New arsenate minerals from the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. XV. Calciojohillerite, NaCaMgMg2(AsO4)3, a member of the alluaudite group

The new alluaudite-group mineral calciojohillerite is one of the major arsenates in sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. In middle zones of the fumarole, calciojohillerite is associated with hematite, tenorite, johillerite, nickenichite, bradaczekite, badalovite, tilasite, lammerite, ericlaxmanite, aphthitalite-group sulfates, langbeinite, calciolangbeinite, anhydrite, sanidine, fluorophlogopite, fluoborite, cassiterite, pseudobrookite, rutile, sylvite and halite. In deep zones it occurs in association with anhydrite, diopside, hematite, svabite, berzeliite, schäferite, forsterite, magnesioferrite, ludwigite, rhabdoborite-group fluoroborates, powellite, baryte, fluorapatite, udinaite, arsenudinaite and paraberzeliite. Calciojohillerite forms prismatic crystals up to 1 cm long, their aggregates and crystal crusts up to 0.5 m2. It is transparent, colourless, pale green, pale yellow, light blue, pale lilac or pink, with vitreous lustre. The mineral is brittle, with imperfect cleavage. The Mohs hardness is 3½. Dcalc is 3.915 g cm–3. Calciojohillerite is optically biaxial (–), α = 1.719(3), β = γ = 1.732(3); 2Vmeas. = 15(10)°. Chemical composition (wt.%, electron-microprobe; holotype) is: Na2O 7.32, K2O 0.10, CaO 6.82, MgO 20.31, MnO 0.68, CuO 0.27, ZnO 0.02, Al2O3 0.56, Fe2O3 3.53, TiO2 0.01, SiO2 0.03, P2O5 1.25, V2O5 0.10, As2O5 58.77, SO3 0.13, total 99.90. The empirical formula based on 12 O atoms is (Na1.30K0.01Ca0.67Mg2.78Mn0.05Cu0.02Al0.06Fe3+0.24)Σ5.13(As2.83P0.10S0.01V0.01)Σ2.95O12. Calciojohillerite is monoclinic, C2/c, a = 11.8405(3), b = 12.7836(2), c = 6.69165(16) Å, β = 112.425(3)°, V = 936.29(4) Å3 and Z = 4. The crystal structure was solved from single-crystal X-ray diffraction data, R1 = 0.0227. Calciojohillerite is isostructural with other alluaudite-group minerals. Its simplified crystal chemical formula is A (1)Ca A (1)′□ A (2)□ A (2)′Na M (1)Mg M (2)Mg2(AsO4)3 (□ = vacancy). The idealised formula is NaCaMg3(AsO4)3, or, according to the nomenclature of alluaudite-group arsenates, NaCaMgMg2(AsO4)3. Calciojohillerite is named as an analogue of johillerite NaCu2+MgMg2(AsO4)3 with species-defining Ca instead of Cu in the ideal formula.

Crystal-chemistry of micas belonging to the yangzhumingite-fluorophlogopite and phlogopite-fluorophlogopite series from the Apuan Alps (northern Tuscany, Italy)

The present work reports the crystal-chemical characterization of micas from the Monte Arsiccio and Buca della Vena mines (Apuan Alps, Italy) through electron microprobe analysis, single-crystal X-ray diffraction, and Raman spectroscopy. The sample from the Monte Arsiccio mine can be classified as an intermediate member of the yangzhumingite-fluorophlogopite series, with average crystal-chemical formula (K0.85Na0.01Ba0.09)Σ=0.95(Mg2.11Fe2+0.23Fe3+0.11Cr3+0.01Al0.20Ti0.04☐0.30)Σ=3.00(Si3.20Al0.80)Σ=4.00O10.00F1.90Cl0.02(OH)0.08. Unit-cell parameters are a ~ 5.30, b ~ 9.18, c ~ 10.14 Å, β ~ 100.12°, V ~ 486.22 Å3, corresponding to the 1M polytype. Structure refinements, performed in C2/m space group, converged to R1 = 3.54 and 4.46% and provided Mg plus Fe occupancy in the range 86–94% for the octahedral M1 and M2 sites. Raman spectroscopy shows very weak bands in the OH stretching region at ~ 3690 and 3580 cm−1. The sample from the Buca della Vena mine has been identified as an (OH)-rich fluorophlogopite, with average crystal-chemical formula (K0.84Na0.02Ca0.01)Σ=0.87(Mg2.12Fe2+0.55Fe3+0.10Al0.18☐0.05)Σ=3.00(Si2.99Al1.01)Σ=4.00O10.00F1.02Cl0.09(OH)0.89. Its unit-cell parameters are a ~ 5.33, b ~ 9.22, c ~ 10.23 Å, β ~ 100.09°, V ~ 494.39 Å3. Structure refinements gave good R1 values (3.27 and 4.37%) and revealed octahedral occupancy of 82–84% Mg and 16–18% Fe. Strong Raman signals at ~ 3702 cm−1 and 3595 cm−1 were observed in the OH stretching region. The findings allow to better understand not only the mineralogy of the Apuan Alps but, more generally, the crystal chemical details of intermediate dioctahedral-trioctahedral mica belonging to the yanzhumingite-fluorophlogopite series.

