A reinvestigation of the type specimen of wadalite, ideally Ca12Al10Si4O32Cl6, from Tadano, Fukushima Prefecture, Japan, reveals that it has well-defined chemical sector zoning. The mineral occurs in skarn xenoliths in two-pyroxene andesite and forms tris-tetrahedral crystals up to 1 mm in size. The mineral is cubic, I¯43d, with a = 12.009(2) Å, V = 1731.8(8) Å3 and Z = 2. The zoning is divided into two sectors, {21¯1} and {211}, on the basis of back-scattered-electron images. The {21¯1} sector is more enriched in Fe3+, Si, Mg and Cl, and depleted in Al than the {211} sector. The empirical formulae yielded by the averaged compositions for the {21¯1} and {211} sectors are: Ca12.01(Al7.88$\hbox{Fe}_{{\rm 0}{\rm. 99}}^{{\rm 3 +}} $Si4.51Mg0.56Ti0.05)Σ13.99O32.22Cl5.55 and Ca12.05(Al8.42$\hbox{Fe}_{{\rm 0}{\rm. 85}}^{{\rm 3 +}} $Si4.20Mg0.44Ti0.04)Σ13.95O32.19Cl5.38, respectively. Compositional variations in the wadalite grains suggest that the Si contents are controlled mainly by the substitution T(Al,Fe3+) + W□ ↔ TSi + W(Cl,F). The presence of sector zoning suggests that the wadalite grew during rapid non-equilibrium crystallization.

The borate mineral satimolite, which was first described in 1969 and remained poorly-studied until now, has been re-investigated (electron microprobe analysis, single-crystal and powder X-ray diffraction studies, crystal-structure determination, infrared spectroscopy) and redefined based on the novel data obtained for the holotype material from the Satimola salt dome and a recently found sample from the Chelkar salt dome, both in North Caspian Region, Western Kazakhstan. The revised idealized formula of satimolite is KNa2(Al5Mg2)[B12O18(OH)12](OH)6Cl4·4H2O (Z = 3). The mineral is trigonal, space group R$\bar{3}$m, unit-cell parameters are: a = 15.1431(8), c = 14.4558(14) Å and V = 2870.8(4) Å3 (Satimola) and a = 15.1406(4), c = 14.3794(9) Å and V = 2854.7(2) Å3 (Chelkar). The crystal system and unit-cell parameters are quite different from those reported previously. The crystal structure of the sample from Chelkar was solved based on single-crystal data (direct methods, R = 0.0814) and the structure of the holotype from Satimola was refined on a powder sample by the Rietveld method (Rp = 0.0563, Rwp = 0.0761 and Rall = 0.0667). The structure of satimolite is unique for minerals. It contains 12-membered borate rings [B12O18(OH)12] in which BO3 triangles alternate with BO2(OH)2 tetrahedra sharing common vertices, and octahedral clusters [M7O6(OH)18] with M = Al5Mg2 in the ideal case, with sharing of corners between rings and clusters to form a three-dimensional heteropolyhedral framework. Each borate ring is connected with six octahedral clusters: three under the ring and three over the ring. Large ellipsoidal cages in the framework host Na and K cations, Cl anions and H2O molecules.

This study presents a complete characterization of kenoplumbomicrolite, (Pb,□)2Ta2O6[□,(OH),O], occurring in an amazonite pegmatite from Ploskaya Mountain, Western Keivy Massif, Kola Peninsula, Murmanskaja Oblast, Northern Region, Russia.

