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.

Potassic-jeanlouisite, ideally K(NaCa)(Mg4Ti)Si8O22O2, is the first characterised species of oxo amphibole related to the sodium–calcium group, and derives from potassic richterite via the coupled exchange CMg–1W${\rm OH}_{{\rm \ndash 2}}^{\ndash}{} ^{\rm C}{\rm Ti}_1^{{\rm 4 +}} {} ^{\rm W}\!{\rm O}_2^{2\ndash} $. The mineral and the mineral name were approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification, IMA2018-050. Potassic-jeanlouisite was found in a specimen of leucite which is found in the lava layers, collected in the active gravel quarry on Zirkle Mesa, Leucite Hills, Wyoming, USA. It occurs as pale yellow to colourless acicular crystals in small vugs. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: A(K0.84Na0.16)Σ1.00B(Ca0.93Na1.02Mg0.04${\rm Mn}_{{\rm 0}{\rm. 01}}^{2 +} $)Σ2.00C(Mg3.85${\rm Fe}_{{\rm 0}{\rm. 16}}^{2 +} $Ni0.01${\rm Fe}_{{\rm 0}{\rm. 33}}^{3 +} {\rm V}_{{\rm 0}{\rm. 01}}^{3 +} $Ti0.65)Σ5.01T(Si7.76Al0.09Ti0.15)Σ8.00O22W[O1.53F0.47]Σ2.00. The holotype crystal is biaxial (–), with α = 1.674(2), β = 1.688(2), γ = 1.698(2), 2Vmeas. = 79(1)° and 2Vcalc. = 79.8°. The unit-cell parameters are a = 9.9372(10), b = 18.010(2), c = 5.2808(5) Å, β = 104.955(2)°, V = 913.1(2) Å3, Z = 2 and space group C2/m. The strongest eight reflections in the powder X-ray pattern [d values (in Å) (I) (hkl)] are: 2.703 (100) (151); 3.380 (87) (131); 2.541 (80) ($\bar 2$02); 3.151 (70) (310); 3.284 (68) (240); 8.472 (59) (110); 2.587 (52) (061); 2.945 (50) (221,$\bar 1$51).

Fluorapatite with monazite-(Ce) and xenotime-(Y) microinclusions occurs in the lithium–caesium–tantalum pegmatite body A of the Volta Grande mine, Minas Gerais state, Southeast Brazil. The fluorapatite displays faint zoning, detected mainly by cathodoluminescence. Electron probe and laser ablation analyses indicate that zoning in the fluorapatite corresponds to variation in Mn and rare-earth element (REE) content. Such compositional variation is attributed to partial removal of the REE from the fluorapatite structure during a dissolution–reprecipitation process, forming monazite-(Ce) and xenotime-(Y) microinclusions in the REE-depleted zones of the fluorapatite. These inclusions exhibit an inherited geochemical signature, manifested by low Th and U concentrations when compared to monazite and xenotime crystallised from melts. Rhodochrosite and calcite inclusions are also associated with monazite-(Ce) and xenotime-(Y) and are probably products of the same process, recycling Ca, Mn, and CO32− from the fluorapatite through the following reaction: [Ca(5–2a–b–½x),Naa,(Y + REE)a,Mnb][(PO4)3–x(CO3)x(F)] + Fluid[a(2Ca2+ + P5+) + (x–b)(Ca2+) + H2O)] → [Ca5(PO4)3(F,OH)] + a[(Y + REE)PO4] + b[Mn(CO3)] + (x–b)[Ca(CO3)] + Fluid a[Na+].

On the basis of new fluid-inclusion analyses, we propose that a hot (T > 204.5°C), salty (16 wt.% eq. NaCl, attributed to LiCl), hydrous fluid mediated the dissolution–reprecipitation of the fluorapatite. This fluid corresponds to similarly described Li-rich fluids which were suggested to have re-equilibrated the mineralogical assemblage at the Volta Grande mine.

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.

