High-pressure,high-temperature stability of surinamite in the system MgO-BeO-Al2O3-SiO2-H2O

The MgAl surinamite end member, (Mg₃Al₃)^[6]O[AlBeSi₃O₁₅], was synthesized in the requisite system with and without water. The new phase is monoclinic, space group P2/n, with a=9.881(1)Å; b=11.311(1) Å; c=9.593(1) Å; =109.52(2)°. Refractive indices are n _x=1.7015(20); n _y=1.7035(20); n _z=1.7055(20). The infrared spectrum shows characteristic differences against the structurally related and optically extremely similar phase sapphirine.Using the seeding technique, the preliminary stability field for MgAl surinamite was found to lie at high temperatures (650 °C) and high pressures (4 kbar). At lower temperatures breakdown takes place to hydrous assemblages of chlorite, talc, and chrysoberyl with kyanite or yoderite; at lower pressures chrysoberyl forms parageneses with sapphirine and cordierite. In crystal chemical terms the underlying principle for the stability of surinamite versus that of the low-pressure assemblages is the higher proportion of octahedrally coordinated Al in surinamite (75%). Following the same principle surinamite itself decomposes at still higher pressures to a paragenesis, in which all Al enters octahedral coordination (pyrope+a chrysoberyl-type phase and some unidentified X-ray peaks).The stability field of synthetic MgAl surinamite is in good agreement with P, T-estimates of some 8–12 kbar, 800°–950° C as taken from the literature for the few occurrences of natural, Fe-bearing surinamite in granulite and upper amphibolite facies environments. The incorporation of iron in surinamite must be limited, because this mineral is known to coexist with its more iron-rich breakdown assemblage almandine-rich garnet+chrysoberyl. As the minimum melting curve of granite under hydrous conditions lies outside the surinamite field up to a water pressure of about 20 kbar, the absence of surinamite in normal granitic pegmatites can already be explained by physical constraints. However, there are probably also chemical constraints in the generally high Fe/Mg bulk chemistry of the pegmatite environments.Now at Institut für Kristallographie, Technische Hochschule, Templergraben 55, D-5100 Aachen, FRG     

Magnesioneptunite, KNa2Li(Mg,Fe)2Ti2Si8O24, a new mineral species of the neptunite group

A new mineral of the neptunite group, magnesioneptunite KNa₂Li(Mg,Fe)₂Ti2Si₈O₂₄, a Mg-dominant analogue of neptunite and manganoneptunite, has been found in the Upper Chegem caldera near Mount Lakargi, Kabardino-Balkaria, the North Caucasus, Russia in a xenolith of altered sandstone located between skarnified carbonate xenoliths and ignimbrite. Magnesioneptunite occurs as nearly isometric grains and aggregates up to 0.1 mm in size in the cores of some grains of a Mg-rich variety of neptunite with Mg/(Fe + Mn) = 0.7?1.0. The chemical composition of magnesioneptunite with a maximum Mg content is as follows, wt %: 3.63 K₂O, 8.21 Na₂O, 1.73 Li₂O, 6.47 MgO, 0.04 MnO, 5.87 FeO, 0.07 Al₂O₃, 18.73 TiO₂, 56.88 SiO₂, 99.62 in total. The empirical formula is (K_0.67Na_0.32Ca_0.01)_Σ1.00Na_2.06Li_1.00 · (Mg_1.39Fe _0.71 ²⁺ )_Σ2.10(Si_7.90Al_0.01)_Σ7.91O₂₄. Grains of magnesioneptunite are dark brown to red-brown, translucent, with vitreous luster. D _calc = 3.15 g/cm³, and the Mohs hardness is 5–6. Cleavage parallel to the (110) is perfect. The new mineral is optically biaxial, positive, α = 1.697(2), β = 1.708 (3), γ = 1.725(3), 2V _meas = 45(15)°. The mineral is associated with quartz, alkali feldspar, rutile, aegirine, and neptunite. Magnesioneptunite and the Mg-rich variety of neptunite were formed as products of ilmenite alteration. Magnesioneptunite is monoclinic, C2/c; unit-cell parameters: a = 16.327(7), b = 12.4788(4), c = 9.9666(4) Å, β = 115.6519(5)°, V = 1830.5(1) ų, Z = 4. The type specimen is deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow.     

Perrierite-(La), (La,Ce,Ca)4(Fe2+,Mn)(Ti,Fe3+,Al)4(Si2O7)2O8, a new mineral species from the Eifel volcanic district, Germany

