A nomenclature and classification scheme for wöhlerite-group minerals has been established. The general formula of minerals belonging to this group is given by X8(Si2O7)2W4, where X = Na+, Ca2+, Mn2+, Ti4+, Zr4+ and Nb5+; and W = F– and O2–. In addition, they may incorporate significant amounts of Mg2+, Fe2+, Y3+ and REE3+, where REE are the lanthanides. The main structural feature of these minerals is the four-columns-wide octahedral walls, which are interconnected through corner sharing and via the disilicate groups. The wöhlerite-group minerals crystallise in different unit-cell settings and symmetries, depending on the cationic ordering in the octahedral walls and the relative position of the disilicate groups. Different combinations of X and W constituents should be regarded as separate mineral species. In the case of coupled heterovalent substitutions at different crystallographic sites, it is advised to use the site-total charge approach to determine the correct end-member composition. Due to their structural and chemical features, wöhlerite-group minerals can easily form crystals with several micro domains, showing different crystal structures and chemical compositions. In addition, the crystallisation of polytypes is relatively common, although they should not be regarded as distinct mineral species. To date, ten minerals belonging to the wöhlerite group are considered as valid species: baghdadite, burpalite, cuspidine, hiortdahlite, janhaugite, låvenite, moxuanxueite, niocalite, normandite and wöhlerite. Låvenite and normandite are isostructural and are respectively the Zr and Ti end-members of a solid-solution series. Marianoite is discredited, as it is corresponds to wöhlerite. The ideal formula of hiortdahlite is revised as Na2Ca4(Ca0.5Zr0.5)Zr(Si2O7)2OF3, with one cationic site characterised by a valency-imposed double site-occupancy. These changes have been approved by the IMA–CNMNC (Proposal 20–D).

Garpenbergite is a new mineral (IMA2020-099) from the Garpenberg Norra mine, Hedemora, Dalarna, Sweden. It occurs with carlfrancisite and minor stibarsen, paradocrasite and filipstadite in a fractured skarn matrix of granular jacobsite, alleghanyite, kutnohorite and dolomite. Crystals are short-prismatic, up to 1.5 mm in length. They have a blackish to greyish brown colour, and are lustrous semi-opaque, with brown streak. Garpenbergite is brittle, with an uneven to subconchoidal fracture. Cleavage is distinct on {010}. Hardness ≈ 5 (Mohs) and VHN100 = 650(40). Dcalc = 4.47(1) g⋅cm−3, overall ncalc = 1.85. Maximum specular reflectance values (%) obtained are 9.2 (470 nm), 9.1 (546 nm), 9.0 (589 nm) and 8.9 (650 nm). The empirical chemical formula of garpenbergite, based on electron microprobe data, is (Mn2+3.97Mg1.48Mn3+0.26Zn0.29)Σ6.00(As0.89Fe3+0.04Mn3+0.06Si0.01)Σ1.00(Sb0.98Fe0.02)Σ1O10[(OH)1.99Cl0.01]Σ2.00. The five strongest Bragg peaks in the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are 3.05 (30) (002), 2.665 (100) (161), 2.616 (40) (301), 2.586 (25) (251) and 1.545 (45) (462). The orthorhombic unit-cell dimensions (in Å) are a = 8.6790(9), b = 18.9057(19) and c = 6.1066(6), with V = 1001.99(18) Å3 for Z = 4. The crystal structure was refined from single-crystal X-ray diffraction data in the space-group Ibmm to R1 = 3.7% for 957 reflections. Garpenbergite, ideally Mn6As5+Sb5+O10(OH)2, is isostructural with manganostibite, Mn7AsSbO12, but possesses a cation vacancy (□) at an octahedrally coordinated structural site; the two minerals are thus related by the exchange Mn2+ + 2O2– → □ + 2(OH)–. The presence of hydroxyl groups is supported by vibration bands at 3647 and 3622 cm−1 in the Raman spectrum of garpenbergite and by bond-valence considerations.