Dokuchaevite, ideally Cu8O2(VO4)3Cl3, was found in the Yadovitaya fumarole of the Second scoria cone of the North Breach of the Great Tolbachik Fissure Eruption (1975–1976), Tolbachik volcano, Kamchatka Peninsula, Russia. Dokuchaevite occurs on the crusts of various copper sulfate exhalative minerals (such as kamchatkite and euchlorine) as individual prismatic crystals. Dokuchaevite is triclinic, P$\bar{1}$, a = 6.332(3), b = 8.204(4), c = 15.562(8) Å, α = 90.498(8), β = 97.173(7), γ = 90.896(13)°, V = 801.9(7) Å3 and R1 = 0.057. The eight strongest lines of the X-ray powder diffraction pattern are (d, Å (I)(hkl): (15.4396)(18)(00$\bar{1}$), (7.2762)(27)(0$\bar{1}$1), (5.5957)(43)(012), (4.8571)(33)($\bar{1}\bar{1}$1), (3.1929) (29)(023), (2.7915)(30)(202), (2.5645)(21)(032), (2.5220)(100)(1$\bar{3}$0), (2.4906)(18)(130) and (2.3267)(71)(2$\bar{2}$2). The chemical composition determined by electron-microprobe analysis is (wt.%): CuO 60.87, ZnO 0.50, FeO 0.36, V2O5 19.85, As2O5 6.96, SO3 0.44, MoO3 1.41, SiO2 0.20, P2O5 0.22, Cl 10.66, –O = Cl2 2.41, total 99.06. The empirical formula calculated on the basis of 17 anions per formula unit is (Cu7.72Zn0.06Fe0.05)Σ7.83(V2.20As0.61Mo0.10S0.06P0.03Si0.03)Σ3.03O13.96Cl3.04.

The crystal structure of dokuchaevite represents a new structure type with eight Cu sites, which demonstrate the remarkable diversity of Cu2+ mixed-ligand coordination environments. The crystal structure of dokuchaevite is based on OCu4 tetrahedra that share common corners thus forming [O2Cu6]8+ single chains. Two of the eight symmetrically independent copper atoms do not form Cu–O bonds with additional oxygen atoms, and thus are not part of the OCu4 tetrahedra, but provide the three-dimensional integrity of the [O2Cu6]8+ chains into a framework. TO4 mixed tetrahedral groups are located within the cavities of the framework. The structural formula of dokuchaevite can be represented as Cu2[Cu6O2](VO4)3Cl3.

Levantite, with the end-member formula KCa3(Al2Si3)O11(PO4), is the phosphate analogue of latiumite, KCa3(Al3Si2)O11(SO4, CO3) found in gehlenite–wollastonite hornfels on Har Parsa, Negev Desert, Israel. Levantite forms later zones on long-prismatic crystals of latiumite. Rarer homogeneous colourless levantite crystals up to 0.2 mm long and with mean composition (K0.94Ba0.01Na0.01□0.04)Σ1.00(Ca2.96Mg0.03)Σ2.99{(Si2.69Al2.06Fe3+0.16P0.06)Σ4.97O11}[(PO4)0.65(SO4)0.35]Σ1.00 were noted. Minerals of the levantite–latiumite series are associated with gehlenite, wollastonite, clinopyroxene of the esseneite–diopside series, anorthite and Ti-bearing andradite. Levantite crystalises in space group P21 with unit-cell parameters a = 12.1006(9) Å, b = 5.1103(4) Å, c = 10.8252(9) Å, β = 107.237(8)°, V = 639.34(9) Å3 and Z = 2. The structure of levantite is analogous to latiumite. It is formed by tetrahedral hybrid zweier double layers [(Si,Al)10O22] connected by Ca atoms. Three Ca atoms linked to different double layers are bridged over by (PO4) and minor (SO4) groups. K atoms reside in the cavities between two superimposed zweier double layers. The measured micro-indentation hardness of levantite gave VHN50 = 580(19) (mean of 14), range 550–611 kg/mm2, which correlates with 5 on the Mohs scale. Cleavage is good on (100). Twinning on (100) is polysynthetic or simple. The calculated density is 2.957 g cm–3. Levantite is optically negative with α = 1.608(2), β = 1.618(2), γ = 1.622(2) (λ = 589 nm), 2Vmeas. = 70(5)° and 2Vcalc. = 64.3°. Dispersion of the optical axes r > v is weak; the optical orientation is: Z = b, X ^ c = 22–27°; and it is non-pleochroic. Minerals of the levantite–latiumite series from Israel show characteristic Raman spectra with the main bands at 994 cm–1 [ν1(SO4)2–] and 945 cm–1 [ν1(PO4)3–]. The band intensity ν1(PO4)3–/ν1(SO4) ratio is well correlated with P and S contents in the investigated minerals. The strongest lines in the powder diffraction pattern [dobs, Å (I, %) (hkl)] are: 3.0762(100)(310), 2.8551(96)($\bar 2$13), 2.9704(92)($\bar 3$12), 2.8573(83)(013), 2.5552(66)(020), 2.8228(48)(212), 2.8893(40)(400), and 3.0634(30)(103).

