Nickeltalmessite,Ca<Subscript>2</Subscript>Ni(AsO<Subscript>4</Subscript>)<Subscript>2</Subscript> · 2H<Subscript>2</Subscript>O,a new mineral species of the fairfieldite group,Bou Azzer,Morocco

Nickeltalmessite, Ca₂Ni(AsO₄)₂ · 2H₂O, a new mineral species of the fairfieldite group, has been found in association with annabergite, nickelaustinite, pecoraite, calcite, and a mineral of the chromite-manganochromite series from the dump of the Aït Ahmane Mine, Bou Azzer ore district, Morocco. The new mineral occurs as spheroidal aggregates consisting of split crystals up to 10 × 10 × 20 μm in size. Nickeltalmessite is apple green, with white streak and vitreous luster. The density measured by the volumetric method is 3.72(3) g/cm³; calculated density is 3.74 g/cm³. The new mineral is colorless under a microscope, biaxial, positive: α = 1.715(3), β = 1.720(5), γ = 1.753(3), 2V _meas = 80(10)°, 2V _calc = 60.4. Dispersion is not observed. The infrared spectrum is given. As a result of heating of the mineral in vacuum from 24° up to 500°C, weight loss was 8.03 wt %. The chemical composition (electron microprobe, wt %) is as follows: 25.92 CaO, 1.23 MgO, 1.08 CoO, 13.01 NiO, 52.09 As₂O₅; 7.8 H₂O (determined by the Penfield method); the total is 101.13. The empirical formula calculated on the basis of two AsO₄ groups is Ca_2.04(Ni_0.77Mg_0.13Co_0.06)_Σ0.96 (AsO₄)_2.00 · 1.91H₂O. The strongest reflections in the X-ray powder diffraction pattern [d, Å (I, %) (hkl)] are: 5.05 (27) (001) (100), 3.57 (43) (011), 3.358 (58) (110), 3.202 (100) (020), 3.099 (64) (0\(\bar 2\)1), 2.813 (60), (\(\bar 1\)21), 2.772 (68) (2\(\bar 1\)0), 1.714 (39) (\(\bar 3\)31). The unit-cell dimensions of the triclinic lattice (space group P1 or P) determined from the X-ray powder data are: a = 5.858(7), b = 7.082(12), c = 5.567(6) Å, α = 97.20(4), β = 109.11(5), γ = 109.78(5)°, V = 198.04 ų, Z = 1. The mineral name emphasizes its chemical composition as a Ni-dominant analogue of talmessite. The type material of nickeltalmessite is deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, registration number 3750/1.     

Parageorgbokiite, β-Cu<Subscript>5</Subscript>O<Subscript>2</Subscript>(SeO<Subscript>3</Subscript>)<Subscript>2</Subscript>Cl<Subscript>2</Subscript>, a new mineral species from volcanic exhalations,Kamchatka Peninsula,Russia

Parageorgbokiite, β-Cu₅O₂(SeO₃)₂Cl₂, has been found at the second cinder cone of the Great Fissure Tolbachik Eruption, Kamchatka Peninsula, Russia. Ralstonite, tolbachite, melanothallite, chalcocyanite, euchlorine, Fe oxides, tenorite, native gold, sophiite, Na, Ca, and Mg sulfates, cotunnite, and some copper oxoselenites are associated minerals. The estimated temperature of the mineral formation is 400–625°C. The color is green, with a vitreous luster; the streak is light green. The mineral is brittle, with the Mohs hardness ranging from 3 to 4. Cleavage is not observed. The calculated density is 4.70 g/cm³. Parageorgbokiite is biaxial (+); α = 2.05(1), β = 2.05(1), and γ = 2.08(1); 2V _(meas.) is ～0³, and 2V _(calc.) = 0(5)°. The optical orientation is X = a; other details remain unclear. The mineral is pleochroic, from grass green on X and Y to yellowish green on Z. The empirical formula calculated on the basis of O + Cl = 10 is Cu_4.91Pb_0.02O_1.86(ScO₃)₂Cl_2.14. The simplified formula is Cu₅O₂(ScO₃)₂Cl₂. Parageorgbokiite pertains to a new structural type of inorganic compounds. Its name points out its dimorphism with georgbokiite, which was named in honor of G.B. Bokii, the prominent Russian crystal chemist (1909–2000).     