The crystal chemistry and crystal structure of the rare earth element phosphates, monazite-(Ce), Ce(PO4), and xenotime-(Y), Y(PO4), as well as the arsenates, gasparite-(Ce), Ce(AsO4), and chernovite-(Y), Y(AsO4), from the hydrothermal quartz-bearing fissures, related to pegmatites overprinted by amphibolite facies, cropping out at Mt. Cervandone, Western Alps, Piedmont, Italy, have been investigated by means of electron microprobe analysis in wavelength dispersion mode and single-crystal X-ray diffraction. The chemical data reveal the occurrence of a full solid solution among the isostructural chernovite-(Y) and xenotime-(Y) with tetragonal symmetry, whereas a wide miscibility gap is observed for the isostructural gasparite-(Ce) and monazite-(Ce) of Mt. Cervandone, with monoclinic symmetry. A significant chemical heterogeneity has been observed for several investigated samples, especially related to the Th content, which is locally enriched in ThSiO4 grains. The analysis of the refined structural models demonstrates the significant control played by the composition of the tetrahedrally-coordinated (As,P)-bearing sites on the bulk unit-cell volume, and on the size and shape of the (REE)-coordination polyhedra.

Princivalleite, Na(Mn2Al)Al6(Si6O18)(BO3)3(OH)3O, is a new mineral (IMA2020-056) of the tourmaline supergroup. It occurs in the Veddasca Valley, Luino area, Varese, Lombardy, Italy (46°03’30.74’’N, 8°48’24.47’’E) at the centre of a narrow (2–3 cm wide) vertical pegmatitic vein, a few metres long, crosscutting a lens of flaser gneiss. Crystals are subhedral (up to 10 mm in size), azure with a vitreous lustre, conchoidal fracture and white streak. Princivalleite has a Mohs hardness of ~7, a calculated density of 3.168 g/cm3 and is uniaxial (–). Princivalleite has trigonal symmetry, space group R3m, a = 15.9155(2) Å, c = 7.11660(10) Å, V = 1561.15(4) Å3 and Z = 3. The crystal structure was refined to R1 = 1.36% using 1758 unique reflections collected with MoKα X-ray intensity data. Crystal-chemical analysis resulted in the empirical crystal-chemical formula

X(Na0.54Ca0.11□0.35)Σ1.00Y(Al1.82Mn2+0.84Fe2+0.19Zn0.07Li0.08)Σ3.00Z(Al5.85Fe2+0.13Mg0.02)Σ6.00[T(Si5.60Al0.40)Σ6.00O18](BO3)3O(3)[(OH)2.71O0.29]Σ3.00O(1)[O0.66F0.22(OH)0.12]Σ1.00 which recast in its ordered form for classification purposes is:

X(Na0.54Ca0.11□0.35)Σ1.00Y(Al1.67Mn2+0.84Fe2+0.32Zn0.07Mg0.02Li0.08)Σ3.00ZAl6.00[T(Si5.60Al0.40)Σ6.00O18](BO3)3V[(OH)2.71O0.29]Σ3.00W[O0.66F0.22(OH)0.12]Σ1.00.

Princivalleite is an oxy-species belonging to the alkali group of the tourmaline supergroup. The closest end-member compositions of valid tourmaline species are those of oxy-schorl and darrellhenryite, to which princivalleite is related by the substitutions Mn2+ ↔ Fe2+ and Mn2+ ↔ 0.5Al3+ + 0.5Li+, respectively. Princivalleite from Veddasca Valley is a geochemical anomaly, originated in a B-rich and peraluminous anatectic pegmatitic melt formed in situ, poor in Fe and characterised by reducing conditions in the late-stage metamorphic fluids derived by the flaser gneiss. The Mn-enrichment in this new tourmaline is due to absence of other minerals competing for Mn such as garnet.