Non-metamict perrierite-(La) discovered in the Dellen pumice quarry, near Mendig, in the Eifel volcanic district, Rheinland-Pfalz, Germany has been approved as a new mineral species (IMA no. 2010-089). The mineral was found in the late assemblage of sanidine, phlogopite, pyrophanite, zirconolite, members of the jacobsite-magnetite series, fluorcalciopyrochlore, and zircon. Perrierite-(La) occurs as isolated prismatic crystals up to 0.5 × 1 mm in size within cavities in sanidinite. The new mineral is black with brown streak; it is brittle, with the Mohs hardness of 6 and distinct cleavage parallel to (001). The calculated density is 4.791 g/cm³. The IR spectrum does not contain absorption bands that correspond to H₂O and OH groups. Perrierite-(La) is biaxial (-), α = 1.94(1), β = 2.020(15), γ = 2.040(15), 2V _meas = 50(10)°, 2V _calc = 51°. The chemical composition (electron microprobe, average of seven point analyses, the Fe²⁺/Fe³⁺ ratio determined from the X-ray structural data, wt %) is as follows: 3.26 CaO, 22.92 La₂O₃, 19.64 Ce₂O₃, 0.83 Pr₂O₂, 2.09 Nd₂O₃, 0.25 MgO, 2.25 MnO, 3.16 FeO, 5.28 Fe₂O₃, 2.59 Al₂O₃, 16.13 TiO₂, 0.75 Nb₂O₅, and 20.06 SiO₂, total is 99.21. The empirical formula is (La_1.70Ce_1.45Nd_0.15Pr_0.06Ca_0.70)_Σ4.06(Fe _0.53 ²⁺ Mn_0.38Mg_0.08)_Σ0.99(Ti_2.44Fe _0.80 ³⁺ Al_0.62Nb_0.07)_Σ3.93Si_4.04O₂₂. The simplified formula is (La,Ce,Ca)₄(Fe²⁺,Mn)(Ti,Fe³⁺,Al)₄(Si₂O₇)₂O₈. The crystal structure was determined by a single crystal. Perrierite-(La) is monoclinic, space group P2₁/a, and the unit-cell dimensions are as follows: a =13.668(1), b = 5.6601(6), c = 11.743(1) Å, β = 113.64(1)°; V = 832.2(2) ų, Z = 2. The strong reflections in the X-ray powder diffraction pattern are [d, Å (I, %) (hkl)]: 5.19 (40) (110), 3.53 (40) ( $\overline 3 $ 11), 2.96 (100) ( $\overline 3 $ 13, 311), 2.80 (50) (020), 2.14 (50) ( $\overline 4 $ 22, $\overline 3 $ 15, 313), 1.947 (50) (024, 223), 1.657 (40) ( $\overline 4 $ 07, $\overline 4 $ 33, 331). The holotype specimen of perrierite-(La) is deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, with the registration number 4059/1.     

Mg4Ga8Ge2O20: A new synthetic analog of the mineral sapphirine

A new sapphirine-analog, Mg₄Ga₈Ge₂O₂₀, has been identified and characterized in the system MgO-Ga₂O₃-GeO₂ in samples quenched from 1400° C, 1 atm. It crystallizes with a triclinic unit-cell and is isostructural with the mineral sapphirine-1Tc, Mg₄Al₈Si₂O₂₀. It is stable over a broad range of stoichiometry associated with the exchange reaction 2 Ga³⁺ = Mg²⁺ }+Ge⁴⁺. TEM examination shows the common occurrence of polysynthetic twinning and suggests the existence of a high-temperature triclinic→monoclinic transition. The observation of sapphirine/spinel intergrowths is consistent with the structural relationships described previously.     

Structure and crystal chemistry of hydrous wadsleyite, Mg1.75SiH0.5O4: possible hydrous magnesium silicate in the mantle transition zone

The crystal structure of hydrous wadsleyite, Mg_1.75SiH_0.5O₄ synthesized in an MA 8-type apparatus at conditions of 1300°C and 15.5 GPa, has been analyzed and refined in space group Imma, using the X-ray intensities measured on a 60X60X10 μm single crystal. The composition (Z=8) and unit cell are Mg_1.74Si_0.97H_0.65O₄ by E.P.M.A. analysis and a=5.663(1) Å, b= 11.546(2) Å, c=8.247(4) Å, V=539.2(5) ų. The partial M-site occupancies were determined; vacancies associated with the incorporation of water are strongly concentrated on the Mg 3 site. The OH in the structure was confirmed by Raman and FTIR spectroscopies. The result of valence sum calculation based on the refined bond lengths indicates that O1 is a hydroxyl. The formula of hydrous wadsleyite can be expressed as Mg_2-xSiH_2xO₄, where 0≤x≤0.25. When x=0.25, all of the O1 site is hydroxyl and the maximum solubility of 3.3 wt% H₂O is realized. Structural relations to other dense hydrous phases are discussed.     

Structural characterisation of the high-pressure phase CaAl4Si2O11

Single crystals of CaAl₄Si₂O₁₁ were synthesised at 1,500?°C and 14 GPa in a multi-anvil press, and the structure of the phase determined by single-crystal X-ray diffraction at room conditions. The structure-type is that of the “hexagonal barium ferrites”. The space group of the average structure is P6 ₃ /mmc and the cell parameters are a?=?5.4223(4) Å, c?=?12.7041(6) Å, V?=?323.28(5) ų, with Z?=?2, and its density is 3.905?g?cm^?3, which is reasonable for a high-pressure alumino-silicate phase. The 22 oxygen and two calcium atoms within the unit-cell form an approximate hexagonal-close-packed array. Ten of the twelve octahedral interstices within this array that have only oxygen atoms for apices are filled with Si and/or Al. M1 octahedra share edges to form a spinel-like sheet of octahedra. The average bond length ?=?1.833 Å suggests mixed occupancy by Si and Al. The M1 octahedral sheets are linked by shared corners to pairs of face-sharing M2 octahedra containing Al, with ?= 1.918 Å. The remaining two cations of the unit-cell contents statistically occupy four tetrahedrally-coordinated interstices, which occur as face-sharing pairs. The average bond length for these sites (1.742 Å) suggests that they are occupied by Al, although Si occupancy cannot be excluded by the data. It is proposed that only one interstice of each pair is locally occupied, with the possibility of some short-range ordering of such occupancies. Complete long-range order leading to the acentric space group P6 ₃ mc is excluded by the data, as is the possibility of the average structure being comprised of merohedral (0?0?0?1) twins of P6 ₃ mc symmetry.     