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 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).

Three samples of halurgite were re-examined: two from the Chelkar salt dome in the North Caspian Region, Western Kazakhstan (the type locality and including the type specimen), and one from a new locality in the Satimola salt dome located in the same region. The crystal structure of halurgite has been solved for the first time on the specimen from Chelkar with the empirical formula Mg3.94[B8.03O13.03(OH)1.97]2·7.16H2O; refinement began with single-crystal X-ray diffraction data and was subsequently refined on a powder sample using the Rietveld method (Rp = 0.0232, Rwp = 0.0354 and Robs = 0.0558). The idealised crystal chemical formula of halurgite is Mg4[B8O13(OH)2]2·7H2O. The mineral is monoclinic, P2/c, a = 13.201(2), b = 7.5622(10), c = 13.185(2) Å, β = 91.834(14)°, V = 1315.6(4) Å3 and Z = 2. The crystal structure is unique. Eight B polyhedra form a fundamental building block [B8O16(OH)2], which is a six-membered borate ring (built by two pairs of B tetrahedra and two B triangles) with two additional triangular BO2(OH) groups. Each [B8O16(OH)2] ring is linked to six adjacent analogous rings to form a [B8O13(OH)2]∞ layer. These layers are connected via MgO6 and Mg(OH)2(H2O)4 octahedra into a microporous heteropolyhedral pseudo-framework. The crystal structure of halurgite can also be described in terms of an approach developed for heterophyllosilicates containing three-layer HOH modules, where HOH refers to an octahedral layer O sandwiched between two heteropolyhedral layers H. In halurgite the HOH module consists of two heteropolyhedral (BO3 triangles + BO4 tetrahedra) borate H layers [B8O13(OH)2]∞ and a central interrupted O layer composed of MgO6 octahedra, whereas a more voluminous Mg(OH)2(H2O)4 octahedral complex and additional H2O molecules are located between HOH modules. Halurgite and four related synthetic H-free borates M2Cd3B16O28 and M2Ca3B16O28 (M = Rb or Cs) can be considered microporous heterophylloborates.

Single crystals of synthetic reidite and natural radiation-damaged zircon from Okueyama, Japan were investigated using X-ray diffraction. The pressure-induced zircon–reidite transition is described by the twisting and translations of SiO4 tetrahedra with disappearance of the SiO4–ZrO8 shared edges. The lattice of radiation-damaged zircons expands mainly from α-decays of radioactive elements such as U and Th. Although old radiation-damaged zircons show anomolous lattice distortion, young radiation-damaged zircons do not show such distortions. These distortions are caused by thermal recovery that suppresses the Si4+–Zr4+ repulsion between the SiO4 tetrahedron and ZrO8 dodecahedron. These changes in structure can be understood by considering the cation–cation repulsion between the SiO4–ZrO8 shared edges.

We have investigated a diamond crystal that consists of several misorientated subgrains. The main feature of the crystal is the dark areas in the cathodoluminescent core that has ‘estuary-like’ boundaries extending along the subgrain interfaces. The core has >3100 ppm of nitrogen, and the share of the B form is >95%; the absorbance of the centre N3VH at 3107 cm–1 reaches 75 cm–1. The N3 centre absorbance, as well as N3 luminescence, is absent in the core. In the outer part of the crystal, bright blue luminescence of the N3 centre is apparent, and the N3 absorbance reaches 5.3 cm–1. These observations could be explained by the conversion of N3 centres to N3VH after attaching a hydrogen atom. After the full conversion of the N3 centres, the diamond becomes darker under CL. We hypothesise the dark core has a specific shape due to the post-growth diffusion of the hydrogen.