Stibiogoldfieldite, Cu12(Sb2Te2)S13, was approved as a new mineral species from the Mohawk mine, Goldfield mining district, Esmeralda County, Nevada, USA. It occurs as metallic anhedral grains, dark grey in colour. It is associated with quartz, pyrite and an Ag–Bi–(S,Se) phase (holotype material) and with quartz, pyrite, calaverite, bismuthinite, bohdanowiczite, and the Ag–Bi–(S,Se) phase (cotype material). In reflected light, stibiogoldfieldite is isotropic, grey in colour, with indistinct brownish shade. Reflectance data in air [R (%)] are: 31.1 at 470 nm, 30.9 at 546 nm, 30.8 at 589 nm and 31.0 at 650 nm. Electron microprobe analysis for holotype material gave (in wt.% – average of 60 spot analyses): Cu 45.03(60), Ag 0.26(7), Fe 0.02(3), Zn 0.13(15), Sn 0.02(4), Pb 0.05(6), Sb 8.02(62), As 2.80(65), Bi 2.77(87), Te 15.15(1.24), S 24.50(32), Se 0.52(11), total 99.27(69). On the basis of (As + Sb + Te + Bi) = 4 atoms per formula unit (apfu), the empirical formula of stibiogoldfieldite is (Cu12.05Ag0.04Zn0.03Fe0.01)Σ12.13(Sb1.12As0.63Bi0.23Te2.02)Σ4.00(S12.99Se0.11)Σ13.10. Chemical data on an additional sample from the same locality (cotype material) gave the following results (in wt.% – average of 181 spot analyses): Cu 43.84(63), Ag 0.21(7), Sb 5.92(78), As 2.63(45), Te 20.07(1.19), S 25.13(53), Se 0.97(35), total 99.47(66). On the basis of (As + Sb + Te + Bi) = 4 apfu, the empirical formula of cotype material is (Cu11.30Ag0.03)Σ11.33(Sb0.80As0.57Bi0.06Te2.57)Σ4.00(S12.83Se0.20)Σ13.03. Stibiogoldfieldite is cubic, I$\overline 4$3m, with unit-cell parameters a = 10.3466(17) Å, V = 1107.6(5) Å3 and Z = 2 (holotype). Unit-cell parameters for the cotype sample are a = 10.3035(2) Å and V = 1093.83(7) Å3. The crystal structure of holotype stibiogoldfieldite was refined by single-crystal X-ray diffraction data to a final R1 = 0.032 on the basis of 285 reflections with Fo > 4σ(Fo) and 20 refined parameters. Stibiogoldfieldite is isotypic with other members of the tetrahedrite group.

The diffusivity and diffusion mechanisms of hydrogen together with with deuterium and lithium, parallel to the c axis of quartz, were investigated experimentally at 800°C, 0.1 GPa with the activity of H2O or 2H2O ≈ 1 [2H is used throughout this work to describe deuterium rather than D, to avoid confusion with the diffusion coefficient, D]. The pH was set using mixtures of H2O (or 2H2O) and HCl. Three types of experiment were conducted: (1) H-in/Li-out; (2) 2H-in/H-out; and (3) 2H-in/H + Li out, using three different natural quartz crystals as starting materials. Profiles of H, 2H and Li were measured using Fourier-transform infrared (FTIR) spectroscopy and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). H, 2H and Li are charge-compensated by Al3+ replacing Si4+, or by excess O2–. The total atomic concentration of monovalent cations appears to remain constant over the duration of the experiments. The resulting diffusion profiles are different for the three experimental designs and three starting materials, and some show complex shapes inconsistent with simple diffusion. A multi-site diffusion–reaction model is developed, with the theory based on previous models that have been derived mainly on the basis of conductivity measurements. In these models, the monovalent cations move away from their charge-balancing ion then diffuse rapidly to another site. The mobility of the monovalent cations is described by both a diffusion coefficient and an equilibrium constant that enables dissociation of the immobile charge-balanced defects. This model can describe complex step-shaped profiles formed in H-in/Li-out experiments, profiles with local maxima ('humped’ profiles) in 2H-in/H + Li out experiments, and error function-shaped profiles in 2H-in/H-out and previously published Li-in/H-out experiments. Our data provide support for models previously proposed for quartz. Studies of the lengths and forms of diffusion profiles from such experiments provide a useful complement to assertions from conductivity experiments.

