The Oligo–Miocene Ardestan quartz diorite to tonalite is part of widespread Cenozoic magmatism within the Urumieh–Dokhtar Magmatic Assemblage of Iran. The Ardestan pluton is composed mainly of varying proportions of plagioclase feldspar (normally zoned from bytownite to andesine), amphibole (magnesio-hornblende) and biotite. Biotite exhibits a range of Al values (~2–2.8 apfu) over very restricted Fe# ratios (0.42–0.56) which are characteristic of continental arc magmatic suites. High Ti2O contents of biotite (<6.1 wt.%) suggest a magmatic origin. Ti-in-biotite geothermometery gives a mean crystallisation temperature of 730 ± 56°C, slightly higher than calculated TZr.Ti°C (716 ± 50°C) and similar to the average TZr.sat°C (735 ± 26°C). These results are consistent with the low bulk-rock SiO2 contents, which provide minimum estimates of temperature and indicate zircon crystallised from a fractionated magma. Zircons from the Ardestan pluton have high (Sm/La)N (>10) ratios suggesting a magmatic origin. T–$f_{{\rm O}_{\rm 2}}$ calculations of oxygen fugacity between –13.6 to –16.9 indicate oxidising crystallisation conditions between the Ni–NiO (NNO) and Fe2O3–Fe3O4 (HM) buffers. Tight linear trends of log (XF/XOH), log (XCl/XOH) and log (XCl/XOH) vs. XMg represent a narrow range of $f_{{\rm H}_2O}$, fHF and fHCl, clearly indicating that physico-chemical conditions were essentially constant throughout the formation of magmatic biotite. The shape of crystal size distribution curves along with the medium Al and Mg contents in amphibole and biotite, respectively, are consistent with a history of magma mixing involving injections of basic magma into the evolving felsic chamber. Calculated residence time for Ardestan plagioclase crystals of ~630 years support field evidence that these plutons were emplaced at shallow depths.

The new mineral antofagastaite, ideally Na2Ca(SO4)2·1.5H2O, was found in the oxidation zone of sulfide–quartz veins at the abandoned Coronel Manuel Rodríguez mine, Mejillones, Antofagasta Province, Antofagasta Region, Chile. It is associated with sideronatrite, metasideronatrite, aubertite, gypsum, ferrinatrite, glauberite, amarillite and an unidentified Fe phosphate. Antofagastaite occurs as prismatic crystals up to 0.5 mm × 1 mm × 5 mm, elongated along [010], typically combined in open-work aggregates up to 1 cm across. Antofagastaite is transparent and colourless, with vitreous lustre. It is brittle; the Mohs’ hardness is ca 3. Cleavage is distinct on (001). Dmeas. is 2.42(1) and Dcalc. is 2.465 g cm−3. Antofagastaite is optically biaxial (–), α = 1.489(2), β = 1.508(2), γ = 1.510(2) and 2Vmeas. = 40(10)°. The IR spectrum is reported. Chemical composition (wt.%, electron microprobe, H2O determined by gas chromatography) is: Na2O 20.85, CaO 17.42, SO3 52.56, H2O 7.93, total 98.76. The empirical formula (based on 8 O atoms belonging to sulfate anions per formula unit with all H belonging to H2O molecules) is Na2.06Ca0.95S2.01O8·1.35H2O. Antofagastaite is monoclinic, P21/m, a = 6.4596(4), b = 6.8703(5), c = 9.4685(7) Å, β = 104.580(4)°, V = 406.67(5) Å3 and Z = 2. The strongest reflections of the powder XRD pattern [d, Å (I, %) (hkl)] are: 9.17 (100) (001), 5.501 (57) (011), 3.437 (59) (020), 3.058 (43) (003), 2.918 (50) (2¯11), 2.795 (35) (013) and 2.753 (50) (121, 201). The crystal structure was solved based on single-crystal X-ray diffraction data, R1 = 5.71%. The structure of antofagastaite consists of ordered and disordered blocks and is related to syngenite K2Ca(SO4)2·H2O. Incorporation of additional H2O molecules in the syngenite-type structure results in disorder of the one of the two tetrahedral sulfate groups occurring in antofagastaite. In addition to the above-reported type material, antofagastaite together with syngenite and blödite occurs in the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia.