Middendorfite,K<Subscript>3</Subscript>Na<Subscript>2</Subscript>Mn<Subscript>5</Subscript>Si<Subscript>12</Subscript>(O,OH)<Subscript>36</Subscript> · 2H<Subscript>2</Subscript>O,a new mineral species from the Khibiny pluton,Kola Peninsula

Middendorfite, a new mineral species, has been found in a hydrothermal assemblage in Hilairite hyperperalkaline pegmatite at the Kirovsky Mine, Mount Kukisvumchorr apatite deposit, Khibiny alkaline pluton, Kola Peninsula, Russia. Microcline, sodalite, cancrisilite, aegirine, calcite, natrolite, fluorite, narsarsukite, labuntsovite-Mn, mangan-neptunite, and donnayite are associated minerals. Middendorfite occurs as rhombshaped lamellar and tabular crystals up to 0.1 × 0.2 × 0.4 mm in size, which are combined in worm-and fanlike segregations up to 1 mm in size. The color is dark to bright orange, with a yellowish streak and vitreous luster. The mineral is transparent. The cleavage (001) is perfect, micalike; the fracture is scaly; flakes are flexible but not elastic. The Mohs hardness is 3 to 3.5. Density is 2.60 g/cm³ (meas.) and 2.65 g/cm³ (calc.). Middendorfite is biaxial (?), α = 1.534, β = 1.562, and γ = 1.563; 2V (meas.) = 10°. The mineral is pleochroic strongly from yellowish to colorless on X through brown on Y and to deep brown on Z. Optical orientation: X = c. The chemical composition (electron microprobe, H₂O determined with Penfield method) is as follows (wt %): 4.55 Na₂O, 10.16 K₂O, 0.11 CaO, 0.18 MgO, 24.88 MnO, 0.68 FeO, 0.15 ZnO, 0.20 Al₂O₃, 50.87 SiO₂, 0.17 TiO₂, 0.23 F, 7.73 H₂O; ?O=F₂?0.10, total is 99.81. The empirical formula calculated on the basis of (Si,Al)₁₂(O,OH,F)₃₆ is K_3.04(Na_2.07Ca_0.03)_Σ2.10(Mn_4.95Fe_0.13Mg_0.06Ti_0.03Zn_0.03)_Σ5.20(Si_11.94Al_0.06)_Σ12O_27.57(OH)_8.26F_0.17 · 1.92H₂O. The simplified formula is K₃Na₂Mn₅Si₁₂(O,OH)₃₆ · 2H₂O. Middenforite is monoclinic, space group: P2₁/m or P2₁. The unit cell dimensions are a = 12.55, b = 5.721, c = 26.86 Å; β = 114.04°, V = 1761 ų, Z = 2. The strongest lines in the X-ray powder pattern [d, Å, (I)(hkl)] are: 12.28(100)(002), 4.31(81)(11\(\overline 4 \)), 3.555(62)(301, 212), 3.063(52)(008, 31\(\overline 6 \)), 2.840(90)(312, 021, 30\(\overline 9 \)), 2.634(88)(21\(\overline 9 \), 1.0.\(\overline 1 \)0, 12\(\overline 4 \)), 2.366(76)(22\(\overline 6 \), 3.1.\(\overline 1 \)0, 32\(\overline 3 \)), 2.109(54)(42–33, 42–44, 51\(\overline 9 \), 414), 1.669(64)(2.2.\(\overline 1 \)3, 3.2.\(\overline 1 \)3, 62\(\overline 3 \), 6.1.\(\overline 1 \)3), 1.614(56)(5.0.\(\overline 1 \)6, 137, 333, 71\(\overline 1 \)). The infrared spectrum is given. Middendorfite is a phyllosilicate related to bannisterite, parsenttensite, and the minerals of the ganophyllite and stilpnomelane groups. The new mineral is named in memory of A.F. von Middendorff (1815–1894), an outstanding scientist, who carried out the first mineralogical investigations in the Khibiny pluton. The type material of middenforite has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.     