The response of garnet and zircon to prograde amphibolite-facies metamorphism in late Proterozoic mica schists from the Scottish Highlands has been investigated. Spatial analysis of zircon populations using scanning electron microscopy was undertaken in Dalradian Schists that have undergone a sequence of prograde garnet growth and localised breakdown reactions involving coupled dissolution–reprecipitation. Fluid availability and matrix permeability strongly control this metamorphic response and different generations of garnet contain radically different populations of metamorphic micro-zircon and associated changes in the detrital zircon population. Micro-zircon abundance increases during garnet growth, whereas that of detrital zircon decreases. The mineralogy of the matrix influences zircon abundance in porphyroblast phases, where garnet overgrows a micaceous matrix zircon-rich garnet forms and where it overgrows a quartzofeldspathic matrix the result is zircon-poor garnet. Following garnet growth, micro-zircon abundance decreases at each stage of the prograde reaction history, with sillimanite-zone schists containing the lowest abundance, suggesting micro-zircons are texturally less stable at staurolite- and sillimanite-grade metamorphism. Micro-zircons are distributed evenly across host minerals in the matrix, with the exception of retrograde chlorite where micro-zircons are absent due to fluids removing Zr before new zircon can precipitate. There is an overall decrease in the mode of zircon at each stage of the reaction history, indicating that zircon is a highly reactive phase during amphibolite-facies metamorphism and is very sensitive to individual prograde and retrograde reactions.

Hydroplumboelsmoreite (IMA21-C), (Pb,□)2(W,Fe3+)2O6(H2O), is a redefined elsmoreite-group mineral in the pyrochlore supergroup. It was found in a ‘jixianite’ cotype specimen provided by Mr. Liu Jianchang, who first found ‘jixianite’ in 1979 in the Jizhou District, Tianjin City, China. The mineral occurs as yellow to reddish brown aggregates, together with raspite and another elsmoreite-group mineral under study. Hydroplumboelsmoreite occurs in cryptocrystalline form and occasionally in octahedral microcrystalline form (under 20 μm in size). The crystals are colourless and translucent with a white streak, and the lustre is adamantine to greasy. Hydroplumboelsmoreite is isotropic, with a calculated refractive index of 2.29, a Mohs hardness of ~4½–5, and a calculated density of 7.47 g⋅cm−3. The strongest five powder X-ray diffraction lines [d in Å(I)(hkl)] are 6.070(28)(111), 3.012(100)(222), 2.603(32)(004), 1.836(35)(044) and 1.568(30)(226). The crystal structure was refined to R1 = 0.0459 using 80 unique reflections collected with MoKα radiation, and the results show that the mineral is cubic, space group Fd$\bar{3}$m, with a = 10.3377(5) Å, V = 1104.77(16) Å3 and Z = 8. Electron microprobe analyses and crystal structure refinement were used to determine the empirical formula: (Pb1.05Sr0.05Ce3+0.07Na0.01□0.82)Σ2.00(W1.32Fe3+0.67Zr0.01)Σ2.00O6[(H2O)0.43O0.19□0.38]Σ1.00. The mineral was named hydroplumboelsmoreite based on the predominance of Pb, W, and molecular H2O in the A, B and Y sites, respectively.

A new occurrence of kintoreite, ideally PbFe3(PO4)(PO3OH)(OH)6, is described from the Tripi mine, Alì, Peloritani Mountains, northeastern Sicily, Italy. Kintoreite occurs as yellow equant crystals, up to 0.05 mm in size, on quartz, associated with another alunite-supergroup mineral currently under study. The studied grains of kintoreite are chemically zoned, showing the occurrence of two distinct domains. Electron microprobe analyses gave (in wt.%): SO3 5.47(27), P2O5 17.55(14), Al2O3 7.81(35), Fe2O3 23.81(44), PbO 35.11(41), H2Ocalc 9.93, total 99.68 (darker domains) and SO3 6.03(5), P2O5 16.66(23), Al2O3 4.22(2), Fe2O3 27.31(6), PbO 33.78(22), H2Ocalc 10.25, total 98.25 (brighter domains). On the basis of 14 O atoms per formula unit (apfu) and (P+S) = 2 apfu, the darker and brighter domains have chemical formula Pb1.00(Fe3+1.89Al0.97)Σ2.86[P1.57S0.43O7.43(OH)0.57][(OH)5.58(H2O)0.42]Σ6.00 and Pb0.98(Fe3+2.21Al0.53)Σ2.74[P1.51S0.49O7.49(OH)0.51][(OH)5.18(H2O)0.82]Σ6.00, respectively. Single-crystal X-ray diffraction was performed on a grain extracted from the same sample. Unit-cell parameters are a = 7.2191(10), c = 16.834(3) Å, V = 759.8(3) Å3 and Z = 3; space group R$\bar{3}$m. The crystal structure was refined on the basis of 226 unique reflections with Fo > 4σ(Fo) and 31 least-square parameters to R1 = 0.0415. Kintoreite is isotypic with other alunite-supergroup minerals. Micro-Raman spectroscopy suggests the possible occurrence of H2O groups, supporting the possible protonation of (OH) groups as a charge-balance mechanism in this mineral. Kintoreite may play an environmental role in the Alì area, where previous authors detected high concentrations of potentially toxic elements in soils.