Mariinskite, BeCr2O4, a new mineral, chromium analog of chrysoberyl

A new mineral, mariinskite, BeCr₂O₄, the chromium analog of chrysoberyl, has been found at the Mariinsky (Malyshevo) deposit, the Ural Emerald Mines, the Central Urals, Russia. The mineral is named after its type locality. It was discovered in chromitite in association with fluorphlogopite, Cr-bearing muscovite, eskolaite, and tourmaline. Mariinskite occurs as anhedral grains ranging from 0.01 to 0.3 mm in size; in some cases it forms pseudohexagonal chrysoberyl-type twins. The mineral is dark-green, with a pale green streak; the Mohs’ hardness is 8.5, microhardness VHN = 1725 kg/mm². D _meas = 4.25(2) g/cm³, D _calc = 4.25 g/cm³. Microscopically, it is emerald-green, pleochroic from emerald-green (γ) to yellow-green (β) and greenish yellow (α). The new mineral is biaxial (+), γ = 2.15(1), β = 2.09(3), and α = 2.05(1), 2V _meas = 80 ± (10)°, 2V _calc = 80.5°. In reflected light, it is gray with green reflections; R _max (589) = 12.9%; R _min (589) = 12.3%, and there are strong, internal green reflections. The strongest absorption bands in the IR spectrum are as follows (cm^?1): 935, 700, 614, 534. Space group Pnma, a = 9.727(3), b = 5.619(1), c = 4.499(1) Å, V = 245.9(3) ų, Z = 4. The strongest reflections in the X-ray powder diffraction pattern are as follows (d Å, I, hkl): 4.08(40)(101), 3.31(90)(111), 2.629(50)(301), 2.434(50)(220), 2.381(40)(311), 2.139(60)(221), 1.651(100)(222). The average chemical composition of mariinskite (electron microprobe, wt %) is as follows: BeO 16.3, Al₂O₃ 23.89, Cr₂O₃ 58.67, Fe₂O₃ 0.26, V₂O₃ 0.26, TiO₂ 0.61, total is 99.98. The empirical formula, calculated on the basis of four O atoms is Be_1.03(Cr_1.22Al_0.74Ti_0.01Fe_0.01V_0.01)_1.99O₄. The compatibility index 1 ? (K_p/K_c), 0.019, is excellent. The type specimens are deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, and the Ural Geological Museum, Yekaterinburg, Russia.     

Pseudosinhalite: discovery of the hydrous MgAl-borate as a new mineral in the Tayozhnoye, Siberia, skarn deposit

After its initial synthesis as the new compound Mg₂Al₃B₂O₉(OH) (Daniels et al. 1997) pseudosinhalite has now been discovered as a new mineral. It occurs, together with hydrotalcite, as a replacement product of sinhalite, MgAlBO₄, in an impure marble of the contact metasomatic iron boron deposit of Tayozhnoye in the Aldan Shield of Siberia. Its chemical composition determined by electron microprobe is (wt%): Al₂O₃ 46.88; MgO 25.12; FeO 1.99; B₂O₃ (calculated) 21.75; H₂O (calculated) 2.81 giving a total of 98.55 and leading to the empirical formula (Mg_2.00 Fe²⁺ _0.09)_Σ=2.09 Al_2.94 B₂O₉(OH). The small deviation from the ideal stoichiometry with (Mg?+?Fe²⁺):Al?≠?2:3 may be caused by either solid solution towards, or submicroscopic interlayering with lamellae of, the structurally similar mineral sinhalite. The underlying substitution involving also B and H would be (Mg?+?Fe)+?B=Al+2H. Pseudosinhalite is monoclinic, space group P2₁/c, with a=7.49(1), b=4.33(1), c=9.85(2) Å; β=110.7(1)°; V?=?299(1) ų; Z?=?2. Calculated density is 3.508?g/cm³. Pseudosinhalite is colourless with white streak and has a vitreous lustre. It is transparent; no fluorescence was detected. There is no cleavage and parting; fractures are concoidal. Optical constants could not be measured properly due to polysynthetic microtwinning, but α<1.72<γ. For synthetic pseudosinhalite α=1.691(1); β=1.713(1); γ=1.730(1); Δ=0.039; 2?V=80°. The temperature of pseudosinhalite formation was below about 400?°C at low pressures and with a hydrous, CO₂-bearing fluid participating in the reaction.     

Arcanite from Fumarole Exhalations of the Tolbachik Volcano (Kamchatka,Russia) and Its Crystal Structure

The crystal structure (R = 0.0194) of arcanite β-K₂SO₄ was studied on a single crystal from exhalations of the Arsenatnaya fumarole, Tolbachik Volcano (Kamchatka, Russia). The mineral crystallizes at a temperature of ≥350–430°C and associates with langbeinite, aphthitalite, hematite, tenorite, johillerite, and others. Arcanite is orthorhombic, Pnma, a = 7.4763(2) Å, b = 5.77262(16) Å, c = 10.0630(3) Å, V = 434.30(2) ų, Z = 4. Its structure contains isolated SO₄ tetrahedra, whereas K cations center ten- and nine-fold polyhedra.     

