This investigation investigates geologically old, ca. 370 Ma, metamict zirconolite from the Kovdor phoscorites and carbonatites in the Kola Alkaline Province. Mineral composition, crystallisation behaviour, and thermal expansion of the recrystallised samples were analysed using electron microprobe analysis, Raman spectroscopy, and in situ high-temperature powder X-ray diffraction (HTPXRD). The zirconolite crystals investigated are different in their morphology, internal texture, composition, alteration degree, and can be divided into four distinct groups. The zirconolite is a high Nb and Fe3+ variety (10.8–24.1 wt.% Nb2O5 and 7.9–9.0 wt.% Fe2O3), it is enriched in Th (up to 8.7 wt.% ThO2), Ta (up to 5.3 wt.% Ta2O5) and rare earth elements (up to 5.0 wt.% REE2O3). Raman spectroscopy confirmed that metamict zirconolite is anhydrous.

The recrystallisation process of the metamict zirconolite is complex, as detected by HTPXRD. A fluorite-type phase starts to crystallise at 420°C. The formation of a pyrochlore phase can be identified at 750°C. The major phases detected in the sample after the recrystallisation are: zirconolite-3T (53 wt.%), srilankite (25 wt.%), pyrochlore (15 wt.%), baddeleyite (5 wt.%) and zircon (3 wt.%). The average coefficients of thermal expansion (CTE) values in the temperature range 25–1200°C are as follows: ${{\bar \alpha }}$a = ${{\bar \alpha }}$b = ${{\bar \alpha }}$11 = ${{\bar \alpha }}$22 = 8.95·10–6 deg–1. Similarly, the thermal expansion along the c-axis yields a similar value: ${{\bar \alpha }}$a = ${{\bar \alpha }}$b = 8.93·10–6 deg–1, indicating an almost isotropic thermal expansion of zirconolite-3T. The lower CTE value compared to a pure synthetic zirconolite observed for zirconolite-3T might be attributed to the complex chemistry and polyphase nature of the material investigated.

Different two-dimensional structural units of layered silicate minerals have different chemical and reaction properties. Sulfuric acid solution mineral-leaching systems with pH of 2.0, 4.0 and 6.0 were constructed to investigate the differential dissolution properties of lizardite (1:1 type), chlorite and talc (2:1 type minerals) and the chemical kinetic mechanism of the mineral–water interface reaction. The results showed that the dissolution efficiency of Mg in lizardite is higher than that of chlorite and talc in acidic environments (pH of 2.0, 4.0 and 6.0). The dissolution efficiency of Mg in chlorite is greater than that of talc for acidic environments when pH is 2.0 and 4.0, but chlorite and talc have nearly identical Mg dissolution efficiencies at a pH of 6.0. This phenomenon is related to the defect site on the tetrahedral sheet of chlorite and is controlled by the change of the dissolution efficiency of Al. The dissolution rates of Mg and Si in lizardite, chlorite and talc decreased with the increase of reaction time in the acidic medium for pH = 2.0, 4.0 and 6.0, and there are two linear dissolution trends at different pH values. The dissolution efficiencies of Mg and Si in lizardite, chlorite and talc were simulated and predicted by establishing a logistic model. It was found that the maximum dissolution efficiency of 2:1 type minerals chlorite and talc are only 4.72% and 1.58%, which is much lower than that of 1:1 type lizardite. This research on the reaction mechanism and dissolution kinetics of lizardite, chlorite and talc not only helps to deepen the understanding of the mineral–water interface interaction, but also reveals the different rules for Mg, Si and Al dissolution in different types of trioctahedral mineral–water interface reactions, and provides a crystal chemical basis for the ion migration and action mechanism of minerals.

Laueite/stewartite epitaxy was studied using single-crystal diffraction applied to a composite crystal from Hagendorf-Süd, Bavaria. The orientation relationships between the crystals of the two minerals was facilitated by using a non-conventional B$\bar {1}$ space group setting for stewartite, giving unit cells with parallel axes and with as = 2al, bs = bl and cs = 2cl. Face indexing of the crystals of the two minerals confirmed the epitaxial relationship, with the {100} and {010} faces parallel. The plane of epitaxy is {010}. Refinement of laueite and stewartite datasets extracted from the composite-crystal data collection showed a significant decrease in the mean Mn-site bond distances in laueite, consistent with chemical analyses of the crystals that gave site compositions of Mn0.92Fe3+0.08 for stewartite and Mn0.66Mg0.17Fe3+0.17 for laueite. The epitaxial growth of laueite on {010} planes of stewartite appears to have been initiated by a change in solution chemistry. Possible paragenesis of the secondary phosphate minerals from primary triphylite is discussed.