Kenoplumbomicrolite occurs in yellowish brown octahedral, cuboctahedral and massive crystals, up to 20 cm, has a white streak, a greasy lustre and is translucent. The Mohs hardness is ~6. Attempts to measure density (7.310–7.832 g/cm3) were affected by the ubiquitous presence of uraninite inclusions. Reflectance values were measured in air and immersed in oil. Kenoplumbocrolite is optically isotropic. The empirical formula is (Pb1.30□0.30Ca0.29Na0.08U0.03)Σ2.00(Ta0.82Nb0.62Si0.23Sn4+0.15Ti0.07Fe3+0.10Al0.01)Σ2.00O6[□0.52(OH)0.25O0.23]Σ1.00 (from the crystal used for the structural study) and (Pb1.33□0.66Mn0.01)Σ2.00(Ta0.87Nb0.72Sn4+0.18Fe3+0.11W0.08Ti0.04)Σ2.00O6[□0.80(OH)0.10O0.10]Σ1.00 (average including additional fragments). The mineral is cubic, space group Fd$\overline 3 $m. The unit-cell parameters refined from powder X-ray diffraction data are a = 10.575(2) Å and V = 1182.6(8) Å3, which are in accord with those obtained previously from a single crystal of a = 10.571(1) Å, V = 1181.3(2) Å3 and Z = 8. The mineral description and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2015-007a).

Ammoniovoltaite, (NH4)2Fe2+5Fe3+3Al(SO4)12(H2O)18, is a new voltaite-group mineral. The mineral was discovered at the Severo-Kambalny (North-Kambalny) geothermal field, Kambalny volcanic ridge, Southern Kamchatka, Russia. Ammoniovoltaite forms at ~100°C around geothermal gas/steam vents in association with alunogen, tschermigite and pyrite. Crystals of ammoniovoltaite have euhedral habit, are up to 50 µm in size and grow on alunogen plates. Ammoniovoltaite is black with vitreous lustre, opaque, brittle and water-soluble. Neither cleavage nor parting is found, the fracture is conchoidal. The mineral is isotropic, with the refractive index n = 1.602(2) (589 nm). Infrared spectra contain an absorption band at 1433 cm–1 distinctive for the ammonium ion. The chemical composition is (iron content is given in accordance with Mössbauer data, H2O calculated from a crystal-structure refinement, wt.%): FeO 13.26, Fe2O3 11.58, MgO 2.33, ZnO 0.04, Al2O3 2.74, SO3 47.46, K2O 0.19, CaO 0.11, (NH4)2O 2.96, H2O 16.03, total 96.70. The empirical formula based on S = 12 atoms per formula unit is [(NH4)1.88K0.08Ca0.04]Σ2.00(Fe2+3.74Mg1.17Fe3+0.05Zn0.01)Σ4.97(Fe3+2.89Al0.09)Σ2.98Al1.00(SO4)12.00(H2O)18.00. The crystal structure has been refined to R1 = 0.031 and 0.030 on the basis of 1217 and 1462 unique reflections with I >2σ(I) collected at 100 K and room temperature, respectively. Ammoniovoltaite is the ammonium analogue of voltaite. The mineral is cubic, Fd$\bar{3}$c, a = 27.250(1) Å and V = 20234(3) Å3 (at 100 K); and a = 27.322(1) Å and V = 20396(3) Å3 (at RT), with Z = 16. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 9.67 (74) (022), 7.90 (56) (222), 5.58 (84) (422), 3.560 (100) (731), 3.418 (100) (008) and 2.8660 (37) (931). A brief review of ammonium minerals from various volcanically active geological environments is given.