Spectroscopic studies of synthetic and natural ringwoodite, γ-(Mg,Fe)<Subscript>2</Subscript>SiO<Subscript>4</Subscript>

Synthetic ringwoodite γ-(Mg_1?x Fe _x )₂SiO₄ of 0.4 ≤ x ≤ 1.0 compositions and variously colored micro-grains of natural ringwoodite in shock metamorphism veins of thin sections of two S6-type chondrites were studied by means of microprobe analysis, TEM and optical absorption spectroscopy. Three synthetic samples were studied in addition with Mössbauer spectroscopy. The Mössbauer spectra consist of two doublets caused by ^VIFe²⁺ and ^VIFe³⁺, with IS and QS parameters close to those established elsewhere (e.g., O’Neill et al. in Am Mineral 78:456–460, 1993). The Fe³⁺/Fe_total ratio evaluated by curve resolution of the spectra, ranges from 0.04 to 0.1. Optical absorption spectra of all synthetic samples studied are qualitatively very similar as they are directly related to the iron content. They differ mostly in the intensity of the observed absorption features. The spectra consist of a very strong high-energy absorption edge and a series of absorption bands of different width and intensity. The three strongest and broadest absorptions of them are attributed to splitting of electronic spin-allowed ⁵ T _2g → ⁵ E _g transitions of ^VIFe²⁺ and intervalence charge-transfer (IVCT) transition between ferrous and ferric ions in adjacent octahedral sites of the ringwoodite structure. The spin-allowed bands at ca. 8,000 and 11,500 cm^?1 weakly depend on temperature, whilst the Fe²⁺/Fe³⁺ IVCT band at ~16,400 cm^?1 displays very strong temperature dependence: i.e., with increasing temperature it decreases and practically disappears at about 497 K, a behavior typical for bands of this type. With increasing pressure the absorption edge shifts to lower energies while the spin-allowed bands shift to higher energy and strongly decreases in intensity. The IVCT band also strongly weakens and vanishes at about 9 GPa. We assigned this effect to pressure-induced reduction of Fe³⁺ in ringwoodite. By analogy with synthetic samples three broad bands in spectra of natural (meteoritic) blue ringwoodite are assigned to electronic spin-allowed transitions of ^VIFe²⁺ (the bands at ~8,600 and ~12,700 cm^?1) and Fe²⁺/Fe³⁺ IVCT transition (~18,100 cm^?1), respectively. Spectra of colorless ringwoodite of the same composition consist of a single broad band at ca. 12,000 cm^?1. It is assumed that such ringwoodite grains are inverse (Fe, Mg)₂SiO₄-spinels and that the single band is caused by the split spin-allowed ⁵ E → ⁵ T ₂ transition of ^IVFe²⁺. Ringwoodite of intermediate color variations between dark-blue and colorless are assumed to be partly inversed ringwoodite. No glassy material between the grain boundaries in the natural colored ringwoodite aggregates was found in our samples and disprove the cause of the coloration to be due to light scattering effect (Lingemann and Stöffler in Lunar Planet Sci 29(1308), 1998).     

Dachiardite-K, (K<Subscript>2</Subscript>Ca)(Al<Subscript>4</Subscript>Si<Subscript>20</Subscript>O<Subscript>48</Subscript>) · 13H<Subscript>2</Subscript>O,a new zeolite from Eastern Rhodopes,Bulgaria

Dachiardite-K (IMA No. 2015-041), a new zeolite, is a K-dominant member of the dachiardite series with the idealized formula (К₂Са)(Al₄Si₂₀O₄₈) · 13H₂О. It occurs in the walls of opal–chalcedony veinlets cutting hydrothermally altered effusive rocks of the Zvezdel paleovolcanic complex near the village of Austa, Momchilgrad Municipality, Eastern Rhodopes, Bulgaria. Chalcedony, opal, dachiardite-Ca, dachiardite-Na, ferrierite-Mg, ferrierite-K, clinoptilolite-Ca, clinoptilolite-K, mordenite, smectite, celadonite, calcite, and barite are associated minerals. The mineral forms radiated aggregates up to 8 mm in diameter consisting of split acicular individuals. Dachiardite-K is white to colorless. Perfect cleavage is observed on (100). D _meas = 2.18(2), D _calc = 2.169 g/cm³. The IR spectrum is given. Dachiardite-K is biaxial (+), α = 1.477 (calc), β = 1.478(2), γ = 1.481(2), 2V _meas = 65(10)°. The chemical composition (electron microprobe, mean of six point analyses, H₂O determined by gravimetric method) is as follows, wt %: 4.51 K₂O, 3.27 CaO, 0.41 BaO, 10.36 A1₂O₃, 67.90 SiO₂, 13.2 H₂O, total is 99.65. The empirical formula is H_26.23K_1.71Ca_1.04Ba_0.05Al_3.64Si_20.24O₆₁. The strongest reflections in the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 9.76 (24) (001), 8.85 (58) (200), 4.870 (59) (002), 3.807 (16) (202), 3.768 (20) (112, 020), 3.457 (100) (220), 2.966 (17) (602). Dachiardite-K is monoclinic, space gr. C2/m, Cm or C2; the unit cell parameters refined from the powder X-ray diffraction data are: a = 18.670(8), b = 7.511(3), c = 10.231(4) Å, β = 107.79(3)°, V= 1366(1) ų, Z = 1. The type specimen has been deposited in the Earth and Man National Museum, Sofia, Bulgaria, with the registration number 23927.     