The sulfide-free metasomatic rocks with chalcophile metals from the Nežilovo ore field, near Veles, Republic of North Macedonia belong to a rare kind of ore. The mineralogy and petrology of these rocks were studied in detail and can be considered as a standard description for ores of this type. A characteristic feature of Nežilovo-type ores is a wide variety of accessory oxide minerals containing chalcophile elements (Zn, Pb, Sb, Cu and As). The new nolanite-supergroup mineral zincorinmanite-(Zn), ideally (Fe3+2Zn)SbZnO7(OH), was discovered in the Nežilovo ore. The associated minerals are quartz, baryte, gahnite, Zn-bearing phlogopite, together with accessory hematite, almeidaite, a Pb-analogue of hydroxycalcioroméite and an insufficiently studied Sb-rich högbomite-supergroup mineral. Zincorinmanite-(Zn) forms lamellar to tabular subhedral single-crystal grains up to 0.5 mm across and up to 40 μm thick. The colour and streak are black and the lustre is submetallic. The new mineral is brittle, with the Mohs’ hardness of 6. No cleavage is observed. The fracture is uneven. The calculated density is 5.446 g·cm–3. In reflected light, zincorinmanite-(Zn) is light grey, no pleochroism is observed. The reflectance values (Rmin, %/Rmax, %/λ, nm) are: 12.6/13.7/470, 12.1/13.2/546, 11.8/12.8/589 and 11.5/12.2/650. The Raman spectrum shows bands corresponding to the O–H and Sb–O stretching vibrations and (Fe3+,M2+)–O–H bending modes. The chemical composition is (electron microprobe data, with iron divided into Fe2O3 and FeO based on the charge balance and H2O calculated from the structural data, wt.%): MgO 1.42, MnO 0.44, FeO 2.04, ZnO 22.55, Al2O3 1.95, Fe2O3 35.59, TiO2 1.51, Sb2O5 33.05, H2O 1.18, total 99.73. The empirical formula is [(Fe3+2.12Al0.18)(Zn0.32Mg0.16Fe2+0.13Mn0.03)Ti0.06]Σ3.00(Sb0.97Ti0.03)Σ1.00Zn1.00O7[(OH)0.61O0.39]Σ1.00. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.0191. Zincorinmanite-(Zn) is hexagonal, space group P63mc, a = 5.9720(1), c = 9.3578(1) Å and V = 289.031(8) Å3 (Z = 2). The new mineral is isostructural with other members of the nolanite group. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) – hkl] are: 5.176 (46) – 100; 3.473 (77) – 102; 2.989 (46) – 110; 2.674 (86) – 103; 2.520 (100) – 112; and 2.496 (42) – 201.

The Tertiary Sierra La Vasca intrusive complex of the Mexican Eastern Alkaline Province consists of diverse alkaline-to-peralkaline granitoids and syenites and is a rare example of silica oversaturated peralkaline magmatism characterized by eudialyte. The intrusion of these peralkaline rocks into Cretaceous carbonate country rocks resulted in the development of a unique cuspidine, Zr-bearing cuspidine, hiortdahlite and wollastonite exoskarn. This study is focussed on a eudialyte-bearing vein and accompanying banded exoskarn which illustrates the unusual skarn-forming metasomatic effects of Zr mobilization. The skarn consists of six mineralogically distinct zones: (1) a parental Nb-poor eudialyte-bearing quartz granitoid vein; (2) a region of eudialyte pseudomorphed by intergrown Zr-sorosilicates; (3) an andradite–cuspidine–hiortdahlite–wöhlerite zone; (4) a zone of skeletal-to-prismatic cuspidine plus wollastonite which is transitional to zone (5); a coarser grained and heterogeneous zone consisting of complex intergrowths of tabular and prismatic cuspidine–hiortdahlite solid solutions, wollastonite, fluorite, apatite and rare calcite; (6) a contact calcite marble lacking any metasomatic silicates, phosphates or fluorite. Skarn formation was the result of alteration of eudialyte and separation of Si-rich hydrothermal fluids with high F/H2O ratios from the parental Si-oversaturated peralkaline magma and subsequent infiltration of Si–Zr–REE–P-bearing fluids into the country rock carbonates. Zircon was probably transported as Zr-fluoride and chloride complexes and the acidic fluids reacted with calcite to form cuspidine–hiortdahlite solid solutions and wollastonite as the principal skarn minerals. All of the Si required to form this unique skarn assemblage was derived from the hydrothermal fluids as the country rocks do not contain Si-bearing minerals. Skarn formation is considered to have occurred at temperatures below 500°C.