Crystal chemistry of Fe3+-bearing (Mg,Fe)SiO3 perovskite: a single-crystal X-ray diffraction study

Magnesium silicate perovskite is the predominant phase in the Earth’s lower mantle, and it is well known that incorporation of iron has a strong effect on its crystal structure and physical properties. To constrain the crystal chemistry of (Mg, Fe)SiO₃ perovskite more accurately, we synthesized single crystals of Mg_0.946(17)Fe_0.056(12)Si_0.997(16)O₃ perovskite at 26 GPa and 2,073 K using a multianvil press and investigated its crystal structure, oxidation state and iron-site occupancy using single-crystal X-ray diffraction and energy-domain Synchrotron Mössbauer Source spectroscopy. Single-crystal refinements indicate that all iron (Fe²⁺ and Fe³⁺) substitutes on the A-site only, where \( {\text{Fe}}^{ 3+ } /\Upsigma {\text{Fe}}\sim 20\,\% \) based on Mössbauer spectroscopy. Charge balance likely occurs through a small number of cation vacancies on either the A- or the B-site. The octahedral tilt angle (Φ) calculated for our sample from the refined atomic coordinates is 20.3°, which is 2° higher than the value calculated from the unit-cell parameters (a = 4.7877 Å, b = 4.9480 Å, c = 6.915 Å) which assumes undistorted octahedra. A compilation of all available single-crystal data (atomic coordinates) for (Mg, Fe)(Si, Al)O₃ perovskite from the literature shows a smooth increase of Φ with composition that is independent of the nature of cation substitution (e.g., \( {\text{Mg}}^{ 2+ } - {\text{Fe}}^{ 2+ } \) or \( {\text{Mg}}^{ 2+ } {\text{Si}}^{ 4+ } - {\text{Fe}}^{ 3+ } {\text{Al}}^{ 3+ } \) substitution mechanism), contrary to previous observations based on unit-cell parameter calculations.     

Mendigite,Mn2Mn2MnCa(Si3O9)2, a new mineral species of the bustamite group from the Eifel volcanic region,Germany

A new mineral, mendigite (IMA no. 2014-007), isostructural with bustamite, has been found in the In den Dellen pumice quarry near Mendig, Laacher Lake area, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany. Associated minerals are sanidine, nosean, rhodonite, tephroite, magnetite, and a pyrochlore-group mineral. Mendigite occurs as clusters of long-prismatic crystals (up to 0.1 × 0.2 × 2.5 mm in size) in cavities within sanidinite. The color is dark brown with a brown streak. Perfect cleavage is parallel to (001). D _calc = 3.56 g/cm³. The IR spectrum shows the absence of H₂O and OH groups. Mendigite is biaxial (–), α = 1.722 (calc), β = 1.782(5), γ = 1.796(5), 2V _meas = 50(10)°. The chemical composition (electron microprobe, mean of 4 point analyses, the Mn²⁺/Mn³⁺ ratio determined from structural data and charge-balance constraints) is as follows (wt %): 0.36 MgO, 10.78 CaO, 37.47 MnO, 2.91 Mn₂O₃, 4.42 Fe₂O₃, 1.08 Al₂O₃, 43.80 SiO₂, total 100.82. The empirical formula is Mn_2.00(Mn_1.33Ca_0.67) (Mn_0.50 ²⁺ Mn_0.28 ³⁺ Fe_0.15 ³⁺ Mg_0.07)(Ca_0.80 (Mn_0.20 ²⁺)(Si_5.57 Fe_0.27 ³⁺ Al_0.16O₁₈). The idealized formula is Mn₂Mn₂MnCa(Si₃O₉)₂. The crystal structure has been refined for a single crystal. Mendigite is triclinic, space group \(P\bar 1\); the unit-cell parameters are a = 7.0993(4), b = 7.6370(5), c = 7.7037(4) Å, α = 79.58(1)°, β = 62.62(1)°, γ = 76.47(1)°; V = 359.29(4) ų, Z = 1. The strongest reflections on the X-ray powder diffraction pattern [d, Å (I, %) (hkl)] are: 3.72 (32) (020), 3.40 (20) (002, 021), 3.199 (25) (012), 3.000 (26), (\(01\bar 2\), \(1\bar 20\)), 2.885 (100) (221, \(2\bar 11\), \(1\bar 21\)), 2.691 (21) (222, \(2\bar 10\)), 2.397 (21) (\(02\bar 2\), \(21\bar 1\), 203, 031), 1.774 (37) (412, \(3\bar 21\)). The type specimen is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, registration number 4420/1.     