Vittinkiite, MnMn4[Si5O15], a member of the rhodonite group with a long history: definition as a mineral species

The rhodonite-group mineral with the idealised, end-member formula MnMn4[Si5O15] and the crystal chemical formula VIIM(5)MnVIM(1–3)Mn3VIIM(4)Mn[Si5O15] (Roman numerals indicate coordination numbers) is defined as a valid mineral species named vittinkiite after the type locality Vittinki (Vittinge) mines, Isokyrö, Western and Inner Finland Region, Finland. Vittinkiite is an isostructural analogue of rhodonite, ideally CaMn4[Si5O15], with Mn2+ > Ca at the M(5) site. Besides Vittinki, vitiinkiite was found in more than a dozen rhodonite deposits worldwide, however, it is significantly less common in comparison with rhodonite. The mineral typically forms pink to light pink massive, granular aggregates and is associated with quartz, rhodonite, tephroite, pyroxmangite and Mn oxides. Vittinkiite is optically biaxial (+), with α = 1.725(4), β = 1.733(4), γ = 1.745(5) and 2Vmeas = 75(10)° (589 nm). The chemical composition of the holotype (wt.%, electron microprobe) is: MgO 0.52, CaO, 0.93, MnO 51.82, FeO 1.26, ZnO 0.11, SiO2 46.48, total 101.12. The empirical formula calculated based on 15 O apfu is Mn4.71Ca0.11Fe0.11Mg0.08Zn0.01Si4.99O15. Vittinkiite is triclinic, space group P $\bar{1}$ , with a = 6.6980(3), b = 7.6203(3), c = 11.8473(5) Å, α = 105.663(3), β = 92.400(3), γ = 94.309(3)°, V = 579.38(7) Å3 and Z = 2. The crystal structure is solved on a single crystal to R1 = 3.85%. Polymorphism of MnSiO3 (rhodonite-, pyroxmangite-, garnet- and clinopyroxene-type manganese metasilicates) is discussed, as well as the relationship between vittinkiite and pyroxmangite, ideally Mn7[Si7O21], and the application of infrared spectroscopy for the identification of manganese pyroxenoids.

Al analogue of chayesite from a lamproite of Cancarix, SE Spain, and its crystal structure

Al analogue of chayesite (with Al > Fe3+) was found in a lamproite from Cancarix, SE Spain. The mineral forms green thick-tabular crystals up to 0.4 mm across in cavities. The empirical formula derived from EMP measurements and calculated on the basis of 17 Mg + Fe + Al + Si apfu is (K0.75 Na0.20 Ca0.11)Mg3.04 Fe0.99 Al1.18 Si11.80 O30. The crystal structure was determined from single crystal X-ray diffraction data ( R = 2.38%). The mineral is hexagonal, space group P 6/ mcc, a = 10.09199(12), c = 14.35079(19) Å, V = 1265.78(3) Å3, Z = 2. Fe is predominantly divalent. Al is mainly distributed between the octahedral A site and the tetrahedral T 2 site. The crystal chemical formula derived from the structure refinement is C (K0.73 Na0.16 Ca0.11)B (Na0.02)4 A(Mg0.42 Al0.29 Fe0.29)2 T 2(Mg0.71 Fe0.16 Al0.13)3 T 1(Si0.985 Al0.015)12 O30.

Petrovite, Na10CaCu2(SO4)8, a new fumarolic sulfate from the Great Tolbachik fissure eruption, Kamchatka Peninsula, Russia