The mineral ‘oboyerite’, first described in 1979 from the Grand Central mine, Tombstone, Cochise County, Arizona, USA, has been re-examined. The type specimen from the Natural History Museum, London and a specimen from the Natural History Museum of Los Angeles County (traceable to S. A Williams, who first described ‘oboyerite’) were analysed in this study. The discreditation of ‘oboyerite’ as a valid mineral species has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (Proposal 19-D). Single-crystal X-ray diffraction, powder X-ray diffraction, electron probe microanalysis and scanning electron microscopy were all employed to show that ‘oboyerite’ is formed of at least two distinct phases, including the lead–tellurium oxysalt minerals ottoite and plumbotellurite. During the course of the discreditation, plumbotellurite was confirmed to be identical to the synthetic compound α-Pb2+Te4+O3. Previously, in some mineralogical literature plumbotellurite was described as orthorhombic with no known crystal structure.

The new mineral lussierite (IMA2018-101), Na10[(UO2)(SO4)4](SO4)2(H2O)3, was found in the Blue Lizard mine, San Juan County, Utah, USA, where it occurs as pale green–yellow prisms or blades in a secondary assemblage with belakovskiite, ferrinatrite, halite, ivsite, metavoltine and thénardite. The streak is white and the fluorescence is bright cyan under 365 nm ultraviolet light. Crystals are transparent with vitreous lustre. The tenacity is brittle, the Mohs hardness is 2½, the fracture is irregular and no cleavage was observed. The mineral is easily soluble in H2O and has a measured density of 2.87(2) g cm–3. Lussierite is optically biaxial (+), with α = 1.493(1), β = 1.505(1) and γ = 1.518(1) (white light); 2Vmeas. = 88(1)°; dispersion is r > v, moderate; pleochroism: X = colourless, Y and Z = green yellow (X < Y ≈ Z); optical orientation: X = b, Z ∧ a = 44° in obtuse β. Electron microprobe analyses (wavelength-dispersive spectroscopy mode) provided Na10(U0.99O2)(S1.00O4)6·3H2O (+0.06 H for charge balance). The five strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 6.69(95)($\bar{1}$11,130), 4.814(100)(150,002,060), 3.461(83)(171,$\bar{2}$02), 2.955(81)(113,330) and 2.882(74)($\bar{1}$91,311,191,0·10·0). Lussierite is monoclinic, Cc, a = 9.3134(4), b = 28.7501(11), c = 9.6346(7) Å, β = 93.442(7)°, V = 2575.1(2) Å3 and Z = 4. The structure (R1 = 0.0298 for 5202 I > 2σI) contains a [(UO2)(SO4)4]6– uranyl sulfate cluster in which one SO4 tetrahedron shares an edge (bidentate linkage) with the UO7 pentagonal bipyramid. The uranyl sulfate clusters occur in layers and are linked through a complex network of bonds involving Na+ cations, isolated SO4 tetrahedra and isolated H2O groups.

The migration and accumulation of immiscible silicate liquids may play a significant role in the differentiation of crustal magma bodies and the formation of some economic mineral deposits. However, our understanding of the processes that control the segregation of these liquids is currently limited by the short timescales of petrological experiments. Detailed microstructural investigations of Palaeogene basaltic dykes from Northeast England, coupled with simple 1D thermal models, constrain the effects of cooling rate on the microstructure of unmixed immiscible silicate liquids under natural conditions. The size of unmixed Fe-rich droplets within a continuous silicic phase is related to the cooling rate by a power law, with droplet diameter increasing with decreasing cooling rate, accompanied by an increase in the number of droplets. Fe-rich droplet coarsening is a result of diffusion-controlled growth. The average apparent aspect ratio and grain size of matrix plagioclase crystals indicate that nucleation and growth of these grains probably occurred in a static (or only weakly convecting) fluid dynamical regime.

