Bornite (Cu5FeS4) and digenite (Cu9–xFexS5; x = 0.4) have closely related cubic structures and are known for their range of superstructures derived from metal vacancies leading to larger unit cells expressed as n × a, where a = ∼5.5 Å and n is an integer. Such polymorphs can form during cooling from higher temperature bornite (Bn)–digenite (Dg) 1a solid solution (ss). The alleged basket-weave textures in natural bornite are investigated using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) imaging and energy-dispersive X-ray spectrometry. These techniques, combined with crystal modelling and STEM simulations, are suitable for depicting changes in phases related to crystal-structural modularity as they collectively better reproduce atomic distributions in real space. Bornite associated with either chalcocite or chalcopyrite from the Olympic Dam Cu-U-Au-Ag deposit, South Australia has non-stoichiometric Cu/Fe ratios and displays nanoscale basket-weave textures between the main components Bn2a and anilite (Cu7S4); Dg1a is preserved throughout, albeit as a minor phase. Anilite is a derivative of digenite, whereby a = b = √2aDg and c = 2aDg. Two intermediate phases, Dg3a and Bn2a4a, are documented and an additional phase, Bn2a6a, is tentatively suggested to occur in Fe-rich nanodomains within Bn2a. Considering the epitaxial relationships between all phases, we infer that basket-weave textures record phase transitions via polymorphic transformations of parent Bn2a and Dg1a during cooling. Observed phase assemblages are thus linked to cooling of Bn–Dgss in the range 70–87 mol.% Bn along a Cu6.18Fe1.26S5 – Cu9.12Fe0.89S5 tie-line defined from measured compositions. We depict three associations: Bn2a + Dg1a, Bn2a4a + Dg3a, and Bn2a4a/Bn2a6a + anilite, formed during cooling. Polymorph associations like these are relevant for enrichment of critical/precious metals in copper ores because Bi, Pb, Ag, Te and, probably also Au, if dissolved in Bn–Dgss, could be incorporated into superstructures during Cu-Fe-sulfide phase transitions.

In this study, natural apatite containing fine-grained magnetite inclusions with well-developed shape-preferred orientation is investigated. These inclusions are aligned in trails parallel to the hexagonal prism facets and they are elongated along the c-axis of apatite. Electron probe microanalysis (EPMA) reveals a chemically homogeneous apatite, while energy-dispersive X-ray spectroscopy (EDS) and Raman spectroscopy identify these inclusions as magnetite. Carbonate-bearing inclusions, including calcite and gas-liquid inclusions with CO2, N2, and dissolved carbonate ions, are also observed. Calcite inclusions probably indicate early carbonatitic magma during apatite growth, whereas gas-liquid inclusions suggest late hydrothermal alteration. Optical microscopy reveals three shape-preferred orientation (SPO) groups of lamellar magnetite inclusions, each elongated parallel to <0001>Ap and to one of the three <11$\bar 2$0>Ap directions. Electron back-scatter diffraction (EBSD) analysis defines a consistent axial relationship of <0001>Ap//<110>Mag across all inclusions. Additionally, inclusions following the three SPO directions exhibit distinct but symmetrically related planar relationships, reflecting two specific crystallographic orientation relationships (CORs). COR-1: one of the {11$\bar 2$0}Ap planes parallel to one of the {411}Mag planes, and one of the {10$\bar 1$0}Ap planes parallel to one of the {211}Mag planes. This COR is expressed in direction 1 and 3 as two equivalent variants. COR-2: one of the {11$\bar 2$0}Ap planes parallel to one of the {211}Mag planes, and one of the {10$\bar 1$0}Ap planes parallel to one of the {411}Mag planes. These orientation patterns suggest variant selection during 2D interface-controlled nucleation, probably governed by the symmetry and surface geometry of the apatite host. The crystallographic relationships and the surface features of apatite suggest a secondary origin for magnetite, in which Fe was introduced through etch pits on the (0001) facet and nucleated along dislocations in crystal channels or pits. The hexagonal morphology of magnetite inclusions reflects the crystallographic control by apatite symmetry. We suggest that a fluid-induced dissolution-recrystallization process produces the hex-like morphologies of magnetite inclusions and facilitates their incorporation into the host. The necking-down of fluid inclusions further support this process.