Hydroxylborite,Mg<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)(OH)<Subscript>3</Subscript>, a new mineral species and isomorphous series fluoborite-hydroxylborite

Hydroxylborite, a new mineral species, an analogue of fluoborite with OH > F, has been found at the Titovsky deposit (57°41′N, 125°22′E), the Chersky Range, Dogdo Basin, Sakha-Yakutia Republic, Russia. Prismatic crystals of the new mineral are dominated by the {10\(\overline 1 \)0} faces without distinct end forms and reach (1?1.5) × (0.1?0.2) mm in size. Radial aggregates of such crystals occur in the mineralized marble adjacent to the boron ore (suanite-kotoite-ludwigite). Calcite, dolomite, Mg-rich ludwigite, kotoite, szaibelyite, clinohumite, magnetite, serpentine, and chlorite are associated minerals. Hydroxylborite is transparent colorless, with a white streak and vitreous luster. The new mineral is brittle. The Mohs’ hardness is 3.5. The cleavage is imperfect on {0001}. The density measured with equilibration in heavy liquids is 2.89(1) g/cm³; the calculated density is 2.872 g/cm³. The wave numbers of the absorption bands in the IR spectrum of hydroxylborite are (cm^?1; sh is shoulder): 3668, 1233, 824, 742, 630sh, 555sh, 450sh, and 407. The new mineral is optically uniaxial, negative, ω = 1.566(1), and ε = 1.531(1). The chemical composition (electron microprobe, H₂O measured with the Penfield method, wt %) is 18.43 B₂O₃, 65.71 MgO, 10.23 F, 9.73 H₂O, 4.31-O = F₂, where the total is 99.79. The empirical formula calculated on the basis of 6 anions pfu is as follows: Mg_3.03B_0.98[(OH)_2.00F_1.00]O_3.00. Hydroxylborite is hexagonal, and the space group is P6₃/m. The unit-cell dimensions are: a = 8.912(8) Å, c = 3.112(4) Å, V = 214.05(26) ų, and Z = 2. The strongest reflections in the X-ray powder pattern [d, Å (I, %)(hkil)] are: 7.69(52)(01\(\overline 1 \)0), 4.45(82)(11\(\overline 2 \)0), 2.573(65)(03\(\overline 3 \)0), 2.422(100)(02\(\overline 2 \)1), and 2.128(60)(12\(\overline 3 \)1). The compatibility index 1 ? (K _p/K _c) is 0.038 (excellent) for the calculated density and 0.044 (good) for the measured density. The type material of hydroxylborite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow (inventory number 91968) and the Geological Museum of the All-Russia Institute of Mineral Resources, Moscow (inventory number M-1663).     

Oxyvanite,V<Subscript>3</Subscript>O<Subscript>5</Subscript>, a new mineral species and the oxyvanite-berdesinskiite V<Subscript>2</Subscript>TiO<Subscript>5</Subscript> series from metamorphic rocks of the Slyudyanka Complex,southern Baikal region

Oxyvanite has been identified as an accessory mineral in Cr-V-bearing quartz-diopside meta- morphic rocks of the Slyudyanka Complex in the southern Baikal region, Russia. The new mineral was named after constituents of its ideal formula (oxygen and vanadium). Quartz, Cr-V-bearing tremolite and micas, calcite, clinopyroxenes of the diopside-kosmochlor-natalyite series, Cr-bearing goldmanite, eskolaite-karelianite dravite-vanadiumdravite, V-bearing titanite, ilmenite, and rutile, berdesinskiite, schreyerite, plagioclase, scapolite, barite, zircon, and unnamed U-Ti-V-Cr phases are associated minerals. Oxyvanite occurs as anhedral grains up to 0.1–0.15 mm in size, without visible cleavage and parting. The new mineral is brittle, with conchoidal fracture. Observed by the naked eye, the mineral is black, with black streak and resinous luster. The microhardness (VHN) is 1064–1266 kg/mm² (load 30 g), and the mean value is 1180 kg/mm². The Mohs hardness is about 7.0–7.5. The calculated density is 4.66(2) g/cm³. The color of oxyvanite is pale cream in reflected light, without internal reflections. The measured reflectance in air is as follows (λ, nm-R, %): 440-17.8; 460-18; 480-18.2; 520-18.6; 520-18.6; 540-18.8; 560-18.9; 580-19; 600-19.1; 620-19.2; 640-19.3; 660-19.4; 680-19.5; 700-19.7. Oxyvanite is monoclinic, space group C2/c; the unit-cell dimensions are a = 10.03(2), b = 5.050(1), c = 7.000(1) Å, β = 111.14(1)°, V = 330.76(5)ų, Z = 4. The strongest reflections in the X-ray powder pattern [d, Å, (I in 5-number scale)(hkl)] are 3.28 (5) (20\(\bar 2\)); 2.88 (5) (11\(\bar 2\)); 2.65, (5) (310); 2.44 (5) (112); 1.717 (5) (42\(\bar 2\)); 1.633 (5) (31\(\bar 4\)); 1.446 (4) (33\(\bar 2\)); 1.379 (5) (422). The chemical composition (electron microprobe, average of six point analyses, wt %): 14.04 TiO₂, 73.13 V₂O₃ (53.97 V₂O_3calc, 21.25 VO_2calc), 10.76 Cr₂O₃, 0.04 Fe₂O₃, 0.01 Al₂O₃, 0.02 MgO, total is 100.03. The empirical formula is (V _1.70 ³⁺ Cr_0.30)_2.0(V _0.59 ⁴⁺ Ti_0.41)_1.0O₅. Oxyvanite is the end member of the oxyvanite-berdesinskiite series with homovalent isomorphic substitution of V⁴⁺ for Ti. The type material has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.     