Belousovite, ideally KZn(SO4)Cl, was found in a Yadovitaya fumarole of the Second scoria cone of the North Breach of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Belousovite occurs as irregularly-shaped grains and in the form of microcrystalline masses associated with kamchatkite, langbeinite, euchlorine, anglesite and zincite. Belousovite is monoclinic, P21/c, a = 6.8904(5), b = 9.6115(7), c = 8.2144(6) Å, β = 96.582(2), V = 540.43(7) Å3 and Z = 4 (from single-crystal diffraction data). The eight strongest lines of the powder X-ray diffraction pattern are [dmeas Å(I)(hkl)]: 6.8451(100)(100), (3.6401)(71)($\bar{1}$21), (3.1592)(84)(1$\bar{1}$2), (3.1218)(41)($\bar{2}$11), (3.1140)(52)(022), (2.9812)(41)(031), (2.9121)(44)(130) and (2.0483)(19)($\bar{3}$12). The chemical composition determined by the electron-microprobe analysis is (wt.%): K2O 19.55, Rb2O 0.58, ZnO 34.85, SO3 34.65, Cl 14.77, –O = Cl2 3.34, total 101.06. The empirical formula based on O + Cl = 5 apfu is K0.97Rb0.01Zn1.00S1.01O4.03Cl0.97. The simplified formula is KZn(SO4)Cl. The crystal structure was solved by direct methods and refined to R1 = 0.029 on the basis of 1965 independent observed reflections. The structure of belousovite consists of infinite [ZnSO4Cl]– layers and K+ ions. [ZnSO4Cl]– layers are formed by corner sharing mixed-ligand ZnO3Cl tetrahedra and SO4 tetrahedra. The topology of [ZnSO4Cl]– layers in belousovite is identical to [Si4O10]4– layers in the minerals of the apophyllite group. A review of mixed-ligand ZnOmCln coordination polyhedra in minerals and inorganic compounds is given.

The new mineral markeyite (IMA2016-090), Ca9(UO2)4(CO3)13·28H2O, was found in the Markey mine, San Juan County, Utah, USA, where it occurs as a secondary phase on asphaltum in association with calcite, gypsum and natrozippeite. The mineral is pale yellowish-green with white streak and fluoresces bright bluish white under a 405 nm laser. Crystals are transparent and have vitreous to pearly lustre. It is brittle, with Mohs hardness 1½ to 2, irregular fracture and three cleavages: perfect on {001}; good on {100} and {010}. The measured density is 2.68 g cm–3. Crystals are blades, flattened on {001} and elongate on [010], exhibiting the forms {100}, {010}, {001}, {110}, {101}, {011} and {111}. Markeyite is optically biaxial (–) with α = 1.538(2), β = 1.542(2) and γ = 1.545(2) (white light); the measured 2V is 81(2)°; the dispersion is r < v (weak); the optical orientation is X = c, Y = b, Z = a; and pleochroism is X = light greenish yellow, Y and Z = light yellow (X > Y ≈ Z). Electron microprobe analyses (energy-dispersive spectroscopy mode) yielded CaO 18.60, UO3 42.90, CO2 21.30 (calc.) and H2O 18.78 (calc.), total 101.58 wt.% and the empirical formula Ca8.91(U1.01O2)4(CO3)13·28H2O. The six strongest powder X-ray diffraction lines are [dobs Å(I)(hkl)]: 10.12(69)(001), 6.41(91)(220,121), 5.43(100)(221), 5.07(33)(301,002,131), 4.104(37)(401,141) and 3.984(34)(222). Markeyite is orthorhombic, Pmmn, a = 17.9688(13), b = 18.4705(6), c = 10.1136(4) Å, V = 3356.6(3) Å3 and Z = 2. The structure of markeyite (R1 = 0.0435 for 3427 Fo > 4σF) contains uranyl tricarbonate clusters (UTC) that are linked by Ca–O polyhedra forming thick corrugated heteropolyhedral layers. Included within the layers is an additional disordered CO3 group linking the Ca–O polyhedra. The layers are linked to one another and to interlayer H2O groups only via hydrogen bonds. The structure bears some similarities to that of liebigite.