The new mineral almagreraite (IMA2025-025), Cu2+ZnMn4+3O8, was found on the dump of the República Romana mine, Sierra Almagrera, Cuevas del Almanzora, Almería, Andalusia, Spain, where it occurs as tapering prisms or blades up to ∼0.4 mm in length, commonly forming subparallel to divergent aggregates. It is a secondary mineral associated intimately with well-crystallized blades of malachite on a matrix consisting of well-crystallized goethite and massive friable hematite. Crystals are black and opaque with submetallic lustre. The streak is dark grey with a brownish tint. The tenacity is brittle and the fracture is splintery. There are probably two cleavages (possibly {100} and {010}). The Mohs hardness is ∼5. The calculated density is 5.174 g·cm–3 based upon the empirical formula. In reflected light, the mineral is bluish grey in colour with moderate bireflectance and slightly bluish grey to a lighter bluish grey pleochroism. Electron probe microanalyses provided (Mn4+3.05Cu2+0.93Zn0.91Al0.05)Σ4.94O8. Almagreraite is orthorhombic, Pmn21, a = 5.7298(4), b = 4.9715(4), c = 9.3479(7) Å, V = 266.28(3) Å3 and Z = 2. In the crystal structure (R1 = 0.0297 for 423 I > 2σI reflections), Mn4+O6 octahedra share edges forming an octahedral sheet parallel to {001}. One in every four octahedra in the sheet is vacant, providing the sheet formula [Mn4+3O8]4–. Successive sheets are connected via bonds to Cu2+ and Zn2+ located in a layer between the sheets. The structure is similar to that of minerals of the nolanite supergroup and most notably the kamiokite group. Almagreraite is a member of a family of mixed-metal oxides with the generic formula M2Mn3O8, which are an important subject of study for the development of new materials.

The new mineral zanelliite, ideally PbCu9[AsO3.5(OH)0.5]2(AsO4)2(OH)9(H2O)3, was discovered at the Grosses Chalttal deposit, Mürtschenalp district, Glarus, Switzerland. It occurs as aggregates of {100} platy crystals, up to 0.05 mm in size, turquoise-green in colour. Lustre is vitreous. The calculated density is 4.425 g cm–3. The empirical formula, based on 28 O atoms per formula unit, is (Pb0.90Ca0.08)Σ0.98(Cu9.00Zn0.01)Σ9.01(As3.84Mo0.17)Σ4.01O15.17(OH)9.83(H2O)3. The occurrence of H2O was confirmed through micro-Raman spectroscopy and structural analysis. Zanelliite is monoclinic, space group C2/c, with unit-cell parameters a = 39.395(7), b = 5.5563(9), c = 10.5373(17) Å, β = 95.109(6)°, V = 2297.3(7) Å3 and Z = 4. The eight strongest reflections in the observed powder X-ray diffraction pattern are [d in Å (I)]: 19.7 (100), 4.86 (74), 4.48 (31), 4.28 (40), 3.777 (42), 2.964 (82), 2.708 (74), and 2.569 (37). The crystal structure of zanelliite was refined to R1 = 0.1215 for 2077 unique reflections with F > 4σ(F) and 125 refined parameters. Two different kinds of layers can be identified, i.e. a Cu–Pb–As heteropolyhedral layer, with composition [PbCu6As4O14(OH)6(H2O)], and a Cu layer, with formula [Cu3O(OH)4(H2O)2]. The crystal structure is composed of an alternating stacking of these two types of layers in a 1:1 ratio. Zanelliite is a supergene mineral whose origin is related to the oxidation of primary Cu ores. It is associated with brochantite, chrysocolla, heimite and parnauite. A second occurrence of zanelliite was reported from the Hochmättli deposit, Mürtschenalp district, Glarus, Switzerland. Zanelliite honours the mineral collector, mathematics and geography teacher Dr. Remo Zanelli (b. 1977) for his contributions to the knowledge of the secondary minerals of the ore deposits of the Glarus Alps. The mineral, its name, and its symbol (Znl) were approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2024-061).