Bavsiite from the type locality Gun Claim, Yukon Territory, Canada, occurs as millimetre-sized sky-blue platy crystals in a barium-rich low-temperature skarn related to a porphyritic quartz monzonite stock. Associated minerals are alstonite, baryte, celsian, diopside, fresnoite, mica, suzukiite, walstromite, witherite and minerals of the cerchiaraite group. Bavsiite is optical uniaxial (+), with ω = 1.725(3) and ε = 1.750(3) (589 nm) and pleochroic. Electron microprobe analyses yielded the empirical formula Na0.02Ba1.98Ti0.16Fe2+0.03V4+1.80 Al0.05Si4.00O14 based on 14 oxygen atoms, the simplified chemical formula is Ba2V2Si4O14. Bavsiite is tetragonal, space group I4/m, a = 7.043(1), c = 11.444(2) Å and Z = 2 obtained from single crystal data at 100 K, which are in good agreement with cell parameters from powder diffraction data at 293 K: a = 7.051(1) Å and c = 11.470(1) Å. The eight strongest lines of the powder X-ray diffraction pattern are [d, Å (I,%)(hkl)]: 3.76(30)(112), 3.36(44)(013), 3.004(100)(022), 2.493(43)(220), 2.486(67)(114), 2.286(24)(222), 1.785(39)(116) and 1.763(25)(040). The crystal structure was refined to R = 0.0159 based upon 312 unique reflections with I > 2σ(I). The crystal structure of bavsiite comprises unbranched single [Si4O12]8– rings connected by [VO5]6– square pyramids and BaO12 polyhedra. It can also be considered as cage–like [Si4V2O18]12– clusters built by four SiO4 tetrahedra and two VO5 square pyramids. These clusters are cross–linked to form a pseudo-two-dimensional network (2D) parallel to (001) containing empty channels along the a axis and the 2D networks held together by Ba2+ ions located in channels parallel to the c axis. The structural formula is Ba2V2O2[Si4O12]. Bavsiite is polymorphic to suzukiite, BaVSi2O7, which is orthorhombic.

This paper presents the nomenclature of the rhodonite group accepted by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA). An overview of the previous studies of triclinic (space group P$\bar{1}$) pyroxenoids belonging to the rhodonite structure type, with a focus on their crystal chemistry, is given. These minerals have the general structural formula VIIM(5)VIM(1)VIM(2)VIM(3)VIM(4)[Si5O15]. The following dominant cations at the M sites are known at present: M(5) = Ca or Mn2+, M(1–3) = Mn2+; and M(4) = Mn2+ or Fe2+. In accordance with the nomenclature, the rhodonite group consists of three IMA-approved mineral species having the following the general chemical formulae: M(5)AM(1–3)B3M(4)C[Si5O15], where A = Ca or Mn2+; B = Mn2+; and C = Mn2+ or Fe2+. The end-member formulae of approved rhodonite-group minerals are as follows: rhodonite CaMn3Mn[Si5O15]; ferrorhodonite CaMn3Fe[Si5O15]; and vittinkiite MnMn3Mn[Si5O15].

Nipalarsite, Ni8Pd3As4, is a new platinum-group mineral discovered in the sulfide-bearing orthopyroxenite of the Monchetundra layered intrusion, Kola Peninsula, Russia (67°52′22″N, 32°47′60″E). Nipalarsite forms anhedral grains (5–80 µm in size) in intergrowths with sperrylite, kotulskite, hollingworthite, isomertieite, menshikovite, palarstanide, nielsenite and monchetundtraite enclosed in pentlandite, anthophyllite, actinolite and chlorite. Nipalarsite is brittle, has a metallic lustre and a grey streak. In plane-polarised light, nipalarsite is light grey with a blue tinge. Reflectance values in air (in %) are: 46.06 at 470 nm, 48.74 at 546 nm, 50.64 at 589 nm and 54.12 at 650 nm. Values of VHN20 fall between 400.5 and 449.2 kg.mm–2, with a mean value of 429.9 kg.mm–2, corresponding to a Mohs hardness of ~4. The average result of 27 electron microprobe wavelength dispersive spectroscopy analyses of nipalarsite is (wt.%): Ni 44.011, Pd 28.74, Fe0.32, Cu 0.85, Pt 0.01, Au 0.05, As 25.42, Sb 0.05, Te 0.39, total 99.85. The empirical formula (normalised to 15 atoms per formula unit) is: (Ni8.10Fe0.06)Σ8.16(Pd2.94Cu0.18)Σ3.12(As3.68Te0.03)Σ3.71 or, ideally, Ni8Pd3As4. Nipalarsite is cubic, space group Fm$\bar{3}$m, with a = 11.4428(9) Å, V = 1498.3(4) Å3 and Z = 8. The strongest lines in the powder X-ray diffraction pattern of synthetic Ni8Pd3As4 [d, Å (I) (hkl)] are: 2.859(10)(004), 2.623(6)(313), 2.557(6)(024), 2.334(11)(224), 2.201(35)(115,333), 2.021(100)(044), 1.906(8)(006,244) and 1.429(7)(008). The crystal structure was solved and refined from the single-crystal X-ray diffraction data of synthetic Ni8Pd3As4. The relation between natural and synthetic nipalarsite is illustrated by an electron back-scattered diffraction study of natural nipalarsite. The density calculated on the basis of the empirical formula of nipalarsite is 9.60 g.cm–3. The mineral name corresponds to the three main elements: Ni, Pd and As.