Petrovite, Na10CaCu2(SO4)8, is a new sulfate mineral discovered on the Second scoria cone of the Great Tolbachik fissure eruption. The mineral occurs as globular aggregates of tabular crystals up to 0.2 mm in maximal dimension, generally with gaseous inclusions. The empirical formula calculated on the basis of O = 32 is Na6(Na1.80K0.20)Σ2Na(Ca0.82Na0.06Mg0.02)Σ0.90(Cu1.84Mg0.16)Σ2(Na0.52□0.48)Σ1S8.12O32. The crystal-chemical formula is CuNa6−2xCax(SO4)4, which, for x ≈ 0.5, results in the idealised formula Na10CaCu2(SO4)8. The crystal structure of petrovite was determined using single-crystal X-ray diffraction data; the space group is P21/c, a = 12.6346(8), b = 9.0760(6), c = 12.7560(8) Å, β = 108.75(9)°, V = 1385.1(3) Å3, Z = 2 and R1 = 0.051. There are one Cu and six Na sites, one of which is also occupied by the essential amount of Ca. The Cu atom forms five Cu–O bonds in the range 1.980–2.180 Å and two long bonds ≈ 2.9 Å resulting in the formation of the CuO7 polyhedra, which share corners with SO4 tetrahedra to form isolated [Cu2(SO4)8]12− clusters. The clusters are surrounded by Na sites, which provide their linkage into a three-dimensional framework. The Mohs’ hardness is 4. The mineral is biaxial (+), with α = 1.498(3), βcalc = 1.500, γ = 1.516(3) and 2V = 20(10) (λ = 589 nm). The seven strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 7.21(27)(110); 6.25(38)(102); 4.47(31)(212); 3.95(21)(30$\bar{2}$); 3.85(17)(121); 3.70(36)(202); and 3.65(34)(22$\bar{1}$). The mineral is named in honour of Prof Dr Tomas Georgievich Petrov (b. 1931) for his contributions to mineralogy and crystallography and, in particular, for the development of technology for the industrial fabrication of jewellery malachite.

New arsenate minerals from the Arsenatnaya fumarole, Tolbachik volcano, Kamchatka, Russia. XIV. Badalovite, NaNaMg(MgFe3+)(AsO4)3, a member of the alluaudite group

The new alluaudite-group mineral badalovite 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 hematite, tenorite, cassiterite, johillerite, nickenichite, calciojohillerite, bradaczekite, metathénardite, aphthitalite, langbeinite, calciolangbeinite, sanidine, fluorophlogopite, fluoborite, tilasite, anhydrite, pseudobrookite, sylvite, halite, lammerite, urusovite, ericlaxmanite, arsmirandite, svabite, krasheninnikovite, euchlorine, wulffite and alumoklyuchevskite. Badalovite forms oblique-angled prismatic crystals up to 1 mm × 1 mm × 5 mm, typically combined in groups or crusts up to several hundred cm2 in area. The mineral is transparent, green, grey, yellow or colourless, with vitreous lustre. It is brittle, the Mohs hardness is 3½. Cleavage was not observed, the fracture is uneven. Dcalc is 4.02 g cm–3. Badalovite is optically biaxial (–), α = 1.753(3), β = 1.757(3), γ = 1.758(3) and 2Vmeas. = 50(10)°. Chemical composition (wt.%, electron-microprobe; holotype) is: Na2O 9.23, K2O 0.19, CaO 2.04, MgO 13.78, MnO 0.31, CuO 0.12, ZnO 0.24, Al2O3 0.06, Fe2O3 12.77, TiO2 0.01, SiO2 0.06, P2O5 0.33, V2O5 0.05, As2O5 61.51, SO3 0.02, total 100.72. The empirical formula based on 12 O apfu is Na1.67Ca0.20K0.02Mg1.92Zn0.02Mn0.02Cu0.01Fe3+0.90Al0.01(As3.01P0.03Si0.01)Σ3.05O12. The simplified formula is Na2Mg2Fe3+(AsO4)3. Badalovite is monoclinic, C2/c, a = 11.9034(3), b = 12.7832(2), c = 6.66340(16) Å, β = 112.523(3)°, V = 936.59(4) Å3 and Z = 4. The strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 6.41(38)(020), 5.505(20)(200), 3.577(23)($\bar{1}$31), 3.523(25)(310), 3.211(46)($\bar{1}$12), 2.911(28)($\bar{2}$22, $\bar{3}$12), 2.765(100)(240, 400) and 2.618(26)($\bar{1}$32). The crystal structure was solved from single-crystal XRD data with an R1 of = 2.49%. Badalovite is isostructural with other alluaudite-group minerals. Its simplified crystal chemical formula is A(1)NaA(1)’□A(2) □A(2)’NaM(1)MgM(2)(Mg0.5Fe3+0.5)2(AsO4)3 (□ – vacancy) and the end-member formula is NaNaMg(MgFe3+)(AsO4)3. The mineral is named in honour of the outstanding mineralogist and geochemist Stepan Tigranovich Badalov (1919–2014).