Gallium (Ga) and germanium (Ge) are technologically important critical elements. Lead blast furnace slags from Tsumeb, Namibia, comprise over two million metric tons of material that contains high levels of Ga (135–156 ppm) and Ge (128–441 ppm) in addition to significant Zn concentrations (up to 11 wt.%) and represent a potential resource for these elements. A combination of mineralogical and chemical methods (PXRD, FEG-SEM-EPMA and LA-ICP-MS) indicated different partitioning of Ga and Ge within the individual slag phases. Gallium is predominantly bound in small euhedral crystals of Zn–Fe–Al spinels (<10 μm in size), exhibiting concentrations in the range of 480–1370 ppm (up to 0.004 atoms per formula unit, apfu). Concentrations of Ga in other phases (e.g. melilite) are systematically below 90 ppm. The principal host of Ge is the silicate glass and, to a lesser extent, silicates (melilite and olivine group phases). Concentrations of Ge in glass attained a concentration of 470 ppm (EPMA), but the LA-ICP-MS analysis of glass matrix containing submicrometre spinel crystallites indicated that average Ge levels vary in the range of 113–394 ppm. In the potential extraction of Ga and Ge, the results indicate that ultrafine milling is needed to liberate the Ga- and Ge-hosting phases prior to metallurgical processing of the slag.

Fractionation factors for the isotopes of O, H, S, or Cu (as appropriate) were determined for the minerals brochantite [Cu4(SO4)(OH)6], libethenite [Cu2(PO4)(OH)] and olivenite [Cu2(AsO4)(OH)] and corresponding aqueous solutions at temperatures between 30 and 70°C. All samples used for this determination were synthetic and the degree of fractionation was expressed as 1000 ln α = (A × 106/T2) + B, where A and B are empirical parameters. A few natural libethenite samples from its type locality Ľubietová-Podlipa were also analysed and compared to the prediction based on the isotopic composition of meteoric water and our fractionation factors. The hydrogen fractionation factors agreed with the prediction well, whereas those for oxygen did not. A possible explanation is the disequilibrium of aqueous phosphate (and also arsenate) species and the solution in our experiments or the interaction of meteoric fluids with the isotopically heavy (in terms of oxygen) country rocks. Because the effects of isotopic disequilibrium in our experiments cannot be ruled out, the oxygen fractionation factors should be used with caution. The determined fractionation factors can be used as an isotope geothermometer, given that it can be proven that the phases of interest precipitated from the same fluid in equilibrium. Libethenite is predicted to have slightly lower δ65Cu values than its parental solution, but brochantite slightly higher δ65Cu values than its parental solution. Simple forward models, simulating neutralisation or reduction of mine drainage, show that precipitation of these minerals and removal of the co-existing fluid, could cause isotopic variations (in δ65Cu) on the order of 1‰ or more.