Five discrete bismuth telluride compositions, characterised by high and variable degrees of Pb and Se substitutions, were observed at the Stall Lake VMS deposit in the Snow Lake area, Canada. The major cation substitutions are Pb (3.0 to 11.0 wt.%), Fe (0.2 to 1.4 wt.%), Cu (up to 0.9 wt.%) and Ag (up to 3.2 wt.%). The main anion substitution is Se (0.3 to 7.9 wt.%); S never exceeds 0.3 wt.%. These results were compared to a literature data compilation of all publicly available data for the pure bismuth tellurides tsumoite and tellurobismuthite, and the Pb-bearing rucklidgeite and kochkarite. On the basis of these new data and the literature compilation, a few generalisations about the substitutions in bismuth tellurides can be made. The major conclusion is that bismuth tellurides always contain at least some substitutional cations (Pb, Ag, Fe, Cu, Sb and Au), typically combining to ∼2 wt.% if Pb is excluded, and anions (mostly Se and some S, typically <1 wt.% combined). Another conclusion is that bismuth tellurides have highly variable compositions, which can be quite far from their theoretical ones, to the point of defining specific mineral varieties such as high-Pb tsumoite, low-Pb kochkarite, and high-Se rucklidgeite. Two high-Se bismuth telluride compositions were observed at Stall Lake (average Se ≈ 4.9 and ≈ 7.2 wt.%), which had never been documented before. This observation, in conjunction with the bismuth tellurides literature data, emphasises the high potential for both cation and anion substitutions in these minerals.

In the soil environment, divalent heavy metal ions often interact with trivalent metal ions to form hydrotalcite supergroup nanominerals (also known as natural layered double hydroxides, LDHs), effectively immobilising heavy metals within the minerals structure. Concurrently, these LDH minerals also show high surface reactivity and can adsorb surrounding heavy metal ions, thus they play a significant role in heavy metal pollution purification. However, the impact of the subsequent geochemical evolution of heavy-metal-containing LDHs on the migration and transformation of structural and surface-adsorbed heavy metals as well as its surface reactivity towards surrounding heavy metals remains unclear. Herein, Ni(II)Fe(III)-LDH and Co(II)Al(III)-LDH were taken as examples to reveal the influence of redox evolution on the immobilisation of structural and adsorbed heavy metals. The results of this work indicate that the oxidative–reductive alternating evolution of structural Ni, Fe and Co elements constrain the transformation of heavy metals, as well as their bioavailability greatly. The oxidative–reductive alternating evolution helped reduce the content of bioavailable heavy metals in exchangeable and carbonate-bounded states. It can also enhance the integration of heavy metals with the LDH structure and help transform heavy metals into residual states, thereby reducing their mobility and bioavailability. However, oxidative–reductive evolution significantly reduced the surface reactivity of LDHs, diminishing their interface locking ability for surrounding heavy metal ions. This research provides foundational data for assessing the long-term environmental performance of LDHs.