Aleutite, ideally [Cu5O2](AsO4)(VO4)·(Cu0.5□0.5)Cl, was found in the Yadovitaya fumarole of the Second scoria cone of the Great Fissure Tolbachik eruption, Kamchatka Peninsula, Russia. Aleutite occurs as individual crystals in the masses of polycrystalline anhydrite. Aleutite is monoclinic, C2/m, a = 18.090(2) Å, b = 6.2284(6) Å, c = 8.2465(9) Å, β = 90.597(2)°, V = 929.1(2) Å3 and Z = 4 (from single-crystal X-ray diffraction data). The empirical formula calculated on the basis of (As + V+Mo + Fe3+) = 2 atoms per formula unit is Сu5.40Zn0.05Ca0.01As1.09V0.84Mo0.04Fe0.03K0.05Pb0.02Rb0.01Cs0.01O9.97Cl1.07. The crystal structure was solved by direct methods and refined to an agreement index R1 = 0.066. Aleutite has a new structure type. Aleutite is unique amongst natural and synthetic copper vanadates and arsenates, as it has As5+ and V5+ cations ordered over two tetrahedral sites. The topology of ${}_\infty ^1 [{\rm Cu_5O_2}]^{6 +} $ oxocentred bands in aleutite is novel and has not been described before in minerals and synthetic materials. The structural architecture of the ${}_\infty ^1 [{\rm Cu_5O_2}]^{6 +} $ band in aleutite can be derived from a kagome network and represents a one-dimensional slice from it. In addition, aleutite is an interesting and complex example of a natural salt-inclusion phase.

The Weaklaw vent in SE Scotland (East Lothian coast), inferred to be Namurian, produced lava spatter and volcanic bombs. The latter commonly contained ultramafic xenoliths. All were metasomatised by carbonic fluids rich in incompatible elements. The lavas and xenoliths are inferred to have been basanites and lherzolites prior to metasomatism. The abundance and size of (carbonated) peridotite xenoliths at Weaklaw denotes unusual rapidity of magma ascent and high-energy eruption making Weaklaw exceptional in the British Isles. The lavas and xenoliths were altered subsequently by low-temperature (<200°C) carbo-hydrous fluids to carbonate, clay and quartz assemblages. A small irregular tuffisite ‘dyke’ that transects the ejecta is also composed dominantly of carbonates and clays. The peridotitic xenoliths are typically foliated, interpreted as originating as pre-entrainment mantle shear-planes.

Analyses of the relic spinels shows them to be compositionally similar to spinels in local unaltered lherzolites from near-by basanitic occurrences. Chromium showed neither significant loss nor gain but was concentrated in a di-octahedral smectite allied to volkonskoite. It is in the complex association of smectite with other clays, chlorite and possibly fuchsite that the diverse incompatible elements are concentrated.

We conclude that late Palaeozoic trans-tensional fault movement caused mantle shearing. Rapid ascent of basanite magma entrained large quantities of sheared lithospheric mantle. This was followed by ascent of an aggressive carbonate-/ hydroxyl-rich fluid causing pervasive metasomatism. The vent is unique in several ways: in its remarkable clay mineralogy and in displaying such high Cr-clays in a continental intra-plate setting; in being more productive in terms of its ‘cargo’ of peridotite xenoliths; in presenting an essentially un-eroded sequence of Namurian extrusives; and, not least, for giving evidence for post-eruptive, surface release of small-melt, deep-source fluids.