A Plethora of Epigenetic Minerals Reveals a Multistage Metasomatic Overprint of a Mantle Orthopyroxenite from the Udachnaya Kimberlite

More than forty mineral species of epigenetic origin have been identified in an orthopyroxenite from the Udachnaya-East kimberlite pipe, Daldyn kimberlite field, Siberian platform. Epigenetic phases occur as: (1) Mineral inclusions in the rock-forming enstatite, (2) daughter minerals within large (up to 2 mm) crystallized melt inclusions (CMI) in the rock-forming enstatite, and (3) individual grains and intergrowths in the intergranular space of the xenolith. The studied minerals include silicates (olivine, clinopyroxene, phlogopite, tetraferriphlogopite, amphibole-supergroup minerals, serpentine-group minerals, talc), oxides (several generations of ilmenite and spinel, rutile, perovskite, rare titanates of the crichtonite, magnetoplumbite and hollandite groups), carbonates (calcite, dolomite), sulfides (pentlandite, djerfisherite, pyrrhotite), sulfate (barite), phosphates (apatite and phosphate with a suggested crystal-chemical formula Na2BaMg[PO4]2), oxyhydroxide (goethite), and hydroxyhalides (kuliginite, iowaite). The examined epigenetic minerals are interpreted to have crystallized at different time spans after the formation of the host rock. The genesis of minerals is ascribed to a series of processes metasomatically superimposed onto the orthopyroxenite, i.e., deep-seated mantle metasomatism, infiltration of a kimberlite-related melt and late post-emplacement hydrothermal alterations. The reaction of orthopyroxene with the kimberlite-related melt has led to orthopyroxene dissolution and formation of the CMI, the latter being surrounded by complex reaction zones and containing zoned olivine grains with extremely high-Mg# (up to 99) cores. This report highlights the utility of minerals present in minor volume proportions in deciphering the evolution and modification of mantle fragments sampled by kimberlitic and other deep-sourced magmas. The obtained results further imply that the whole-rock geochemical analyses of mantle-derived samples should be treated with care due to possible drastic contaminations from “hiding” minor phases of epigenetic origin.

Adding complexity to the garnet supergroup: monteneveite, Ca₃Sb⁵⁺₂(Fe³⁺₂Fe²⁺)O₁₂, a new mineral from the Monteneve mine, Bolzano Province, Italy

Monteneveite, ideally Ca3Sb25+(Fe23+Fe2+)O12, is a new member of the garnet supergroup (IMA 2018-060). The mineral was discovered in a small specimen belonging to the Swedish Museum of Natural History coming from the now abandoned Monteneve Pb–Zn mine in Passiria Valley, Bolzano Province, Alto Adige (South Tyrol), Italy. The specimen consists of mainly magnetite, sphalerite, tetrahedrite-(Fe) and oxycalcioroméite. Monteneveite occurs as black, subhedral crystals with adamantine lustre. They are equidimensional and up to 400 µm in size, with a subconchoidal fracture. Monteneveite is opaque, grey in reflected light, and isotropic under crossed polars. Measured reflectance values (%) at the four COM wavelengths are 12.6 (470 nm), 12.0 (546 nm), 11.6 (589 nm) and 11.4 (650 nm). The Vickers hardness (VHN100) is 1141 kg mm−2, corresponding to H=6.5–7, and the calculated density is 4.72(1) g cm−3. A mean of 10 electron microprobe analyses gave (wt %) CaO 23.67, FeO 3.75, Fe2O3 29.54, Sb2O5 39.81, SnO2 2.22, ZnO 2.29, MgO 0.15, MnO 0.03 and CoO 0.03. The crystal chemical formula calculated on the basis of a total of eight cations and 12 anions, and taking into account the available structural and spectroscopic data, is (Ca2.97Mg0.03)Σ=3.00 (Sb1.735+Sn0.104+Fe0.173+)Σ=2.00(Fe2.433+Fe0.372+Zn0.20)Σ=3.00O12. The most significant chemical variations encountered in the sample are related to a substitution of the type YSn4++ZFe3+→YSb5++ZFe2+. Mössbauer data obtained at RT and 77 K indicate the presence of tetrahedrally coordinated Fe2+. Raman spectroscopy demonstrates that there is no measurable hydrogarnet component in monteneveite. The six strongest Bragg peaks in the powder X-ray diffraction pattern are [d (Å), I (%), (hkl)]: 4.45, 100, (220); 3.147, 60, (400); 2.814, 40, (420); 2.571, 80, (422); 1.993, 40, (620); 1.683, 60, (642). Monteneveite is cubic, space group Ia-3‾d, with a=12.6093(2) Å, V=2004.8(1) Å3, and Z=8. The crystal structure was refined up to R1=0.0197 for 305 reflections with Fo>4σ(Fo) and 19 parameters. Monteneveite is related to the other Ca-, Sb- and Fe-bearing, nominally Si-free members of the bitikleite group, but it differs in that it is the only known garnet species with mixed trivalent and divalent cations (2:1) at the tetrahedral Z site. Textural and mineralogical evidence suggests that monteneveite formed during peak metamorphism (at ca. 600 ∘C) during partial breakdown of tetrahedrite-(Fe) by reactions with carbonate, under relatively oxidizing conditions. The mineral is named after the type locality, the Monteneve (Schneeberg) mine.