Selenodantopaite is a new mineral species discovered in a sample collected from the mine dumps of the abandoned Princ Evžen deposit near Potůčky, the Krušné hory Mts., Czech Republic. Selenodantopaite occurs as anhedral grains, up to 100 μm in size, in a quartz gangue with abundant coffinitized uraninite, chalcopyrite and pyrite; it is also associated with bohdanowiczite, unnamed selenide (Bi,Ag)3(Se,S,Te)4, minerals of the galena–clausthalite solid solution, sphalerite and tennantite-(Fe). Selenodantopaite is dark grey, with metallic lustre. Mohs hardness is ca. ∼3½, calculated density is 7.403 g.cm–3. In reflected light, selenodantopaite is white to light grey; bireflectance and pleochroism are weak, anisotropy is distinct with light bluish white – light purplish brown rotation tints. Internal reflections were not observed. Reflectance values for the four COM wavelengths of selenodantopaite in air [Rmax, Rmin (%) (λ in nm)] are: 48.3, 44.9 (470); 48.8, 45.3 (546); 48.4, 45.1 (589); and 47.7, 44.6 (650). The empirical formulae, based on electron-microprobe analyses, are Cu0.24(4)Ag5.09(7)Fe0.17(5)Pb0.51(4)Bi12.32(21)Se15.11(21)S6.89(21) and Cu0.05(3)Ag5.23(11)Fe0.06(4)Pb0.62(12)Bi12.38(13)Se14.77(16)S7.23(16) for Cu-bearing and Cu-poor variety, respectively. The ideal formula is Ag5Bi13Se22 (Z = 1), which requires (in wt.%) Ag 10.80, Bi 54.41, and Se 34.79, total 100.00. Selenodantopaite is monoclinic, C2/m, with unit-cell parameters a = 13.670(4), b = 4.1400(11), c = 19.282(6) Å, β = 106.385(11)° and V = 1046.9(5) Å3. According to the single-crystal X-ray diffraction data (R1 = 0.0625), the crystal structure of selenodantopaite is isotypic with that of dantopaite and it is composed by two kinds of slabs, parallel to (001), i.e. a PbS-like thick slab and a thin slab, following the classical structural scheme of pavonite homologues. Selenodantopaite is named in accord with its composition and its relationship with dantopaite. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (2023-092)

The new mineral, babunaite-(Nd) NdAsO4, was discovered in metasomatic rocks of the Mixed Series near the Nežilovo village in Northern Macedonia. These rocks are characterised by an unusual occurrence of Pb-Zn oxide ore mineralisation. This area forms part of the high-grade metamorphic region of the Upper Precambrian Pelagonian massif. Babunaite-(Nd) is an accessory mineral in pink schists, which mainly consists of Mn-bearing muscovite and quartz, with minor braunite. Accessory minerals are hematite, gahnite, almeidaite, långbanite, zircon, piemontite and piemontite-(Pb), nežilovite, Sb-bearing rutile, fluorapatite, As-bearing fluorapatite, gasparite-(La), chernovite-(Y), arsenoflorencite-(La). Babunaite-(Nd) forms single crystals measuring up to 70 μm in size. The transparent crystals exhibit an adamantine lustre and a pale-yellow colour. The microhardness of babunaite-(Nd) is VHN25 = 578(21) kg/mm2, equivalent to a hardness of 5 on the Mohs scale. The mineral is brittle and does not exhibit cleavage. The mean composition of the holotype crystal is as follows: (Nd3+0.39Ca0.14Th0.09Pr3+0.08La0.07Sm3+0.06Y0.06Gd0.05Ce3+0.02Eu3+0.01)Σ0.97(As5+0.95W6+0.05V5+0.01)Σ1.02O4. The calculated density is 5.918 g·cm–3. Babunaite-(Nd), with the general crystal chemical formula ABO4, has a scheelite-type structure and crystallises in the tetragonal I41/a space group: a = 5.1363(2) Å, c = 11.5764(8) Å, V = 305.41(3) Å3 and Z = 4. The main bands at 190, 348, 440 and 833 cm–1 are distinguished in the Raman spectrum of babunaite-(Nd). A synthetic analogue of babunaite-(Nd) is known, which forms under high-pressure and high-temperature conditions of 11 GPa and 1100–1300°C. The genesis of the Mixed Series rocks occurred under metamorphic conditions approaching the parameters of the kyanite–graphite subfacies, at which gasparite-(Nd) with the monazite structure should form. The formation of babunaite-(Nd) is associated with the stabilisation of its structure by a tungsten (W) impurity. It is the first arsenate phase containing rare earth elements (REE) in the scheelite group.