Davidbrownite-(NH4), (NH4,K)5(V4+O)2(C2O4)[PO2.75(OH)1.25]4·3H2O, is a new mineral species from the Rowley mine, Maricopa County, Arizona, USA. It occurs in an unusual bat-guano-related, post-mining assemblage of phases that include a variety of vanadates, phosphates, oxalates and chlorides, some containing NH4+. Other secondary minerals found in association with davidbrownite-(NH4) are antipinite, fluorite, mimetite, mottramite, quartz, rowleyite, salammoniac, struvite, vanadinite, willemite and wulfenite. Crystals of davidbrownite-(NH4) are light green–blue needles or narrow blades up to ~0.2 mm long. The streak is white, the lustre is vitreous, Mohs hardness is ca. 2, tenacity is brittle and fracture is splintery. There are two good cleavages in the [010] zone, probably {100} and {001}. The measured density is 2.12(2) g cm–3. Davidbrownite-(NH4) is optically biaxial (+) with α = 1.540(2), β = 1.550(5) and γ = 1.582(2) (white light); 2V = 58.5(5)°; moderate r > v dispersion; and orientation Z = b and Y ≈ a. Pleochroism: X = pale blue, Y = nearly colourless, Z = light blue; and Y < X < Z. Electron microprobe analysis gave the empirical formula [(NH4)3.11K1.73Na0.09]Σ4.93[(V4+1.92Mg0.01Al0.02)Σ1.95O2](C2O4) [(P3.94As0.12)Σ4.06O10.94(OH)5.06]·3H2O, with the C and H content provided by the crystal structure. Raman and infrared spectroscopy confirmed the presence of NH4 and C2O4. Davidbrownite-(NH4) is monoclinic, P21/c, with a = 10.356(6), b = 8.923(5), c = 13.486(7) Å, β = 92.618(9)°, V = 1244.9(12) Å3 and Z = 2. The crystal structure of davidbrownite-(NH4) (R1 = 0.0524 for 2062 Io > 2σI reflections) consists of a chain structural unit with the formula {(V4+O)2(C2O4)[PO2.75(OH)1.25]4}5–, and a disordered interstitial complex containing five large monovalent cations (NH4+ and K+) and three H2O groups pfu. Strong hydrogen bonds form links within and between the chains.

The new mineral zubkovaite, Ca3Cu3(AsO4)4, was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. It is associated with anhydrite, svabite, hematite, johillerite, tilasite, fluorophlogopite, sanidine and aphthitalite. Zubkovaite occurs as coarse prismatic crystals up to 0.01 mm × 0.01 mm × 0.2 mm combined in radiating aggregates or crusts. The mineral is transparent, bright sky-blue, turquoise-coloured or light bluish-green, with vitreous lustre. It is brittle, with imperfect cleavage. The Mohs’ hardness is ca 3. Dcalc is 4.161 g cm–3. Zubkovaite is optically biaxial (–), α = 1.747(5), β = 1.774(5), γ = 1.792(5) and 2Vmeas = 75(10)°. Chemical composition (wt.%, electron microprobe) is: CaO 19.22, CuO 27.37, As2O5 52.54, SO3 0.67, total 99.80. The empirical formula based on 16 O apfu is Ca2.96Cu2.97(As3.945S0.07)Σ4.015O16. Zubkovaite is monoclinic, C2, a = 16.836(3), b = 5.0405(8), c = 9.1173(17) Å, β = 117.388(13)°, V = 687.0(2) Å3 and Z = 2. The strongest reflections of the powder XRD pattern [d,Å (I) (hkl)] are: 7.44 (100) ($\bar 2$01), 3.727 (79) (400, $\bar 2$02, $\bar 3$11), 3.334 (92) ($\bar 1$12), 2.914 (73) (311), 2.765 (50) ($\bar 6$01, $\bar 6$02), 2.591 (96) ($\bar 3$13) and 2.521 (53) (020). The crystal structure is unique for minerals. It was solved from single-crystal X-ray diffraction data to R = 7.19%. The structure contains trimers of Cu2+-centred polyhedra (consisting of one distorted square CuO4 in the core and two distorted square pyramids CuO5) and two crystallographically independent As5+O4 tetrahedra playing different roles: As(2)O4 tetrahedra link neighbouring trimers into ribbons whereas As(1)O4 tetrahedra link adjacent ribbons into heteropolyhedral layers; Ca cations are located in the interlayer space. The mineral is named in honour of the Russian crystallographer and crystal chemist Natalia Vital'evna Zubkova (born 1976).