The crystal structures of carlfrancisite, ideally Mn32+(Mn2+,Mg,Fe3+,Al)42(As3+O3)2(As5+O4)4[(Si,As5+)O4]8(OH)42, hexagonal (rhombohedral), R3̄m with Z = 6, and unit-cell parameters: a = 8.2238(2), c = 205.113(6) Å and V = 12013.5(4) Å3, from the Kombat mine, Otavi Valley, Namibia, and mcgovernite, ideally Zn3(Mn2+,Mg,Fe3+,Al)42(As3+O3)2(As5+O4)4[(Si,As5+)O4]8(OH)42, hexagonal (rhombohedral), R3̄m with Z = 6, and unit-cell parameters: a = 8.2061(3), c = 204.118(8) Å and V = 11903.8(6) Å3, from Sterling Hill, New Jersey, have been solved by direct methods and refined to R1 values of 3.37 and 5.02% for 3837 and 3772 unique observed reflections, respectively; they are isostructural. Chemical analysis by electron microprobe and crystal-structure refinement gave the following compositions: carlfrancisite: As2O5 12.89, As2O3 3.33, P2O5 0.50, V2O5 0.74, SiO2 8.96, Al2O3 0.78, FeO 0.22, MnO 53.25, MgO 9.37, H2O(calc) 8.42, sum 98.50 wt.%; mcgovernite: As2O5 13.06, As2O3 3.71, SiO2 9.34, Al2O3 0.20, FeO 1.38, MnO 44.58, ZnO 8.81, MgO 8.89, H2O(calc) 8.24, sum 98.21 wt.%. The H2O contents and the valence states of As were determined by crystal-structure analysis.

There are 18 crystallographically distinct cation sites in both carlfrancisite and mcgovernite. There are two [4]-coordinated As sites fully occupied by As5+, and four T sites occupied by Si and As5+ in solid solution. The As(3) site has triangular pyramidal coordination with <As(3)–O> distances of 1.808 and 1.817 Å, typical of As3+. The Z(1) site, occupied by Mn2+ in carlfrancisite and Zn in mcgovernite, has tetrahedral coordination, and the Z(2) site is only partly occupied by Mg and Mn2+ in both structures. There are nine M sites, all of which are octahedrally coordinated and contain dominantly Mn2+ and Mg, with minor Al and Fe. There are three cation sites with significant vacancies: As(3), Z(2), M(3), and there are complicated patterns of short-range order involving the cations and vacancies at these sites.

The carlfrancisite–mcgovernite structure contains 84 layers of approximately close-packed polyhedra along one translation on c. The anions in the structure are arranged in approximately close-packed layers orthogonal to the c axis. Fourteen layers stack along the c axis in the sequence |**hhchch•hchchh| (* denotes a layer of anions displaced from close packed). There are eight distinct layers of cation-centred polyhedra that repeat via a centre of symmetry at the origin, and via the R-centering to give 84 layers per unit-cell.

The hydrated carbonate mineral ikaite (CaCO3·6H2O) is thermodynamically unstable at all known conditions on Earth. Regardless, ikaite has been found in marine sediments, as tufa columns and in sea ice. The reason for these occurrences remains unknown. However, cold temperatures (<6°C), high pH and the presence of Mg2+ and SO42– in these settings have been suggested as factors that promote ikaite formation. Here we show that Mg concentration and pH are primary controls of ikaite precipitation at 5°C. In our experiments a sodium carbonate solution was mixed with seawater at a temperature of 5°C and at a constant rate. To test the effect of Mg2+ and SO42– we used synthetic seawater which allowed us to remove these elements from the seawater. The pH was controlled by different ratios of Na2CO3 and NaHCO3 in the carbonate solution. We found that ikaite precipitated when both seawater and synthetic seawater from which SO4 had been removed were used in the experiments. However, ikaite did not precipitate in experiments conducted with synthetic seawater from which Mg had been removed. In these experiments, calcite precipitated instead of ikaite. By varying the Mg concentration of the synthetic seawater and the pH of the sodium carbonate solution, we constructed a kinetic stability diagram for ikaite and calcite as a function of Mg concentration and pH. One possible explanation of our finding is that Mg2+ inhibits calcite nucleation and thereby allows metastable ikaite to form instead.