Pseudosection modelling of a relict garnet-core in Palaeoproterozoic rocks from the Gridino area in the southern Belomorian belt of Karelia reveals peak-pressure eclogite-facies conditions of 610–650°C, 18–20 kbar for two retro-eclogite samples and 610–665°C, 23–26 kbar for a rare Mg-rich biotite-orthopyroxene eclogite, suggesting low initial metamorphic field gradients of 6.6–10°C/km. This confirms an earlier finding in Karelia and, considering other Palaeoproterozoic eclogite occurrences worldwide, that ‘cold’ subduction conditions, characteristic of modern-style subduction, occurred during the Palaeoproterozoic, ∼2 Ga ago, for the first time in Earth history. However, compositions of most other phases in the retro-eclogite were reset by diffusion, deformation and recrystallisation during subsequent pressure release and heating to variable degrees, a reason for earlier overestimations of temperatures. By contrast, peak-pressure conditions for a biotite paragneiss (640–740°C, 15–18 kbar) that occurs close to the biotite-orthopyroxene eclogite locality already show an early resetting of its initial assemblage. High-pressure granulite-facies peak-temperature conditions of the retro-eclogite at 712± 5°C, 9–12 kbar (along a field gradient of 20°C/km) were determined by Zr-in-rutile thermometry and quartz-in-garnet elastic barometry. These conditions were dated by a Rb/Sr mineral isochron for the biotite-orthopyroxene eclogite at 1830±20 Ma for the first time. Using existing ages for the peak-pressure conditions, possible slow overall exhumation rates of <0.9 mm/y between eclogite and the granulite-facies stages could be determined that are compatible with erosion as the main exhumation mechanism. The peak-temperature conditions were possibly established by thermal relaxation during early exhumation. However, a younger Rb/Sr mineral isochron for the biotite paragneiss indicates a characteristic Sr-isotopic disequilibrium distribution caused by diffusion during slow cooling between ∼1800 and 1750 Ma during later exhumation.

Chlorite plays an essential role in transporting water into the deep Earth. This study investigates the high-pressure behaviour of clinochlore up to ∼20 GPa at room temperature, using synchrotron X-ray diffraction and infrared spectroscopy. We identified a polytypic phase transition (from IIb-2 to IIa-1) at ∼9 GPa and a structural distortion at ∼12 GPa. The polytypic phase transition at ∼9 GPa is characterised by a significant reorganization of interlayer hydrogen bonding, transitioning to states of weakly bonded or non-hydrogen-bonded hydroxyl groups. The phase transition showed reversibility during the experiment. The structural distortion near 12 GPa indicates adjustments in the compression mechanism related to the hydroxyl groups across both the brucite-like and 2:1 sheets. The unit-cell volume of the low-pressure IIb-2 phase was fitted to the second-order Birch-Murnaghan equation of state, and the resulting parameters are V0 = 710.9(3) Å3 and K0 = 83.4(8) GPa. Our results exhibit a marked deviation from prior experimental findings, potentially attributable to the presence of Fe2+ cation incorporation in the natural chlorite investigated in this work. This study emphasises the complexity of the hydroxyl group in response to pressure in layered-structure silicates.