Raman Spectroscopy and Single-Crystal High-Temperature Investigations of Bentorite, Ca6Cr2(SO4)3(OH)12·26H2O

The crystal structure of bentorite, ideally Ca6Cr2(SO4)3(OH)12·26H2O, a Cr3+ analogue of ettringite, is for the first time investigated using X-ray single crystal diffraction. Bentorite crystals of suitable quality were found in the Arad Stone Quarry within the pyrometamorphic rock of the Hatrurim Complex (Mottled Zone). The preliminary semi-quantitative data on the bentorite composition obtained by SEM-EDS show that the average Cr/(Cr + Al) ratio of this sample is >0.8. Bentorite crystallizes in space group P31c, with a = b = 11.1927(5) Å, c =21.7121(10) Å, V = 2355.60(18) Å3, and Z = 2. The crystal structure is refined, including the hydrogen atom positions, to an agreement index R1 = 3.88%. The bentorite crystal chemical formula is Ca6(Cr1.613Al0.387)Σ2[(SO4)2.750(CO3)0.499]Σ3.249(OH)11.502·~25.75H2O. The Raman spectra of bentorite from two different localities exhibit the presence of the main stretching and bending vibrations related to the sulfate group at 983 cm−1 (ν1), 1109 cm−1 (ν3), 442 cm−1 (ν2), and 601 cm−1 (ν4). Moreover, the presence of bands assigned to the symmetric Cr(OH)63− stretching mode and hydroxyl deformation vibrations of Cr–OH units at ~540 cm−1 and ~757 cm−1, respectively, may be used to distinguish between ettringite and bentorite. In situ high temperature single crystal XRD experiments show that the decomposition of bentorite starts at ca. 45 °C and that a dehydroxylation product similar to metaettringite is formed.

Thermoelasticity, cation exchange, and deprotonation in Fe-rich holmquistite: Toward a crystal-chemical model for the high-temperature behavior of orthorhombic amphiboles

The thermoelastic behavior of a crystal of Fe-rich holmquistite with crystal-chemical formula A(K0.01Na0.01)B(Li1.88Mg0.10Na0.02)C(Mg1.68Fe1.422+Mn0.022+Al1.88)TSi8.00O22W[(OH)1.97F0.03] was studied by single-crystal X-ray diffraction at temperatures up to 1023 K, where isothermal annealing in air for 160 h yielded the loss of 0.85 H apfu coupled with oxidation of M1Fe. A complex pattern of cation exchanges was deciphered by comparing structure refinements done before and after annealing. Li migration from the M4 to M3 site is responsible for nonlinearity of the c parameter around 600 K during the first annealing. Cooling of the partially deprotonated crystal to room temperature (RT) showed discontinuities in trends of the b and c parameters around 820–800 K, which cannot be ascribed to a phase transition and can be explained by a rearrangement of the structural units affecting the geometry of the M4 polyhedron. Such discontinuities have never been observed in amphiboles before and must be related to dimensional constraints deriving from the peculiar composition of this amphibole, which contains the smallest possible homovalent constituents, i.e., BLi, CAl, and TSi. The calculated thermo-elastic parameters are: Fe-rich holmquistite: αa = 1.36(2)×10–5; αb = 0.55(1)×10–5; αc = 1.5(1)×10–5 – 6.7(9)×10–9; αV = 3.5(3)×10–5 – 0.8(3)×10–8 (polynomial); 2.58(6)×10–5 (linear); partially deprotonated Fe-rich holmquistite: αa = 1.324(9)×10–5 (RT-1023 K); αb = 0.60(1)×10–5 (RT-773 K); αc = 0.68(2)×10–5 (RT-773 K); αV = 2.59(2)×10–5 (RT-773 K). Fe-rich holmquistite is much stiffer than all the previously studied orthorhombic Pnma and Pnmn amphiboles. The results of this work allow progress toward a general model that may explain how the amphibole structure responds to non-ambient conditions, and allows the release of water in diverse geological environments.