Ertixiite—a new mineral from the Altay Pegmatite Mine,Xinjiang, China

Ertixiite (Na₂Si₄O₉), a new mineral found in a miarolitic cavity of the Altay Pegmatite Mine, Xinjiang, China, is associated with topaz, apatite, quartz, cleavelandite, etc. The mineral is white, granular, and transparent. HNV=570.08?850.96 kg/mm² (Moh’s 5.8?6.5), D=2.35, N=1.502. Cubic system,a=5.975 Å, V=213.311 Å, Z=1,D _x =2.34g/cm³. The chemical composition of ertixiite (the average of six samples) is: Na₂O 17.97, CaO 2.82, SiO₂ 77.86, Al₂O₃ 1.45, FeO 0.05, total 100.15. The strongest lines in the X-ray powder pattern are 3.443(2, 111), 2.647(2. 210), 2.674(2,210), 1.996(8,221), 1.798(10,311), and 1.492(2,400).     

Quintinite-1<Emphasis Type="Italic">M</Emphasis> from the Mariinsky Deposit,Ural Emerald Mines,Central Urals,Russia

The paper describes the first finding of quintinite [Mg₄Al₂(OH)₁₂][(CO₃)(H₂O)₃] at the Mariinsky deposit in the Central Urals, Russia. The mineral occurs as white tabular crystals in cavities within altered gabbro in association with prehnite, calcite, and a chlorite-group mineral. Quintinite is the probable result of late hydrothermal alteration of primary mafic and ultramafic rocks hosting emerald-bearing glimmerite. According to electron microprobe data, the Mg: Al ratio is ~2: 1. IR spectroscopy has revealed hydroxyl and carbonate groups and H₂O molecules in the mineral. According to single crystal XRD data, quintinite is monoclinic, space group C2/m, a =5.233(1), b = 9.051(2), c = 7.711(2) Å, β = 103.09(3)°, V = 355.7(2) ų. Based on structure refinement, the polytype of quintinite should be denoted as 1M. This is the third approved occurrence of quintinite-1M in the world after the Kovdor complex and Bazhenovsky chrysotile–asbestos deposit.     

A New Three–Dimensional Superstructure in Bafertisite

A new superstructure was found in bafertisite [(Ba0.98Na0.02)1.00(Fe1.71Mn0.26Mg0.01)1.98 TiO[(Si1.82Ti0.04Al0.03Cr0.01)1.90O7](OH1.40F0.53Cl0.03)1.96] from Donghai County, Jiangsu Province, China. The occurrence of the superstructure reflections were observed by single crystal diffraction using a SMAR APEX CCD. The a*, b*and c* axis directions revealed extra weak reflection spots of the superstructure. The apparent 2a, 2b and 2c superstructure is monoclinic with unit cell a＝10.6502(15)?, b＝13.7233(19)?, c＝21.6897(3)?, α＝90o, β＝94.698(3)o, γ＝90o,space group Cm,Z=16. If c* extra weak reflections are ignored, the secondary supercell gave a cell a＝10.6548(15)?, b＝13.7284(19)?, c＝11.6900(17)?, α＝90o, β＝112.322(28)o, γ＝90o,space group Cm,Z=8. The basic subcell was obtained by ignoring all extra weak reflection spots and gave: a＝5.3249(17)?, b＝6.8669(22)?, c＝10.8709(36)?, α＝90o, β＝94.740(62)o, γ＝90o,space P21/m,Z=2. The superstructure has been refined to R = 0.063 for 7805 [R(int) = 0.0266] unique reflections I>2δ(I). The structure consists of an octahedra (O) sheet sandwiched between two heteropolyhedral (H) sheets. These sheets consist of Ti–octahedra and twin tetrahedral disilicate groups [Si2O7]. The O sheet comprises (Fe,Mg)O4 octahedra. The large Ba cation is located in the interlayer area. The refined structure shows Fe, Mg are partly ordered. The shifting of the TiO6 octahedron and SiO4 tetrahedron sites in the sheet may be a consequence of the superstructure.     

Karchevskyite, [Mg18Al9(OH)54][Sr2(CO3,PO4)9(H2O,H3O)11], a new mineral species of the layered double hydroxide family