The new mineral stibiosegnitite, ideally Pb(Fe3+2.5Sb5+0.5)(AsO4)2(OH)6, was found in the Phosphatno-Arsenatnaya vein, at the 245 m level of the Southern open pit operating at the Murzinskoe gold deposit, Altai Krai, Western Siberia, Russia. In the holotype specimen, stibiosegnitite forms pseudo-cuboctahedral crystals up to 0.02 mm grouped in compact aggregates forming a thick crust 8 × 6 cm in area on quartz-limonite matrix in association with malachite and pseudomalachite. The new mineral is olive-green, transparent to translucent with a greenish-yellow streak. It is brittle with uneven fracture. Its lustre varies from adamantine in crystals to dull earthy in aggregates. Cleavage is distinct on {001}. Mohs’ hardness is ∼4. Dcalc. = 4.760 g·cm–3. The infrared, Raman and X-ray photoelectron spectroscopy data are given. Stibiosegnitite is optically uniaxial (–) and nonpleochroic with ω = 1.935(10) and ε = 1.920(10). Chemical data (wt.%, electron microprobe; all Sb is considered as Sb5+ based on XPS data; H2O calculated from H content determined by CHNS-analysis): CuO 0.91, PbO 29.31, Al2O3 2.78, Fe2O3 20.42, SiO2 0.22, P2O5 2.89, As2O5 25.01, Sb2O5 11.61, H2O 7.13, total 100.28. The empirical formula calculated on the basis of 14 O atoms per formula unit is Pb1.00(Fe3+1.95Al0.42Cu0.09Sb5+0.55)Σ3.01(As1.66P0.31Si0.03)Σ2.00O7.97(OH)6.03. Stibiosegnitite is trigonal, space group $R \bar{3} m$, with a = 7.3462(7), c = 17.115(2) Å, V = 799.90(14) Å3 and Z = 3. The new mineral has an alunite-type structure. The latter was refined to R1 = 0.0485 for 241 independent reflections with I > 2σ(I). Stibiosegnitite is a new member of the dussertite group within the alunite supergroup. The name of the mineral reflects its close relation to segnitite from which it can be obtained via the coupled heterovalent substitutions Fe3+0.5 + (AsO3OH)2– → Sb5+0.5 + (AsO4)3–.

Pyrochlores, general formula A2–mB2X6–wY1–n and cubic Fd$\bar 3$m (Z = 8) symmetry, are oxide and fluoride minerals with a peculiar structure consisting of a framework of corner-linked BX6 octahedra. The framework is arranged such that it forms tunnels parallel to the [110] direction, which are occupied by the A and Y sites at the centre (or in slightly displaced neighbouring positions). Atoms hosted at the tunnel sites are particularly susceptible to ion-exchange processes, especially when these sites are occupied by highly mobile species (e.g. water) or are partially vacant; this is the case for hydropyrochlore and hydrokenopyrochlore from the Lueshe carbonatite, both extensively altered and hydrated due to intense weathering. Their ion-exchange properties are remarkable, making them suitable candidates for Tl+ sequestration from aqueous matrices. This study focuses on the kinetics of the ion-exchange reaction involving monovalent thallium, incorporated by single crystals through progressively longer imbibition experiments in Tl-rich solutions. Structural (single-crystal X-ray diffraction) and chemical (electron microprobe analysis) investigations carried out before and after each imbibition experiment showed that Tl+ is incorporated in the structure at both tunnel sites and tends to order preferentially at A with increasing A:B occupancy ratios. The entry of Tl+ seems to be accompanied by a progressive shift in colour of the crystals (from colourless to dark brown). The incorporation process is relatively quick, as it approaches a saturation limit (~70–75% of the A site occupancy) in, cumulatively, 450 minutes of treatment; longer imbibition experiments (930 minutes) only led to a slight redistribution of electrons among the tunnel sites.

Nioboixiolite-(Fe2+), with ideal formula (Nb2/3Fe2+1/3)O2, occurs in granitic pegmatite adjacent to rodingitized calc-silicate rocks and serpentinite in a Jordanów Śląski quarry, Lower Silesia, Poland. It forms euhedral prismatic crystals up to 50 μm, scattered in lenticular aggregates of Ti,Nb-bearing minerals (Nb-rutile, ilmenite, titanite, Ca,Pb-hydropyrochlore) between quartz and albite. The mineral is opaque black, non-fluorescent, with a black streak, submetallic lustre, ∼5 Mohs hardness, brittle uneven-to-conchoidal fracture, and no cleavage. Density is 5.374 g·cm–3 (empirical formula, refined unit-cell volume). In reflected light, it appears grey (slightly darker than Nb,Ta-rutile), without pleochroism; reflectance 16.8(5)–18.4(5)%, very weak bireflectance, weak anisotropy, no internal reflections. The empirical structural formula, normalized to 2 oxygen atoms per formula unit (apfu) and expressed as groups of cations of the same valence, is as follows: [(Nb0.509Ta0.048)Σ0.557(Fe2+0.144Mn0.061Mg0.006)Σ0.211(Fe3+0.064Sc0.058)Σ0.121(Ti0.102Zr0.004Sn0.002)Σ0.108□0.003]Σ1.000O2.000 where □ = vacancy. It is dominated by pentavalent and divalent cations, among which Nb5+ and Fe2+ predominate. The crystal structure of nioboixiolite-(Fe2+) was refined in the orthorhombic system (space group Pbcn) to R1 = 2.22%. Nioboixiolite-(Fe2+) crystallises in an α-PbO2 structure, which is typical for all minerals from the ixiolite group, in which all cations, surrounded octahedrally by oxygen atoms, are disordered at one M site. The holotype crystal has the following unit-cell parameters: a = 4.7368(2) Å, b = 5.7155(2) Å, c = 5.0831(2) Å, V = 137.616(9) Å3 (a: b: c = 0.8288: 1: 0.8894). Raman spectra show four groups of peaks attributed to lattice modes, bending modes, and symmetric and asymmetric stretching modes, with the strongest asymmetric 872(1) cm–1 band originating from the stretching vibrations of the shortest Ti–O, Nb–O and Ta–O bonds, modified by vibrations of larger Fe3+–O, Fe2+–O and Mn2+–O bonds.