We present the first precise determination of the crystal structure for natural canfieldite from the Youqialang lead-silver mine in Nagqu, Tibet, China, using X-ray single-crystal and powder diffraction analysis. The structure was determined and refined to R1 = 0.0375 and wR2 = 0.0986 for a total of 14,743 reflections (2090 independent reflections) with a refined structure formula Ag7.94SnS6, compatible with the empirical formula Ag8.01Sn1.10S6 from electron microprobe analyses. Canfieldite is orthorhombic, with space group Pna21, a = 15.3079(4) Å, b = 7.5549(2) Å, c = 10.7038(3) Å, V = 1237.88(6) Å3 and Z = 4. The structure is composed of isolated SnS4 tetrahedra (average Sn–S bond length of 2.378 Å) arranged in a nearly equidistant manner in three-dimensions with Sn–Sn distances from 7.46 Å to 7.75 Å (the distance along the b-axis is equal to b) and the external S atoms outside the SSn4 tetrahedra are located at the centres surrounded respectively by 6 and 4 SnS4 tetrahedra. The Ag atoms are located in the space between SnS4 tetrahedra and external S atoms in tetrahedral, triangular and linear coordinations respectively with average Ag–S distances of 2.682 Å, 2.554 Å and 2.429 Å. The AgS4 tetrahedra, AgS3 triangles and linear AgS2 share corners and/or edges to form a framework which is corner-connected to SnS4 tetrahedra. Site splitting is present for some Ag atoms with the split distances from 0.26 Å to 0.42 Å. The orthorhombic Pna21 structure of natural canfieldite has similar arrangement of SnS4 tetrahedra and external S atoms to the high temperature cubic F$\bar 4$3m structure, but they are significantly different in the locations and bonding styles of Ag atoms with all the Ag atoms being disordered in the latter. The seven strongest lines of powder X-ray diffraction include [d in Å (I/I0) (h k l)]: 3.240 (45.1) (4 1 1); 3.230 (26.8) (2 0 3); 3.107 (28.1) (4 0 2); 3.084 (100) (0 2 2); 2.724 (49.2) (3 1 3); 2.462 (24) (4 1 3); and 1.895 (54.4) (4 2 4).

Ferrodimolybdenite with ideal formula FeMo3+2S4 (C2/c, a = 11.8249(8) Å, b = 6.5534(3) Å, c = 13.0052(10) Å, β = 114.474(9)°, V = 917.27(12) Å3 and Z = 8) was discovered in a differentiated sulfide nodule composed of troilite and pentlandite parts. The nodule was detected in the central zone of a diopside–anorthite–tridymite oval paralava body, ∼30 metres in diameter, within the pyrometamorphic Hatrurim Complex in Daba-Siwaqa, Jordan. Ferrodimolybdenite is the first trivalent molybdenum compound discovered in Nature. Its synthetic analogue crystallises in the C1c1 space group. Ferrodimolybdenite with the empirical formula (Fe2+0.99Cu2+0.07Ni2+0.04)Σ1.10Mo3+1.94(S2–3.98P3–0.02)Σ4.00 was identified in the troilite part of the differentiated sulfide nodule. The nodule contains inclusions of tetrataenite, nickelphosphide, molybdenite, galena and rudashevskyite. Ferrodimolybdenite forms platy crystals with dimensions ranging from 3×100 μm to 20×40 μm. The mineral exhibits a grey colour and a dark grey streak. It is opaque with a metallic lustre, and its Mohs hardness is ∼3. The cleavage observed in the mineral is perfect on {001}, good on {100} and poor on {010}. Its tenacity is sectile, and its fracture is smooth. The calculated density of 5.445 g·cm–3 was derived from the empirical formula and unit cell volume refined from single-crystal X-ray diffraction data. In reflected light, ferrodimolybdenite appears grey to light grey with a blueish tinge. It is anisotropic, with a reflectance in the range of 34–40%. The crystallisation of ferrodimolybdenite occurred in reduced conditions in monosulfide Fe(+Ni) melt at a temperature of 1000–1100°C and at low pressure.