We describe the new species ognitite, NiBiTe, and a Co-rich variety of maucherite, hitherto unreported; both were discovered in the Ognit ultramafic complex of Neoproterozoic age in Eastern Sayans, Russia. The mean composition of ognitite (n = 7) is: Ni 17.05, Fe 0.07, Cu 0.14, Pd 0.14, Te 32.53, Bi 49.64, total 99.57 wt.%, corresponding to: (Ni1.11Cu0.008Fe0.005Pd0.005)Σ1.13Bi0.90Te0.97 (Σ atoms = 3 apfu). Ognitite is trigonal, space group P3m1 [R1 = 0.0276 for 81 reflections with Fo > 4σ(Fo)]. The unit-cell parameters derived from the single-crystal X-ray diffraction data are: a = 3.928(1) Å, c = 5.385(1) Å and V = 71.95(4) Å3, with Z = 1. The c:a ratio is 1.37. The powder X-ray diffraction data obtained on the same fragment used for the single-crystal study are: a = 3.9332(4) Å, c = 5.3920(6) Å and V = 72.24(1) Å3. Ognitite exhibits the brucite-type structure with edge-sharing NiTe3Bi3 octahedra forming sheets parallel to (0001). It is related to melonite, but is distinct compositionally by the extreme Bi-enrichment (melonite and its synthetic analogue contain <0.4 Bi apfu), and structurally as Bi and Te are ordered at two distinct sites, leading to the loss of the centre of symmetry in ognitite.

At more than 9 wt.% Co, or ~2 apfu Co, the core of Co-rich maucherite [(Ni,Co)11As8] in a zoned crystal, which is surrounded by Co-depleted orcelite, far surpasses the norm (≤1 and up to 3.9 wt.% Co). The unit-cell parameters of the Co-rich maucherite are: a = 6.85(2) and c = 21.83(5) Å, which are based on results of synchrotron micro-Laue diffraction.

The host rock consists of serpentine, clinochlore (Mg# 95–97) and skeletal chromite. We favour the metastable crystallisation of fluid-saturated globules of a sulfide–arsenide melt to explain the anomalous compositions of ore minerals at Ognit. These anomalies seem consistent with rapid cooling in a fluid-enriched system, possibly related to late-stage degassing of the magma, as reflected in a prominent metasomatic aureole at the contact with the enclosing gneissic rocks.

The new minerals camanchacaite, NaCaMg2[AsO4]2[AsO3(OH)2], chinchorroite, Na2Mg5(As2O7)2(AsO3OH)2(H2O)10, espadaite, Na4Ca3Mg2[AsO3(OH)]2[AsO2(OH)2]10(H2O)6·H2O, magnesiofluckite, CaMg(AsO3OH)2(H2O)2, picaite, NaCa[AsO3OH][AsO2(OH)2] and ríosecoite, Ca2Mg(AsO3OH)3(H2O)2, were discovered on two closely related specimens collected from the Torrecillas mine, Iquique Province, Chile. These minerals occur as secondary phases on massive quartz–hematite also in association with anhydrite, gypsum, halite and talmessite. Camanchacaite is monoclinic, C2/c, a = 12.470(9), b = 12.554(9), c = 6.848(9) Å, β = 113.75(2)°, V = 981.3(16) Å3 and Z = 4. It has a protonated alluaudite-type structure. Chinchorroite is triclinic, P$\bar{1}$, a = 8.7777(2), b = 8.8570(3), c = 9.7981(7) Å, α = 91.097(6), β = 110.544(8), γ = 103.167(7)°, V = 690.43(7) Å3 and Z = 1. The structure contains abbreviated chains of five edge-sharing Mg octahedra that are linked by pyroarsenate and hydrogen-arsenate groups. Espadaite is orthorhombic, Ccca, a = 12.3649(10), b = 22.181(2), c = 18.3292(13) Å, V = 5027.1(7) Å3 and Z = 4. The structure is based on heteropolyhedral sheets of formula {Ca3Mg2[AsO3(OH)]2[AsO2(OH)2]10}4− that contain large voids; NaO6 polyhedra occupy the interlayer region. Magnesiofluckite is triclinic, P$\bar{1}$, a = 8.4143(6), b = 7.5321(5), c = 6.8917(4) Å, α = 82.477(6), β = 97.682(6), γ = 95.379(6)°, V = 427.84(5) Å3 and Z = 2. It is isostructural with fluckite. Picaite is monoclinic, P21/c, a = 7.2474(4), b = 14.6547(7), c = 7.2624(5) Å, β = 99.520(7)°, V = 760.70(8) Å3 and Z = 4. The structure contains chains of edge-sharing Na− and Ca octahedra with bridging AsO3(OH) and AsO2(OH)2 tetrahedra. Ríosecoite is triclinic, P$\bar{1}$, a = 6.8110(9), b = 7.3156(12), c = 11.7773(17) Å, α = 83.466(6), β = 84.394(6), γ = 79.779(6)°, V = 571.95(15) Å3 and Z = 2. The structure contains tetramers of edge-sharing CaO7 and CaO8 polyhedra linked by MgO6 octahedra and bridging AsO3(OH) groups to form chains.