Anningite-(Ce) ideally (Ca0.5Ce4+0.5)(VO4), was found within a phosphate coprolite from the sand-dominated sediments of the Gara Samani Formation, Algeria. As a tetragonal anhydrous vanadate, this mineral is classified in the xenotime group. It occurs in rock cavities and forms small (typically up to 100 μm in length) sheaf-like aggregates composed of crystals 30–40 μm in length and ∼7 μm in diameter. Anningite-(Ce) crystals are green with a vitreous lustre. No cleavage is observed and the fracture is uneven or conchoidal. Its empirical formula, calculated on the basis of 4 oxygen atoms, can be written as (Ca0.52Ce4+0.47Y3+0.01)Σ1.00[(VO4)0.88(PO4)0.05(SO4)0.06(SiO4)0.01]Σ1.00. The calculated density is 3.887 g/cm3. Anningite-(Ce) is tetragonal with space group I41/amd and unit-cell parameters a = 7.1500(4) Å, c = 6.3343(7) Å, and V = 323.82(5) Å3. Anningite-(Ce) is isostructural with wakefieldite-(Ce).

Carbonatite is one of the major archives of rare earth elements (REEs), and in some cases, its formation is linked to the deep subduction of carbonated ocean crust and REE-rich sediments. The formation conditions of hydroxyl REE carbonate, [Sm(CO3)OH] or ‘hydroxylbastnäsite-(Sm)’ (it is not presently an IMA-approved mineral), in a subduction zone were simulated at 3 GPa and 1073 K. The crystal structure of Sm(CO3)OH was determined using single crystal X-ray diffraction (XRD), which shows the crystal to be hexagonal with cell parameters a = b = 12.2143 (7) Å, c = 9.8393 (6) Å, V = 1271.26 (17) Å3, and space group $P\bar 6$. The high-pressure properties of synthesized Sm(CO3)OH were investigated using in-situ synchrotron powder XRD and Raman spectroscopy at pressures up to 20.9 and 20.6 GPa at ambient temperature, respectively. Additionally, the structural stability of Sm(CO3)OH under pressure and temperature conditions up to 5.9 GPa and 473 K was also investigated using Raman spectroscopy. A third-order Birch–Murnaghan equation of state fitted to the ambient temperature and high-pressure data points yielded K0 = 76 (11) GPa with K0ʹ = 13 (2), and K0 = 127 (2) GPa if K0ʹ is constrained to a value of 4. Analysis of axial compressible moduli shows an apparent compression anisotropy of Sm(CO3)OH: Ka = 215 (5) GPa and Kc = 265 (5) GPa. Raman spectra of the synthesized quenchable crystal of Sm(CO3)OH displayed no detectable phase transition at the pressure range from ambient to 20.6 GPa, and no noticeable phase transition when the temperature and pressure were increased from ambient conditions to 473 K and 5.9 GPa, respectively. These results suggest that the [Sm(CO3)OH] phase may play a potential role as a conveyor for the migration of rare earth elements (REE), carbon (C) and water (-OH) to the deep Earth during plate subduction.