Hydrothermally synthesised K2ZnSi5O12 has a polymerised framework structure with the same topology as leucite (KAlSi2O6, tetragonal I41/a), which has two tetrahedrally coordinated Al3+ cations replaced by Zn2+ and Si4+. At 293 K it has a cation-ordered framework P21/c monoclinic structure with lattice parameters a = 13.1773(2) Å, b = 13.6106(2) Å, c = 13.0248(2) Å and β = 91.6981(9)°. This structure is isostructural with K2MgSi5O12, the first cation-ordered leucite analogue characterised. With increasing temperature, the P21/c structure transforms reversibly to cation-ordered framework orthorhombic Pbca. This transition takes place over the temperature range 848−863 K where both phases coexist; there is an ~1.2% increase in unit cell volume between 843 K (P21/c) and 868 K (Pbca), characteristic of a first-order, displacive, ferroelastic phase transition. Spontaneous strain analysis defines the symmetry- and non-symmetry related changes and shows that the mechanism is weakly first order; the two-phase region is consistent with the mechanism being a strain-related martensitic transition.

Tennantite-(Hg), Cu6(Cu4Hg2)As4S13, was approved as a new mineral species (IMA2020-063) from the Lengenbach quarry, Imfeld, Binn Valley, Canton Valais, Switzerland. It was identified as an aggregate of black metallic tetrahedral crystals, less than 0.1 mm in size, intimately associated with sinnerite, and grown on realgar. In reflected light, tennantite-(Hg) is isotropic, grey in colour, with creamy tints. Minimum and maximum reflectance data for COM wavelengths in air are [λ (nm): R (%)]: 470: 29.1; 546: 29.1; 589: 28.5; 650: 27.7. Electron microprobe analysis gave (in wt.% – average of 7 spot analyses): Cu 32.57(42), Ag 6.38(19), Tl 0.29(14), Zn 0.04(5), Hg 17.94(2.27), Pb 0.70(51), As 17.83(61), Sb 0.34(8), S 24.10(41), total 100.19(1.04). The empirical formula of the sample studied, recalculated on the basis of ΣMe = 16 atoms per formula unit, is (Cu4.69Ag1.04Tl0.03)Σ5.76(Cu4.35Hg1.58Pb0.06Zn0.01)Σ6.00(As4.20Sb0.05)Σ4.25S13.26. Tennantite-(Hg) is cubic, I$\overline 4$3m, with a = 10.455(7) Å, V = 1143(2) Å3 and Z = 2. The crystal structure of tennantite-(Hg) has been refined by single-crystal X-ray diffraction data to a final R1 = 0.0897 on the basis of 214 unique reflections with Fo > 4σ(Fo) and 22 refined parameters. Tennantite-(Hg) is isotypic with other members of the tetrahedrite group. Mercury is hosted at the tetrahedrally coordinated M(1) site, in accord with the relatively long M(1)–S(1) distance (2.389 Å), similar to that observed in tetrahedrite-(Hg). Minor Ag is located at the triangularly-coordinated and split M(2) site. Other occurrences of tennantite-(Hg) are briefly reviewed and the Lengenbach finding is described within the framework of previous knowledge about the Hg mineralogy at this locality.

We report on the crystal structures of three novel synthetic SrM-arsenates (M = Ni and Fe3+), isostructural or structurally related to the minerals from tsumcorite, carminite and brackebuschite groups. They were synthesised under mild hydrothermal conditions and further characterised using single-crystal X-ray diffraction (SXRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and Raman spectroscopy. SXRD and SEM-EDS yielded formulae: (I) SrNi2(AsO4)2⋅2H2O, (II) Sr1.4Fe3+1.6(AsO4)2(OH)1.6 and (III) SrFe3+(AsO4)(AsO3OH). All three structures are built up of slightly distorted MO6 octahedra and AsO4 tetrahedra that are linked by Sr2+ with different coordination geometries and hydrogen bonds. I represent a basic structure type typical for tsumcorite-group minerals (space group C2/m) while II has a new intermediate structure between carminite, PbFe3+2(AsO4)2(OH)2 and arsenbrackebuschite, Pb2Fe3+(AsO4)2(OH) (s.g. Pm). III is triclinic and adopts a new structure-type (s.g. P$\bar{1}$). The structure of I is built up of infinite linear edge-sharing NiO4(OH2)2 octahedral chains, extending along [010] and linked by AsO4 tetrahedra, SrO8 polyhedra and hydrogen bonds. The structure of II is characterised by the carminite-like FeO4(OH)2 octahedral chains and Edshammar-polyhedral chains, which involves SrO11 coordination polyhedra similar to that of PbO11 in arsenbrackebuschite. Both chains in II are aligned parallel to the b axis of the monoclinic unit cell and connected together by the arsenate AsO4 tetrahedra, SrO8 polyhedra and the hydrogen-bonding network. The compound III has a new type of crystal structure based on the unusual corrugated octahedral–tetrahedral-quadruple chains. These are made up of a central double-sided chain linked to two single-sided chains into a quadruple chain extended along the a axis. The chains in III are built up of FeO6 octahedra and AsO4 tetrahedra further linked to each other by shared vertices. The quadruple chains are interconnected by additional AsO4 tetrahedra forming a heteropolyhedral 3D open framework. Strontium atoms are situated in the two channels. The structural connections to related minerals and inorganic compounds are discussed.