Tombarthite-(Y) is discredited as a mineral species. No type material was available, but material used for the original description has been located and neotype material defined. The main reason for the erroneous description of tombarthite-(Y) is the result of chemical analyses being carried out on heated material, which removed elements such as C and F. New semi-quantitative chemical analyses show that at least F is present in the fresh material, but absent after a heating scheme identical to that of the original description. Modern powder X-ray diffraction methods (XRD) confirm that the material identified as tombarthite-(Y) is a mixture of metamict and crystalline phases. Consequently, what was known as tombarthite-(Y) is not a mixture of the same minerals in equal amounts in different samples, but mixtures of various minerals depending on the sample. The main minerals identified are thalénite-(Y), xenotime-(Y) and kainosite-(Y). The discreditation of tombarthite-(Y) relies on new analyses of a large number of samples from the collection of the Natural History Museum (NHM) in Oslo and has been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (proposal 16-K).

Structural data for weishanite, an alloy of Au, Ag and Hg, were collected for the first time from a crystal from the Keystone Mine, Colorado, USA. The structure was solved in the space group P63/mmc with the unit cell a = 2.9348(8) and c = 4.8215(18) Å] and refined to R = 0.0299 for 40 observed reflections [4σ(F) level] and four parameters and to R = 0.0356 for all 47 independent reflections. The weishanite structure can be considered a derivative of the zinc structure, with Au, Ag and Hg disordered in the same structural position. On this basis, we suggest that the formula is normalized to 1 atom with Z = 2, leading, for the sample investigated, to Au0.41Ag0.31Hg0.28 (electron microprobe data). Accordingly, weishanite can be considered the Au-rich isotype of schachnerite. A comparison with other Au/Ag-Hg alloys is presented together with a critical discussion about the nomenclature rules to be applied to alloys and simple metals.

The Icelandic crust is characterized by low δ18O values that originate from pervasive high-temperature hydrothermal alteration by 18O-depleted meteoric waters. Igneous rocks in Iceland with δ18O values significantly higher than unaltered oceanic crust (~5.7‰) are therefore rare. Here we report on rhyolitic intra-caldera samples from a cluster of Neogene central volcanoes in Borgarfjörður Eystri, Northeast Iceland, that show whole-rock δ18O values between +2.9 and +17.6‰ (n = 6), placing them among the highest δ18O values thus far recorded for Iceland. Extra-caldera rhyolite samples from the region, in turn, show δ18O whole-rock values between +3.7 and +7.8‰ (n = 6), consistent with the range of previously reported Icelandic rhyolites. Feldspar in the intra-caldera samples (n = 4) show δ18O values between +4.9 and +18.7‰, whereas pyroxene (n = 4) shows overall low δ18O values of +4.0 to +4.2‰, consistent with regional rhyolite values. In combination with the evidence from mineralogy and rock H2O contents, the high whole-rock δ18O values of the intra-caldera rhyolites appear to be the result of pervasive isotopic exchange during subsolidus hydrothermal alteration with 18O-enriched water. This alteration conceivably occurred in a near-surface hot spring environment at the distal end of an intra-caldera hydrothermal system, and was probably fed by waters that had already undergone significant isotope exchange with the country rock. Alternatively, 18O-enriched alteration fluids may have been produced during evaporation and boiling of standing water in former caldera lakes, which then interacted with the intra-caldera rock suites. Irrespective of the exact exchange processes involved, a previously unrecognized and highly localized δ18O-enriched rock composition exists on Iceland and thus probably within the Icelandic crust too.

The quartz-monzonitic intrusion of ‘Botro ai Marmi’ in Tuscany, Italy, can be considered to be a typical example of an intrusion-centred magmatic hydrothermal system. The evolution of hydrothermal fluids in the ‘Botro ai Marmi’ intrusion was investigated using fluid-inclusion analyses to provide suitable physico-chemical constraints on the fluids involved in the late- to post-magmatic hydrothermal activity that affected the intrusion, providing inferences on their origin and variations of temperature and pressure with time.

