; calculated density is 5.730 g/cm3. In reflected light, arsenoústalečite is pale grey with a yellowish shade; it is isotropic. Internal reflections were not observed. Reflectance values for the four COM wavelengths in air [R (%) λ (nm)] are: 33.3 (470); 33.1 (546); 33.0 (589); and 32.9 (650). The empirical formula of arsenoústalečite is (Cu5.81Ag0.17)Σ5.98(Cu5.95Fe0.02Zn0.02Hg0.01)Σ6.00(As1.40Sb0.87Te1.73)Σ4.00(Se10.30S2.32)Σ12.61. The ideal formula is Cu12(As2Te2)Se13, which requires (in wt.%) Cu 34.76, As 6.83, Te 11.63, Se 46.78, total 100.00. Arsenoústalečite is cubic, I$\bar{4}$3m, with unit-cell parameters a = 10.6580(19) Å, V = 1210.7(6) Å3 and Z = 2. The strongest reflections of the calculated powder X-ray diffraction pattern [d, Å (I, %) hkl] are: 3.077 (100) 222, 2.848 (10) 321, 1.946 (12) 521, 1.884(52) 440 and 1.608(21) 622. According to the single-crystal X-ray diffraction data (R1 = 0.0285 on the basis of 334 unique reflections with Fo > 4σFo and 24 refined parameters), arsenoústalečite is isotypic with other tetrahedrite-group minerals. The crystal structure of co-existing stibioústalečite, with an empirical formula of (Cu5.69Ag0.07)Σ5.76(Cu5.80Zn0.13Fe0.06Hg0.01)Σ6.00(Sb1.82As0.42Te1.76)Σ4.00(Se9.52S3.10)Σ12.62 and unit-cell parameters a = 10.6975(16) Å, V = 1224.2(5) Å3 and Z = 2, was refined to R1 = 0.0191 on the basis of 267 unique reflections with Fo > 4σFo and 24 refined parameters. Structural relationships and crystal-chemistry of both members of the ústalečite series are discussed. Arsenoústalečite is named after its type locality, the Ústaleč deposit and its chemical composition. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2022-116).