Karchevskyite, a new mineral related to the family of layered double hydroxides (LDHs), has been found in the Iron open pit at the Kovdor carbonatite massif, Kola Peninsula, Russia. The mineral occurs as spherulites of up to 1.5 mm in diameter composed of thin, curved lamellae. Dolomite, magnetite, quintinite-3T, strontium carbonate, and fluorapatite are associated minerals. Karchevskyite is white in aggregates and colorless in separate platelets. Its luster is vitreous with a pearly shine on the cleavage surface. The new mineral is nonfluorescent. The Mohs hardness is 2. The cleavage is eminent (micalike), parallel to {001}. The measured density is 2.21(2) g/cm³, and the calculated value is 2.18(1) g/cm³. Karchevskyite is colorless and nonpleochroic in immersion liquids. It is uniaxial, negative, ω = 1.542(2), and ? = 1.534(2). The chemical composition (electron microprobe, average of ten point analyses, standard deviation in parentheses, wt %) is as follows: 29.7(1.1) MgO, 18.3(0.7) Al₂O₃, 7.4(0.4) SrO, 0.2(0.1) CaO, 1.3(0.2) P₂O₅, 14.5(0.4) CO₂, and 28.6 H₂O (estimated by difference); the total is 100. The empirical formula calculated on the basis of nine Al atoms is Mg_18.00Al_9.00(OH)_54.00(Sr_1.79Mg_0.48Ca_0.09)_2.36 (Ca₃)_8.26(PO₄)_0.46(H₂O)_6.54(H₃O)_4.18. The idealized formula is [Mg₁₈Al₉(OH)₅₄][Sr₂(CO₃, PO₄)₉(H₂O, H₃O)₁₁]. The new mineral slowly dissolves in 10% HCl with weak effervescence. Karchevskyite is trigonal; possible space groups are P3, P3, P $ \overline 3 Karchevskyite, a new mineral related to the family of layered double hydroxides (LDHs), has been found in the Iron open pit at the Kovdor carbonatite massif, Kola Peninsula, Russia. The mineral occurs as spherulites of up to 1.5 mm in diameter composed of thin, curved lamellae. Dolomite, magnetite, quintinite-3T, strontium carbonate, and fluorapatite are associated minerals. Karchevskyite is white in aggregates and colorless in separate platelets. Its luster is vitreous with a pearly shine on the cleavage surface. The new mineral is nonfluorescent. The Mohs hardness is 2. The cleavage is eminent (micalike), parallel to {001}. The measured density is 2.21(2) g/cm³, and the calculated value is 2.18(1) g/cm³. Karchevskyite is colorless and nonpleochroic in immersion liquids. It is uniaxial, negative, ω = 1.542(2), and ɛ = 1.534(2). The chemical composition (electron microprobe, average of ten point analyses, standard deviation in parentheses, wt %) is as follows: 29.7(1.1) MgO, 18.3(0.7) Al₂O₃, 7.4(0.4) SrO, 0.2(0.1) CaO, 1.3(0.2) P₂O₅, 14.5(0.4) CO₂, and 28.6 H₂O (estimated by difference); the total is 100. The empirical formula calculated on the basis of nine Al atoms is Mg_18.00Al_9.00(OH)_54.00(Sr_1.79Mg_0.48Ca_0.09)_2.36 (Ca₃)_8.26(PO₄)_0.46(H₂O)_6.54(H₃O)_4.18. The idealized formula is [Mg₁₈Al₉(OH)₅₄][Sr₂(CO₃, PO₄)₉(H₂O, H₃O)₁₁]. The new mineral slowly dissolves in 10% HCl with weak effervescence. Karchevskyite is trigonal; possible space groups are P3, P3, P 1m, P31m, P312, P312, P3m1, or P3m1; unit-cell dimensions are a = 16.055(6), c = 25.66(1) ?, V = 5728(7) ?³, Z = 3. The strongest reflections in the X-ray powder diffraction pattern [d, (I, %)(hkl)] are: 8.52(10)(003), 6.41(4)(004), 5.13(3)(005), 4.27(6)(006), 3.665(9)(007), 3.547(9)(107), 3.081(6)(315). Wavenumbers of absorption bands in the infrared spectrum of the new mineral are (cm⁻¹; s is shoulder): 3470, 3420s, 3035, 2960s, 1650, 1426, 1366, 1024, 937, 860, 779, 678, 615s, 553, 449, 386. Results of thermogravimetric analysis: total weight loss is 42.0 wt %, with three stages of loss: 12.2%, maximum rate at 230°C; 6.1%, maximum rate at 320°C; and 23.7%, maximum rate at 440°C. Karchevskyite is a late-stage hydrothermal mineral. The mineral is named in memory of Russian mineralogist Pavel Karchevsky (1976–2002), who made a significant contribution to the study of carbonatites. The type material of karchevskyite is deposited at the Mineralogical Museum, Division of Mineralogy, St. Petersburg State University, and the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. Original Russian Text ? S.N. Britvin, N.V. Chukanov, G.K. Bekenova, M.A. Yagovkina, A.V. Antonov, A.N. Bogdanova, N.I. Krasnova, 2007, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2007, No. 5, pp. 44–56. The new mineral karchevskyite and its name accepted by the Commission on New Minerals and Mineral Names, Russian Mineralogical Society, March 21, 2005. Approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, June 30, 2005.     

Cation substitution in synthetic meridianiite (MgSO<Subscript>4</Subscript>·11H<Subscript>2</Subscript>O) I: X-ray powder diffraction analysis of quenched polycrystalline aggregates