This work demonstrates that the earliest fluids circulating in the ‘Botro ai Marmi’ intrusion were high-temperature brines exsolved directly from the crystallizing magma. This fluid circulated in the intrusion under lithostatic conditions (P > 90 MPa, T > 540°C). A second evolutionary stage of the magmatic hydrothermal system is marked by the transition from lithostatic (>90 MPa) to hydrostatic dominated conditions (50 to 10 MPa). In this stage the fluids are also interpreted to be mainly orthomagmatic in origin but unmixed in a high-salinity brine and in a low-salinity vapour aqueous phase, at a temperature ranging from ~500 to 300°C. These fluids were responsible for the potassic alteration facies. At a later stage of hydrothermal evolution, abundant meteoric dominated fluids entered the system and are associated with propylitic alteration. This event marks the transition from a magmatic-hydrothermal system to a typical hydrothermal (‘geothermal’) system, which can be assumed to be similar to some extent to the nearby active high-enthalpy geothermal system of Larderello. Low-temperature and low-salinity meteoric water-dominated fluids characterize the latest stage of the ‘Botro ai Marmi’ hydrothermal system.

Ba-rich and Si-rich phlogopites occur in the talc-bearing rocks of the La Creuse sulfide ore deposit in Beaujolais, France. They form a group of compositions completely separated from the common Al-rich phlogopites that occur in the surrounding talc-free metasiltites and metarhyolites, with higher Ba and Mg and lower Al contents. The Ba-rich phlogopites have a relatively narrow compositional range (0.24 to 0.80 Ba per formula unit, for 44 valencies) with high and constant Si (5.8 atoms per formula unit, apfu) and Mg + Fe (5.6 apfu), probably buffered by the presence of talc. Compared to low-Al phlogopites from talc-free rocks, the excess charge introduced by the BaK–1 substitution is compensated by interlayer vacancies. Such a high level of interlayer vacancy (0.56 pfu), related to the talc-producing metasomatic conditions, is essential for the stability of this special group of Ba-rich and Si-rich phlogopites.

Single crystal X-ray diffraction analyses were performed. Ba-rich and Si-rich phlogopite is monoclinic, space group C2/m, (R = 5.31%) with a = 5.3185(5), b = 9.2136(9), c = 10.1349(11) Å and β = 100.131(11)°. The occupancies of Mg/Fe and K/Ba were refined exploring different vacancies. The solutions giving the best R factor (4.77%) and goodness-of-fit (1.06) are obtained with 15% < vacancy < 40% at the interlayer site.

The new mineral somersetite, has been found at Torr Works (‘Merehead quarry’) in Somerset, England, United Kingdom. Somersetite is green or white (typically it is similar visually to hydrocerussite-like minerals but with a mint-green tint), forms plates and subhedral grains up to 5 mm across and up to 2 mm thick. In bi-coloured crystals it forms very thin intergrowths with plumbonacrite. The empirical formula of somersetite is Pb8.00C5.00H4.00O20. The simplified formula is Pb8O(OH)4(CO3)5, which requires: PbO = 87.46, CO2 = 10.78, H2O = 1.76, total 100.00 wt.%.

The infrared spectrum of somersetite is similar to that of plumbonacrite and, to a lesser degree, hydrocerussite. Somersetite is hexagonal, P63/mmc, a = 5.2427(7), c = 40.624(6) Å, V = 967.0(3) Å3 and Z = 2. The eight strongest reflections of the powder X-ray diffraction (XRD) pattern [d,Å(I)(hkl)] are: 4.308(33)(103), 4.148(25)(104), 3.581(40)(107), 3.390(100)(108), 3.206(55)(109), 2.625(78)(110), 2.544(98)(0.0.16) and 2.119(27)(1.0.17). The crystal structure was solved from single-crystal XRD data giving R1 = 0.031. The structure of somersetite is unique and consists of the alternation of the electroneutral plumbonacrite-type [Pb5O(OH)2(CO3)3]0 and hydrocerussite-type [Pb3(OH)2(CO3)2]0 blocks separated by stereochemically active lone electron pairs on Pb2+. There are two blocks of each type per unit cell in the structure, which corresponds to the formula [Pb5O(OH)2(CO3)3][Pb3(OH)2(CO3)2] or Pb8O(OH)4(CO3)5 in a simplified representation. The 2D blocks are held together by weak Pb–O bonds and weak interactions between lone pairs.