Kopernikite, K(Ti7Cr3+)O16 – a new mineral belonging to the priderite group with a hollandite-type structure, was discovered within a graphite–troilite nodule in the Morasko iron meteorite of the IAB-MG type. This meteorite fell in the territory of modern-day Poland around 5000 years ago. Kopernikite is confined to the external graphite zone of the nodule and intergrows with fluorapatite. The kopernikite structure was refined (I4/m, a = 10.0955(5) Å, c = 2.9534(2) Å, V = 301.01(4) Å3 and Z =1) for the grains with the composition (K1.12Ba0.23Ca0.03Na0.03)Σ1.42(Ti4+6.48Cr3+1.46Fe2+0.01 Al0.01)Σ7.96O16 based on 375 unique reflections to R1 value of 0.018. The colour of kopernikite changes from dark green in massive grains to yellow–green in thin grains, and the streak is light green. The mineral has a vitreous lustre and a hardness of ∼5.5 on the Mohs scale, as calculated on the basis of microhardness VHN25 = 646(17) kg/mm2. The Raman spectrum of kopernikite is similar to that of priderite. Kopernikite crystallised from drops of phosphate melt simultaneously with fluorapatite at a temperature of 1000°C, due to the local enrichment of the melt with K, Ba, Ti and Cr. The increased amount of tunnel cations in the kopernikite structure (∼1.4–1.5 apfu), as calculated from microprobe analyses, exceeds the theoretically possible value of 1.33 apfu for minerals of the priderite group. This increase can be attributed to formation of kopernikite under the increased pressure, as well as artefacts that appear when the mineral composition is measured using a microprobe analyser.

The petrographic and geochemical characterisation of the diagenetic calcite and dolomite associated with carbonate-hosted ore deposits can contribute to a better understanding of mineralisation mechanisms. The lower Carnian Breno Formation and Calcare Metallifero Bergamasco in the Dossena area (Gorno mining district, Lombardy Basin, Southern Alps) are two shallow marine carbonate lithostratigraphic units hosting Alpine-type Pb-Zn-F-Ba ores. Several interpretations have been proposed for the genesis of mineralisation in these Triassic carbonates: syngenetic from submarine exhalations linked to the Ladinian–Carnian volcanism; or Alpine-type syngenetic to epigenetic in burial settings by hydrothermal fluids, during Early–Middle Jurassic rifting. Recent studies propose that ores formed in shallow burial settings (tens to few hundreds of metres), precipitated from hydrothermal fluids related to Triassic magmatism, prior to the Early Jurassic rifting.

Petrographic analysis, δ18O data, REEYN normalised patterns, calculated element ratios and lanthanum, cerium and europium normalised anomalies suggest precipitation of the saddle dolomite and calcite cements, filling-fractures preceding and post-dating the mineralisation, from low temperature (<200°C) hydrothermal fluids. The geochemistry of these fluids was influenced by seawater and burial basinal brines. REEYN patterns and Y/Ho ratios suggest the interaction of these fluids with Permian and Ladinian–Carnian siliciclastic and volcaniclastic deposits and/or with the Variscan metamorphic basement, which are possible sources for metals.

The identified paragenesis supports a hydrothermal epigenetic origin for the mineralisation, at burial depths not shallower than 300 m. In fact, pre-mineralisation fractures filled by saddle dolomite and calcite cements cross-cut voids occluded by burial sparite cements and stylolites in an already lithified host rock, affected by burial compaction and pressure solution.

These conclusions may contribute to the understanding of other global occurrences of carbonate-hosted Pb-Zn mineralisation, providing new insights into complex dolomite and calcite paragenesis preceding and following the ore formation.