Ferrierite is the name for a series of zeolite-group of minerals which includes three species with the same ferrierite framework (FER) crystal structure but different extra-framework cations. Recent studies have shown that ferrierite can exhibit a fibrous-asbestiform crystal habit and may possess the same properties as carcinogenic fibrous erionite. Characterisation of the ferrierite in and around a mine location will be helpful in assessing the potential for toxic outcomes of exposure in the mine and any local population.

The zeolite-rich tuff deposit of Lovelock, Nevada, USA is the largest occurrence of diagenetic ferrierite-Mg. A previous survey reported that ferrierite hosted in these rocks displays a fibrous morphology. However, these observations concerned a limited number of samples and until now there has been little evidence of widespread occurrence of fibrous ferrierite in the Lovelock deposit.

The main goal of this study was to perform a mineralogical and morphometric characterisation of the tuff deposit at Lovelock and evaluate the distribution of fibrous ferrierite in the outcrop. For this purpose, a multi-analytical approach including powder X-ray diffraction, scanning and transmission microscopies, micro-Raman spectroscopy, thermal analyses, and surface-area determination was applied.

The results prove fibrous ferrierite is widespread and intermixed with mordenite and orthoclase, although there are variations in the spatial distribution in the bedrock. The crystal habit of the ferrierite ranges from prismatic to asbestiform (elongated, thin and slightly flexible) and fibres are aggregated in bundles. According to the WHO counting criteria, most of the ferrierite fibres can be classified as breathable. While waiting for confirmatory in vitro and in vivo tests to assess the actual toxicity/pathogenicity potential of this mineral fibre, it is recommended to adopt a precautionary approach for mining operations in this area to reduce the risk of exposure.

Schizolite, originating from the type locality, Tutop Agtakôrfia, in the Ilímaussaq alkaline complex, Julianehåb district, South Greenland, was described initially by Winther (1901) with additional data being supplied by Bøggild (1903). Recently, a proposal for the new mineral ‘marshallsussmanite’ was submitted to, and approved by, the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA2013-067) by Origlieri et al. (2013). Results from the detailed examination of two schizolite cotype samples presented here, using single-crystal and powder X-ray diffraction, and optical properties, confirms it to be equivalent to ‘marshallsussmanite’. Historical precedence sets a priority for discrediting the name ‘marshallsussmanite’ in favour of the original, more-than-a century-old name, schizolite. The two schizolite samples investigated vary slightly in physical and chemical properties but are consistent overall. The prismatic crystals are pale red or pink to brownish. Schizolite is brittle with a splintery aspect. It is biaxial (+), with average optical parameters: α = 1.626 ± 0.003, β = 1.630 ± 0.002, γ = 1.661 ± 0.002, 2Vmeas = 71(4)° and 2Vcalc = 40°; there is no pleochroism. Electron microprobe analysis shows both samples have nearly identical compositions (differences <0.4 wt.% oxide), with the mean values of: SiO2 52.6(4); Al2O3 0.005(1); FeO 2.54(2); MnO 13.86(9); CaO 17.9(4); Na2O 8.9(1); and H2O 2.59(2) wt.% oxide; this corresponds to a mean formula of: Na1.00(2)Ca1.11(7)Mn0.68(1)Fe0.12(0)Si3.041(1)O8(OH). Final least-squares structure refinements for both samples converged at R1 values ≤2.0%; H atoms were located in all refinements.