Barium- and Ca-rich stronalsite [ideally SrNa2Al4Si4O16] occurs rarely as pseudomorphs, which are probably after nepheline, and is found in hydrothermally altered Sr-enriched leucocratic dykes or streaks hosted by mesocratic amphibole–pyroxene teschenite in the Silesian Unit (Flysch Belt of the Western Carpathians, Czech Republic). In addition to stronalsite, the pseudomorphs consist of slawsonite, celsian, biotite, muscovite, alkali feldspar, natrolite and thomsonite-Ca. The surrounding groundmass is rich in alkali feldspars and zeolites and sporadically also contains amphibole phenocrysts, chloritised biotite, fluorapatite and other accessory and/or secondary minerals. Both compositional types of stronalsite have identical Raman spectra. The Ba-rich stronalsite contains 0.55–0.83 apfu Sr, 0.12–0.37 apfu Ba, and <0.08 apfu Ca. In contrast, Ca-rich stronalsite contains 0.65–0.82 apfu Sr, 0.10–0.23 apfu Ca, and <0.06 apfu Ba. The substitution mechanisms by which Ca enters the structure of stronalsite could not be satisfactorily clarified from the available data; the best stoichiometric fit suggests for substitution of Sr, which should not be possible due to the different crystal structure of the Ca-analogue of stronalsite, lisetite [ideally CaNa2Al4Si4O16]. The Na contents range is 1.82–2.42 apfu and the K contents are consistently low (<0.09 apfu). The T site contains 3.91–4.26 apfu Si, 3.76–4.00 apfu Al and 0.00–0.11 apfu Fe3+. The main source of Sr was probably primary magmatic plagioclase that underwent hydrothermal alteration by post-magmatic high-temperature brines mixed with fluids of external origin. On the basis of previous research and paragenetic relationships, we estimate that stronalsite crystallised at T ∼250–320°C and P <100 MPa.

Parisite-(Nd) (IMA2024-013), ideally CaNd2(CO3)3F2, as the Nd-dominant analogue of parisite-(Ce), occurs in dolomitic marble in the Bayan Obo Fe–Nb–REE deposit, Inner Mongolia, China. It is associated with calcite, aegirine, magnetite, hematite, fluorite, riebeckite, bastnäsite-(Ce), baryte, aeschynite-(Ce), aeschynite-(Nd), monazite and parisite-(Ce). Parisite-(Nd) occurs as subhedral to anhedral irregular grains from 0.02 mm to 1 mm. Parisite-(Nd) is transparent, yellowish-brown colour, with pale yellow streak and displays vitreous to resinous lustre. Cleavage is distinct on pseudo-{001}; fracture is uneven, or conchoidal. The Mohs hardness is 4 to 5, and it is brittle. The calculated density of parisite-(Nd) is 4.357 g/cm3. Parisite-(Nd) is pseudo-uniaxial (+), ω = (1.679) and ε = (1.754). The empirical formula is (Ca0.945Fe0.058Sr0.015Ba0.007)Σ1.025(Nd0.967Ce0.529La0.191Pr0.137Gd0.070Sm0.029Th0.022Y0.016Nb0.011Ho0.003)Σ1.975(CO3)3F1.893OH0.023. The Raman spectra of parisite-(Nd) show strong and sharp peaks at 1113, 1090, 825, 635 and 1608 cm–1 and moderate to weak bands centred at 255, 392, 739, 924, 1183, 1228, 1296, 1640, 2247, 2924 and 3065 cm–1. Powder X-ray diffraction and TEM studies give the following results: monoclinic, space group: Cc (# 9), a = 12.3283(13) Å, b = 7.1185(4) Å, c = 28.4633(37) Å, β = 98.529(14)°, V = 2470.28(42) Å3 and Z = 12.

The environmental effects of nanoparticles have attracted widespread attention. The removal and recycling of nanoparticles are crucial for both environmental protection and resource reuse. However, current removal and recycling methods are not yet mature, and there is a need to explore inexpensive materials for the efficient removal and recycling of nanoparticles. This study investigates the effects of pyrite species, thermal modification temperature, pH and ionic strength on the adsorption of gold nanoparticles (AuNPs) by pyrite. The experimental results demonstrate that the adsorption rate of artificially thermally modified pyrite is slightly faster than that of naturally thermally modified pyrite. However, the concentration of Fe ions dissolved from the artificially thermally modified pyrite is higher. Natural pyrite, when thermally modified at 400°C and 500°C, adsorbs 100% of AuNPs within 10 min. The lower the acidity of the system, the faster the adsorption rate. Conversely, an increase in ionic strength decreases the adsorption rate. Artificially thermally modified pyrite primarily adsorbs AuNPs through electrostatic gravitational attraction, which is supplemented by a significant amount of chemisorption. After four recycling cycles, the adsorption and desorption rates of AuNPs using artificially thermally modified pyrite were 92.1% and 94.2%, respectively, indicating excellent adsorption and recovery performance. The results of this study provide a new method for the recycling of nanoparticles and an experimental basis for the further application of thermally modified pyrite in environmental treatments.