A nomenclature scheme has been set up for the nordite supergroup of minerals, which have the general formula A2BXYZT6O17 and where A = Na; B = Na, Ca; X = Sr, Ca, Ba; Y = REE, Sr; Z = Zn, Fe, Mn, Mg and T = Si. The nordite supergroup includes nordite-(La), nordite-(Ce), ferronordite-(La), ferronordite-(Ce) and manganonordite-(Ce), as well as meieranite which is considered as an unassigned member of the nordite supergroup. In the known nordite-group minerals the Y site is occupied by rare earth elements (REE), while in meieranite the Y site is occupied by Sr. The dominant element on the tetrahedral Z site determines the prefix used in the mineral name. New rootnames must be given to species with a different dominant element on the A, B or X sites. Nordite supergroup minerals are orthorhombic, although nordite-group minerals and meieranite crystallise in the Pcca and P21nb space groups, respectively. The proposed nomenclature scheme for the nordite supergroup has been approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA). In addition, new chemical and structural investigations were performed on nordite-(Ce) from Illutalik (Igdlutalik), South Greenland, leading to the first crystal structure refinement for nordite-(Ce).

Copper-sulfides within carbonatites and phoscorites of the Phalaborwa Igneous Complex, South Africa, have been investigated since the middle of the 20th Century. However, aspects of ore formation have remained unclear. This study examines the mechanisms involved in Cu-sulfide mineralisation by micro-focus X-ray computed tomography as applied to sulfide-rich drill core samples. Several texturally distinct assemblages of magmatic sulfides can be identified, including: (1) <500 μm rounded bornite and chalcopyrite grains disseminated within the gangue; (2) elongated mm-scale assemblages of chalcopyrite and bornite; and (3) mm-to-cm thick chalcopyrite cumulates. Chalcopyrite veins were also observed, as well as late-stage valleriite, documenting late-stage fluid circulation within the pipe, and alteration of magmatic and hydrothermal sulfides along fractures within the gangue, respectively. The results of micro-focus X-ray computed tomography indicate that magmatic sulfides are sub-vertically aligned. Spatial variability of the sulfide assemblages suggests that textural changes within sulfide layers reflect fluctuating magma flow rate during emplacement of carbonatite–phoscorite magmas, through coalescence or breakup of sulfide liquid droplets during ascent. Modal sulfide abundances, especially for disseminated assemblages, differ from one carbonatite–phoscorite layer to another, suggesting a strong control of the mechanical sorting in the formation of Cu-sulfide textures within the Loolekop carbonatite. The alternation of carbonatite and phoscorite within the intrusion suggest that the Loolekop Pipe was emplaced through a series of successive magma pulses, which differentiated into carbonatite and phoscorite by melt immiscibility/progressive fractional crystallisation and pressure drop. Three-dimensional textural analysis represents an effective tool for the characterisation of magma flow and is useful for the understanding of magmatic processes controlling sulfide liquid-bearing phoscorite–carbonatite magmas.