The new minerals cuatrocapaite-(NH4) (IMA2018-083) and cuatrocapaite-(K) (IMA2018-084) are the NH4- and K-dominant members of a series with the general formula (NH4,K)3(NaMg□)(As2O3)6Cl6·16H2O. Both minerals were found at the Torrecillas mine, Iquique Province, Chile, where they occur as secondary alteration phases. Both minerals occur as hexagonal tablets up to ~0.3 mm in diameter. They are transparent, with a vitreous lustre and white streak. For both, the Mohs hardness is ca. 2½, the crystals are somewhat flexible, but not elastic, the fracture is irregular and the cleavage is perfect on {001}. The measured densities are 2.65(2) and 2.76(2) g/cm3 for the NH4- and K-dominant species, respectively. Optically, cuatrocapaite-(NH4) is uniaxial (–) with ω = 1.779(3) and ε = 1.541(3) and cuatrocapaite-(K) is uniaxial (–) with ω = 1.777(3) and ε = 1.539(3) (white light). The minerals are insoluble in acids, but decompose in NaOH(aq). The empirical formulas, determined from electron-microprobe analyses, are (NH4)2.48Na1.66Mg0.87K0.09(As12O18.05)Cl5.88·16.02H2O and K2.68Na1.33Mg0.93(NH4)0.31(As12O18.01)Cl6.16·16.04H2O. The minerals are trigonal, space group R${\bar 3}$m; the cuatrocapaite-(NH4) cell parameters are a = 5.25321(19), c = 46.6882(19) Å, V = 1115.80(9) Å3 and Z = 1; the cuatrocapaite-(K) cell parameters are a = 5.2637(15), c = 46.228(8) Å, V = 1109.2(7) Å3 and Z = 1. The structures, refined for cuatrocapaite-(NH4) to R1 = 1.78% for 544 Io > 2σI reflections, contain four types of layers: (1) a planar neutral As2O3 (arsenite) sheet; (2) an (${\rm NH}_{\rm 4}^{\vskip -2pt\rm \scale65% +} $,K+) layer that links adjacent arsenite sheets; (3) a Cl– layer placed on the As side of each arsenite; and (4) a layer containing partially occupied Na, Mg and H2O sites that is flanked on either side by Cl layers. The layer sequence for the type 1, 2 and 3 layers is identical to the Cl–As2O3–K–As2O3–Cl layer sequence in the structures of lucabindiite and gajardoite.

We present an assessment of the thermo-elastic behaviour of rutile based on X-ray diffraction data and direct elastic measurements available in the literature. The data confirms that the quasi-harmonic approximation is not valid for rutile because rutile exhibits substantial anisotropic thermal pressure, meaning that the unit-cell parameters change significantly along isochors. Simultaneous fitting of both the diffraction and elasticity data yields parameters of KTR0= 205.14(15) GPa, KSR0= 207.30(14) GPa, $K_{TR0}^{\prime} $= 6.9(4) in a 3rd-order Birch-Murnaghan Equation of State for compression, αV0= 2.526(16) × 10–5 K–1, Einstein temperature θE = 328(12) K, Anderson-Grüneisen parameter δT = 7.6(6), with a fixed thermal Grüneisen parameter γ = 1.4 to describe the thermal expansion and variation of bulk modulus with temperature at room pressure. This Equation of State fits all of the available data up to 7.3 GPa at room temperature, and up to 1100 K at room pressure within its uncertainties. We also present a series of formulations and a simple protocol to obtain thermodynamically consistent Equations of State for the volume and the unit-cell parameters for stiff materials, such as rutile. In combination with published data for garnets, the Equation of State for rutile indicates that rutile inclusions trapped inside garnets in metamorphic rocks should exhibit negative residual pressures when measured at room conditions.