The new mineral manganonewberyite (IMA2024–004), Mn(PO3OH)(H2O)3, was found underground at the Cassagna mine, Liguria, Italy, where it is a secondary phase formed by the interaction of bat guano with Mn-rich rock. Manganonewberyite occurs with niahite, kutnohorite, sampleite and serrabrancaite on a tinzenite–quartz–braunite matrix. Crystals are prisms and blades, up to ∼0.15 mm long, elongated parallel to [001], flattened on {100} and exhibiting the forms {100}, {010} and {111}. Crystals are colourless and transparent, with vitreous lustre and white streak. The mineral is brittle with curved fracture. The Mohs hardness is ∼3. Cleavage is perfect on {010}. The density is 2.34(2) g·cm–3. Optically, manganonewberyite is biaxial (+) with α = 1.541(2), β = 1.547(2) and γ = 1.559(2) (white light). The 2V is 71.6(3)°. The optical orientation is X = a, Y = b and Z = c. The empirical formula is (Mn0.960Mg0.016Ca0.015)Σ0.991(H1.02P1.00O4)(H2O)3. Manganonewberyite is orthorhombic, space group Pbca, with cell parameters: a = 10.4273(6), b = 10.8755(8), c = 10.2126(4) Å, V = 1158.13(11) Å3 and Z = 8. The crystal structure (R1 = 2.79% for 892 I > 2σI reflections) is the same as that of newberyite with Mn in place of Mg.

The new ixiolite-group mineral nioboixiolite-(Fe3+), ideally (Nb0.5Fe3+0.5)O2, was discovered in nosean sanidinite of the Laach Lake (Laacher See) volcano, Eifel region, Rhineland-Palatinate, Germany. The associated minerals are sanidine, K-bearing albite, nosean, biotite, Nb-rich ilmenite, Ti-rich magnetite, hercynite, corundum, samarskite-(Y), ekebergite and columbite-(Fe). Nioboixiolite-(Fe3+) forms long prismatic to acicular crystals up to 0.03 × 0.06 × 1 mm and epitaxial intergrowths with ilmenite and intermediate members of the samarskite–ekebergite series. Both colour and streak are black and the lustre is submetallic. The new mineral is brittle, with the Vickers’ micro-indentation hardness of 499 kg mm–2 which corresponds to the Mohs’ hardness of 5. No cleavage is observed. The fracture is conchoidal. The calculated density is 5.033 g·cm–3. In reflected light, nioboixiolite-(Fe3+) is grey, no pleochroism is observed. The reflectance values (Rmin, %/Rmax, %/λ, nm) are: 14.7/16.4/470, 14.3/15.9/546, 14.1/15.7/589 and 14.0/15.8/650. The Raman spectrum shows bands corresponding to stretching vibrations of (Nb,Ti)–O–(Nb,Ti) and (Nb,Ti)–O–Mn2+ and the absence of bands of OH groups. The chemical composition is (electron microprobe data, wt.%): MgO 0.41, MnO 3.52, Al2O3 0.42, Cr2O3 0.75, Fe2O3 20.23, TiO2 22.26, ZrO2 0.76, Nb2O5 51.82, total 100.17. The empirical formula is (Mg0.04Mn2+0.20)Σ0.24(Al0.03Cr0.04Fe3+1.01)Σ1.08(Ti1.11Zr0.02)Σ1.13Nb1.55O8 (Z = 1). The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 3.586 (29) (110), 2.917 (100) (111), 2.503 (18) (002), 2.170 (18) (121), 1.738 (22) (130), 1.689 (26) (221). The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.0447. Nioboixiolite-(Fe3+) is orthorhombic with space group Pbcn, a = 4.6578(6), b = 5.6230(7), c = 5.0182(5) Å and V = 131.43(3) Å3. The new mineral is isostructural with other members of the ixiolite group.

Rubicline, RbAlSi3O8, is one of three known minerals containing essential rubidium and a geochemically significant member of the feldspar family. In the course of current work, RbAlGe3O8 (germanium analogue of rubicline) was grown hydrothermally via the formation of leucite-like RbAlGe2O6 as an intermediate phase. The crystal structure of RbAlGe3O8 was determined for the first time by direct methods from single crystal X-ray diffraction data and refined to R1 = 0.0528. It has monoclinic symmetry (space group C2/m, a = 9.1237(9), b = 13.5679(6), c = 7.4677(4) Å, β = 116.687(6)° and V = 825.95(11) Å3), with cell parameters typical for disordered feldspars. According to the high-temperature study, feldspar-like RbAlGe3O8 irreversibly transforms into the leucite-like phase RbAlGe2O6 at 1050°C. The thermal expansion of studied material displays a small negative change along the b axis. Its volume thermal expansion, fitted according to a linear model between 30 and 840°C (αV = 20.3(1) ×10–6 °C–1), is slightly higher than that of other feldspar-related compounds with essential rubidium.