The new mineral bianchiniite, Ba2(Ti4+V3+)(As2O5)2OF, has been discovered in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. It occurs as brown {001} tabular crystals, up to 1 mm across, with a vitreous lustre. It is brittle, with a perfect {001} cleavage. Streak is brownish. In reflected light, bianchiniite is grey, with orange–yellow internal reflections. It is weakly bireflectant, with a very weak anisotropy in shades of grey. Minimum and maximum reflectance data for COM wavelengths [Rmin/Rmax (%), (λ, nm)] are: 5.0/5.8 (470), 5.7/6.5 (546), 5.7/7.0 (589) and 5.2/6.3 (650). Electron microprobe analyses gave (wt.% – average of 10 spot analyses): TiO2 10.34, V2O3 3.77, Fe2O3 3.76, As2O3 44.36, Sb2O3 0.22, SrO 0.45, BaO 34.79, PbO 0.28, F 1.77, sum 99.74, –O = F –0.75, total 98.99. On the basis of 12 anions per formula unit, the empirical formula of bianchiniite is (Ba2.00Sr0.04Pb0.02)Σ2.06(Ti4+1.14V3+0.44Fe3+0.42)Σ2.00[(As3.96Sb0.02)Σ3.98O10](O1.18F0.82)Σ2.00. Bianchiniite is tetragonal, space group I4/mcm, with unit-cell parameters a = 8.7266(4), c = 15.6777(7) Å, V = 1193.91(12) Å3 and Z = 8. Its crystal structure was refined from single-crystal X-ray diffraction data to R1 = 0.0134 on the basis of 555 unique reflections with Fo > 4σ(Fo) and 34 refined parameters. The crystal structure shows columns of corner-sharing [Ti/(V,Fe)]-centred octahedra running along c, connected along a and b through (As2O5) dimers. A {001} layer of Ba-centred [10+2]-coordinated polyhedra is intercalated between (As2O5) dimers. Bianchiniite has structural relations with fresnoite- and melilite-group minerals. The name honours the two mineral collectors Andrea Bianchini (b. 1959) and Mario Bianchini (b. 1962) for their contribution to the knowledge of the mineralogy of pyrite ± baryte ± iron-oxide ore deposits from the Apuan Alps.

Scar Crags and Dale Head North in the English Lake District host mineralised veins enriched in ‘Energy Critical Elements’ (ECEs) specifically, bismuth, cobalt and copper. A limited number of studies in the 1970s investigated the mineralogy and inferred the genesis of these veins as being related to the intrusion of the Lake District batholith.

This study investigates the geology, mineralogy, composition and paragenesis of these two mineralised areas. The results highlight the ubiquitous presence of Co–Fe–Ni-sulfarsenides in both deposits and the presence of some mineral species, hitherto unreported. Scar Crags samples contained high concentrations of cobalt, commonly present within arsenopyrite, whereas cobalt is of minor importance at Dale Head North, where copper and arsenic are the primary metals. A sequence of events, with As–Co–Ni-bearing fluids infilling the veins after an initial stage of quartz and chlorite precipitation is the most striking resemblance between the two mineralised systems, potentially indicating a common process for Co-rich vein-type deposits in the area. If so, understanding such processes could prove vital in aiding exploration in other terranes.

Ontology deals with questions concerning what things exist, and how such things may be associated according to similarities and differences and related within a hierarchy. Ontology provides a rigorous way to develop a general definition of a mineral species. Properties may be divided into two principal groups: an intrinsic property is characteristic of the object and is independent of anything else; an extrinsic property depends on the relation between the object and other things. A universal is an entity that is common to all objects in a set. Here the objects are mineral samples, each entity is a specific property of these minerals, and the set of objects is all mineral samples of that mineral species. The key intrinsic properties of a mineral species are its name, its end-member formula and Z (the number of formula units in the unit cell), its space group and the bond topology of the end-member structure. These are also universals as they are common to all mineral samples belonging to that mineral species. An archetype is a pure form which embodies the fundamental characteristics of an object. Thus the archetype of a mineral species embodies the above set of universals. Real mineral samples of this mineral species are imperfect copies of that archetype, with a range of chemical composition defined by the boundaries between end-member formulae of this and other end members of the same bond topology. The result is a formal definition of a mineral species: A specific mineral species is the set of imperfect copies of the corresponding archetype and is defined by the following set of universals: name, end-member formula and Z, space group, and bond topology of the end-member structure, with the range of chemical composition limited by the compositional boundaries between end members with the same bond topology.