Meridianiite, MgSO₄·11H₂O, is the most highly hydrated phase in the binary MgSO₄–H₂O system. Lower hydrates in the MgSO₄–H₂O system have end-member analogues containing alternative divalent metal cations (Ni²⁺, Zn²⁺, Mn²⁺, Cu²⁺, Fe²⁺, and Co²⁺) and exhibit extensive solid solution with MgSO₄ and with one another, but no other undecahydrate is known. We have prepared aqueous MgSO₄ solutions doped with these other cations in proportions up to and including the pure end-members. These liquids have been solidified into fine-grained polycrystalline blocks of metal sulfate hydrate + ice by rapid quenching in liquid nitrogen. The solid products have been characterised by X-ray powder diffraction, and the onset of partial melting has been quantified using a thermal probe. We have established that of the seven end-member metal sulfates studied, only MgSO₄ forms an undecahydrate; ZnSO₄ forms an orthorhombic heptahydrate (synthetic goslarite), MnSO₄, FeSO₄, and CoSO₄ form monoclinic heptahydrates (syn. mallardite, melanterite, bieberite, respectively), and CuSO₄ crystallises as the well-known triclinic pentahydrate (syn. chalcanthite). NiSO₄ forms a new hydrate which has been indexed with a triclinic unit cell of dimensions a = 6.1275(1) Å, b = 6.8628(1) Å, c = 12.6318(2) Å, α = 92.904(2)°, β = 97.678(2)°, and γ = 96.618(2)°. The unit-cell volume of this crystal, V = 521.74(1) ų, is consistent with it being an octahydrate, NiSO₄·8H₂O. Further analysis of doped specimens has shown that synthetic meridianiite is able to accommodate significant quantities of foreign cations in its structure; of the order 50 mol. % Co²⁺ or Mn²⁺, 20–30 mol. % Ni²⁺ or Zn²⁺, but less than 10 mol. % of Cu²⁺ or Fe²⁺. In three of the systems we examined, an ‘intermediate’ phase occurred that differed in hydration state both from the Mg-bearing meridianiite end-member and the pure dopant end-member hydrate. In the case of CuSO₄, we observed a melanterite-structured heptahydrate at Cu/(Cu + Mg) = 0.5, which we identify as synthetic alpersite [(Mg_0.5Cu_0.5)SO₄·7H₂O)]. In the NiSO₄- and ZnSO₄-doped systems we characterised an entirely new hydrate which could also be identified to a lesser degree in the CuSO₄- and the FeSO₄-doped systems. The Ni-doped substance has been indexed with a monoclinic unit-cell of dimensions a = 6.7488(2) Å, b = 11.9613(4) Å, c = 14.6321(5) Å, and β = 95.047(3)°, systematic absences being indicative of space-group P2₁/c with Z = 4. The unit-cell volume, V = 1,176.59(5) ų, is consistent with it being an enneahydrate [i.e. (Mg_0.5Ni_0.5)SO₄·9H₂O)]. Similarly, the new Zn-bearing enneahydrate has refined unit cell dimensions of a = 6.7555(3) Å, b = 11.9834(5) Å, c = 14.6666(8) Å, β = 95.020(4)°, V = 1,182.77(7) ų, and the new Fe-bearing enneahydrate has refined unit cell dimensions of a = 6.7726(3) Å, b = 12.0077(3) Å, c = 14.6920(5) Å, β = 95.037(3)°, and V = 1,190.20(6) ų. The observation that synthetic meridianiite can form in the presence of, and accommodate significant quantities of other ions increases the likelihood that this mineral will occur naturally on Mars—and elsewhere in the outer solar system—in metalliferous brines.     

Vladimirivanovite, Na6Ca2[Al6Si6O24](SO4,S3,S2,Cl)2 · H2O, a new mineral of sodalite group

The results of an examination of vladimirivanovite, a new mineral of the sodalite group, found at the Tultui deposit in the Baikal region are discussed. The mineral occurs in the form of outer rims (0.01–3 mm thick) of lazurite, elongated segregations without faced crystals (0.2 to 3–4 mm in size; less frequently, 4 × 12–15 × 20 mm), and rare veinlets (up to 5 mm) hosted in calciphyre and marble. Vladimirivanovite is irregular and patchy dark blue. The mineral is brittle; on average, the microhardness VHN is 522–604, 575 kg/mm²; and the Mohs hardness is 5.0–5.5. The measured and calculated densities are 2.48(3) and 2.436 g/cm³, respectively. Vladimirivanovite is optically biaxial; 2V _meas = 63(±1)°, 2V _calc = 66.2°; the refractive indices are α = 1.502–1.507 (±0.002), N _m = 1.509–1.514 (±0.002), and N _g = 1.512–1.517 (±0.002). The chemical composition is as follows, wt %: 32.59 SiO₂, 27.39 Al₂O₃, 7.66 CaO, 17.74 Na₂O, 11.37 SO₃, 1.94 S, 0.12 Cl, and 1.0 H₂O; total is 99.62. The empirical formula calculated based on (Si + Al) = 12 with sulfide sulfur determined from the charge balance is Na_6.36Ca_1.52(Si_6.03Al_5.97)_Σ12O_23.99(SO₄)_1.58(S₃)_0.17(S₂)_0.08 · Cl_0.04 · 0.62H₂O; the idealized formula is Na₆Ca₂[Al₆Si₆O₂₄](SO₄,S₃,S₂,Cl)₂ · H₂O. The new mineral is orthorhombic, space group Pnaa; the unit-cell dimensions are a = 9.066, b = 12.851, c = 38.558 Å, V = 4492 ų, and Z = 6. The strongest reflections in the X-ray powder diffraction pattern (dÅ—I[hkl]) are: 6.61–5[015], 6.43–11[020, 006], 3.71–100[119, 133], 2.623–30[20.12, 240], 2.273–6[04.12], 2.141–14[159, 13.15], 1.783–9[06.12, 04.18], and 1.606–6[080, 00.24]. The crystal structure has been solved with a single crystal. The mineral was named in memoriam of Vladimir Georgievich Ivanov (1947–2002), Russian mineralogist and geochemist. The type material of the mineral is deposited at the Mineralogical Museum of St. Petersburg State University, St. Petersburg, Russia.