Nancyrossite, ideally FeGeO6H5, is a new hydroxyperovskite from Tsumeb. It probably formed by the oxidation and partial dehydrogenation of stottite, FeGe(OH)6, with which it is associated intimately. The structure of nancyrossite has been determined in tetragonal space group P42/n: a = 7.37382(12) Å, c = 7.29704(19) Å, V = 396.764(16) Å3, Z = 4, R1(all) = 0.034, wR2(all) = 0.051 and GoF = 1.057. Empirical formulae of two crystals have almost end-member compositions, Fe3+1.01Zn0.03Ge0.98O6H5 and Fe3+1.01Zn0.04Ge0.98O6H5. Structure determination indicates that 88% of the Fe is ferric. The chemical formula proposed here for nancyrossite recognises that although H atoms form OH groups, writing the formula as FeGeO(OH)5 implies that one of the six oxygen atoms is very underbonded, with a bond-valence sum of only ∼1.2 valence units. As such, H in nancyrossite may have novel crystal chemistry. For example, the five H atoms may be distributed dynamically over the six O atoms, a phenomenon that would be averaged by X-ray diffraction, and so go undetected. Nancyrossite is the Ge-analogue of jeanbandyite. By analogy with nancyrossite, we propose revision of the ideal formula of jeanbandyite from FeSnO(OH)5 (Welch and Kampf, 2017) to FeSnO6H5.

A rare silver mineral, dervillite (ideally Ag2AsS2), has been found in specimens from the famous Jáchymov mining district, Czech Republic. It occurs as very rare long-prismatic crystals up to 0.4 mm across in association with proustite, bismuth and native silver in the thin arsenic veinlets within the Trojická vein (Svornost mine). Dervillite is monoclinic, space group Pc, with a = 9.6375(3), b = 12.9462(4), c = 6.8497(2) Å, β = 99.510(2)° and V = 842.88(2) Å3 (Z = 8). The new structure refinement, R1 = 2.94% for 18767 reflections with [I > 3σ(I)] and wR2 = 7.93% for all 20050 reflections, provided a better fit to the data compared to earlier studies, revealing that silver (8 symmetrically independent atomic sites), which adopts various coordinations (from quasi-linear to tetrahedral) in the structure of dervillite vibrates non-harmonically at room temperature. The Gram-Charlier development, describing the atomic displacement parameters of silver atoms, was used to model their non-harmonic behaviour. A discussion on the use of the approach to the data with limited quality is also provided.

The new mineral svornostite-(NH4) (IMA2024-068), (NH4)2Mg(UO2)2(SO4)4(H2O)8, was found in the Blue Lizard mine, San Juan County, Utah, USA, where it occurs as sprays and subparallel groups of yellow blades in a secondary assemblage with ammoniozippeite, blödite, boussingaultite, gypsum, hexahydrite, kröhnkite, plášilite and quartz. The streak is very pale yellow. Crystals are transparent with vitreous lustre. The tenacity is brittle, the Mohs hardness is ∼2½, the fracture is curved. The mineral is soluble in H2O and has a measured density of 3.06(2) g·cm–3. The mineral is optically biaxial (+) with α = 1.560(2), β = 1.564(2), γ = 1.589(2); 2V = 43(1)°; orientation: X = a, Y = b, Z = c; pleochroism: X colourless, Y yellow, Z yellow; X < Y ≈ Z. Electron microprobe analyses provided [(NH4)1.895Na0.065K0.040]Σ2.000(Mg0.755Mn0.252)Σ1.007(U0.996O2)2(S1.002O4)4(H1.998O)8. Svornostite-(NH4) is orthorhombic, Pmn21, a = 13.0259(9), b = 8.2909(4), c = 11.2589(4) Å, V = 1215.92(11) Å3 and Z = 2. The crystal structure (R1 = 0.0243 for 2222 I > 2σI reflections) contains uranyl-sulfate chains that are linked into sheets by MgO2(H2O)4 octahedra and 9- and 10-coordinated NH4+ groups. The sheet has the same topology as the sheets in several synthetic uranyl selenates. Svornostite-(NH4) is a member of the newly established svornostite group, which also includes svornostite-(K), oldsite-(K), rietveldite and zincorietveldite.