Crystal-chemical features of high-calcium and hypercalcium eudialyte-group minerals (EGMs) from a carbonatite-related rock of the Tamazeght peralkaline complex, High Atlas Mountains, Morocco were studied using electron probe microanalysis, single-crystal X-ray structure analysis, infrared and Raman spectroscopy. The major components of the host rock are calcite, fluorite and EGMs; aegirine–augite is present in subordinate amounts. The specific features of the studied EGMs are chemical heterogeneity, a complex zoning, reaction zones around calcite and apatite inclusions, Na- and Cl-deficiency, high contents of Ca, Mn, REE, Nb, carbonate and H-bearing groups, positive correlation between Nb and Mn and negative correlations between the pairs Fe–Mn and Zr–Mn. These features confirm previous assumptions about the role of infiltration of carbonatite fluid rich in Ca, Mn, REE, Nb, CO2 and H2O and a depletion of Cl in the remaining fluid after the crystallization of sodalite at the expense of nepheline in the formation of carbonatite-related rocks of the Tamazeght complex. The crystal structure of a single-crystal fragment extracted from the Nb-rich zone refined to R1 = 0.0335 has shown a high degree of ordering of Na, REE and H3O+ and the dominance of Fe3+ at the M2 site with five-fold coordination. The composition of EGMs from the reaction zones around calcite and apatite inclusions corresponds to Mn-dominant (with Mn > Fe at the M2 site) analogue of feklichevite with the simplified formula Ca3(Na,K)9(H3O)3Ca6Zr3(Mn2+,Fe3+,Zr)3NbSi(Si24O72)(OH,H2O)5(F,Cl)2/3(CO3)1/3.

As-rich florencite-(La) occurs as microscopic inclusions within pink–orange euclase and quartz from auriferous hydrothermal veins in Abaíra, Bahia State, Brazil. Electron probe microanalysis indicates a predominance of phosphate over arsenate at the tetrahedral site. Single-crystal X-ray diffraction reveals slight unit-cell expansion in the As-rich variety. Raman spectroscopy detects both phosphate- and arsenate-related vibrational modes, along with weak OH-stretching and diffuse bands attributable to hydrogen-bonded species, indicating mainly structural hydroxyl with possible contributions from weakly bound H2O. The mineral probably formed during a late hydrothermal stage involving progressive REE enrichment and oxidising, acidic fluid conditions. These findings emphasise the structural sensitivity of florencite-(La) to tetrahedral-site substitutions and hydrogen bonding, and its potential as a sensitive tracer of REE-enriched hydrothermal systems.

Mineral Cup is an annual global volunteer-run competition to determine the most popular mineral, decided by public voting and played out mainly on social media. Over nine years of Mineral Cup, nine distinct minerals or mineral groups have been crowned champion, in chronological order: olivine, garnet, ice, magnetite, quetzalcoatlite, fluorite, zircon, rhodochrosite and kyanite. Participants in Mineral Cup can vote for minerals for any reason, ranging from scientific and often esoteric to aesthetic. Factors influencing voting include name or nickname, colour, striking appearance, utility, unusual characteristics, cultural impact, and fun facts. Mineral Cup has a global reach, with over 30,000 voters a year in 2018–2025 encompassing voters from over 100 countries per year. The popular knockout format of Mineral Cup could also be used in a wider range of geoscience competitions, and in late 2025 the first such instance of a spin-off competition (Ore Cup) was held. In the context of declining enrolments in geoscience degrees, we discuss Mineral Cup as a potential tool to promote the joy of mineralogy widely, including to audiences that may otherwise have limited or no exposure to geoscience. Finally, we provide an outline of future directions of Mineral Cup, the reach of which as an entity is currently limited by volunteer time and availability in much the same way as professional society activities are limited by the availability of their members.

Eleven chert samples from various geographical and geological locations and ages were heat treated, with two of the samples also undergoing in situ X-ray diffraction (XRD) during heat treatment. Characterisation was performed using X-ray fluorescence (XRF), XRD and Raman spectroscopy. The results indicated that the presence of moganite in cherts is independent of whether they are quartzitic or cristobalitic/tridymitic. After heating, cherts cannot be differentiated into these two types using XRD, as all the samples might contain quartz, cristobalite and tridymite. Heat treatment induced transformations in both siliceous and non-siliceous phases, forming new crystalline phases. The observed transformations at 1000°C agree with the literature data. The combination of XRD and Raman spectroscopy is crucial for comprehensive chert analysis, with Raman methods detecting lower concentrations and textural variations than XRD. A correlation exists between chert type (quartzitic or cristobalitic/tridymitic), i.e. mineralogy and age, but not between elemental composition and age. In situ XRD during heating shows distinct crystalline transformations. These transformations can affect significantly the properties of the cherts and has implications for conservation and provenance studies of archaeological tools. The analytical tools used to characterise the mineralogy of cherts are a fast and efficient alternative to conventional petrographic microscopy, especially in the case of heat-treated cherts.