The Diely occurrence of metamorphosed As-rich manganese mineralisation is located in the Spišsko-gemerské rudohorie Mountains near the Poráč village and comprises Early Palaeozoic metamorphic rocks of the Gemeric Unit in the Western Carpathian region. Mineralisation is situated in the narrow tectonically delineated belt of Rakovec Group rocks consisting of mafic metavolcanic material generated during the back-arc submarine volcanic activity of the Early Ordovician–Silurian period. The Mn mineralisation is hosted in siliceous laminated lenses (metacherts) embedded in metabasalts and its tuffs. Manganese ore consists of quartz, braunite, rhodonite, nambulite, rhodochrosite, kutnohorite, OH-bearing garnets with dominant andradite composition, hematite, aegirine, aegirine–augite, ferri-ghoseite, ferri-winchite, baryte and pyrophanite. The mineralisation is cross-cut by a system of narrow younger veins composed dominantly of As-enriched minerals of the pyrosmalite group (schallerite, mcgillite and friedelite), tiragalloite, manganberzeliite, brandtite, sarkinite and svabite, associated with hematite, rhodochrosite, kutnohorite, baryte and quartz. Formation of manganese mineralisation at the Diely occurrence was caused by migration of seawater into the basaltic oceanic crust where increasing temperatures and acidity generated hydrothermal fluids enriched in manganese. The Mn-bearing hydrothermal fluids were enriched in Li, providing an additional substituent in the mineralisation. Following initial stages, the subsequent Variscan and Alpine tectonometamorphic events resulted in formation of three main mineralisation stages distinguishable by paragenetic relations and the mineral composition. Based on metamorphic association and amphibole geobarometric calculations, the peak metamorphic conditions reached was upper greenschist facies. The Diely occurrence near Poráč represents a unique metamorphosed manganese mineralisation with abundant arsenates and arsenosilicates previously unknown in the Western Carpathian region.

Two alluaudite-group minerals, badalovite, ideally NaNaMg(MgFe3+)(AsO4)3, and calciojohillerite, NaCaMgMg2(AsO4)3, have been identified on a specimen from the Monte Calvario quarry, Biancavilla, Etna volcanic complex, Sicily, Italy. For both species, this finding represents the second world occurrence. The studied sample was characterised using electron microprobe analysis, micro-Raman spectroscopy, and single-crystal X-ray diffraction. Badalovite occurs as vitreous to resinous aggregates of yellowish to brownish prismatic crystals, up to 0.5 mm in length, associated with tabular crystals of hematite, pseudobrookite and an amphibole-supergroup mineral. Badalovite is intimately intergrown with minor calciojohillerite. The chemical formulae of these two alluaudite-group members, recalculated on the basis of 12 O atoms per formula unit and assuming the occurrence of Fe3+, are (Na1.74(11)K0.01(1)Ca0.30(8))Ʃ2.05(Mg1.74(2)Mn0.27(2)Ca0.11(8)Zn0.03(1)Fe0.84(14)Al0.02(2))Ʃ3.01(As2.85(4)P0.11(3))Ʃ2.96O12 and (Na1.44(2)K0.01(1)Ca0.66(1))Ʃ2.11(Mg2.27(1)Mn0.28(1)Zn0.01(1)Fe0.48(2))Ʃ3.00(As2.79(3)P0.13(2))Ʃ2.92O12, respectively. Single-crystal X-ray diffraction data collected on badalovite gave the following unit-cell parameters a = 11.9760(5), b = 12.7857(5), c = 6.6650(3) Å, β = 112.689(2)°, V = 941.58(7) Å3, space group C2/c. Its crystal structure was refined to R1 = 0.0257 for 1711 unique reflections with Fo > 4σ(Fo) and 97 least-square parameters. The crystal chemical and spectroscopic data as well as the genesis of badalovite are discussed and a comparison with the Russian type material is reported.