Attikaite,Ca<Subscript>3</Subscript>Cu<Subscript>2</Subscript>Al<Subscript>2</Subscript>(AsO<Subscript>4</Subscript>)<Subscript>4</Subscript>(OH)<Subscript>4</Subscript> · 2H<Subscript>2</Subscript>O,a new mineral species

Attikaite, a new mineral species, has been found together with arsenocrandalite, arsenogoyazite, conichalcite, olivenite, philipsbornite, azurite, malachite, carminite, beudantite, goethite, quartz, and allophane at the Christina Mine No. 132, Kamareza, Lavrion District, Attiki Prefecture (Attika), Greece. The mineral is named after the type locality. It forms spheroidal segregations (up to 0.3 mm in diameter) consisting of thin flexible crystals up to 3 × 20 × 80 μm in size. Its color is light blue to greenish blue, with a pale blue streak. The Mohs’ hardness is 2 to 2.5. The cleavage is eminent mica-like parallel to {001}. The density is 3.2(2) g/cm³ (measured in heavy liquids) and 3.356 g/cm³ (calculated). The wave numbers of the absorption bands in the infrared spectrum of attikaite are (cm^?1; sh is shoulder; w is a weak band): 3525sh, 3425, 3180, 1642, 1120w, 1070w, 1035w, 900sh, 874, 833, 820, 690w, 645w, 600sh, 555, 486, 458, and 397. Attikaite is optically biaxial, negative, α = 1.642(2), β = γ = 1.644(2) (X = c) 2V _means = 10(8)°, and 2V _calc = 0°. The new mineral is microscopically colorless and nonpleochroic. The chemical composition (electron microprobe, average over 4 point analyses, wt %) is: 0.17 MgO, 17.48 CaO, 0.12 FeO, 16.28 CuO, 10.61 Al₂O₃, 0.89 P₂O₅, 45.45 As₂O₅, 1.39 SO₃, and H₂O (by difference) 7.61, where the total is 100.00. The empirical formula calculated on the basis of (O,OH,H₂O)₂₂ is: Ca_2.94Cu _1.93 ²⁺ Al_1.97Mg_0.04Fe _0.02 ²⁺ [(As_3.74S_0.16P_0.12)_Σ4.02O_16.08](OH)_3.87 · 2.05H₂ O. The simplified formula is Ca₃Cu₂Al₂(AsO₄)₄(OH)₄ · 2H₂O. Attikaite is orthorhombic, space group Pban, Pbam or Pba2; the unit-cell dimensions are a = 10.01(1), b = 8.199(5), c = 22.78(1) Å, V = 1870(3) ų, and Z = 4. In the result of the ignition of attikaite for 30 to 35 min at 128–140°, the H₂O bands in the IR spectrum disappear, while the OH-group band is not modified; the weight loss is 4.3%, which approximately corresponds to two H₂O molecules per formula; and parameter c decreases from 22.78 to 18.77 Å. The strongest reflections in the X-ray powder diffraction pattern [d, Å (I, %)((hkl)] are: 22.8(100)(001), 11.36(60)(002), 5.01(90)(200), 3.38(5)(123, 205), 2.780(70)(026), 2.682(30)(126), 2.503(50)(400), 2.292(20)(404). The type material of attikaite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. The registration number is 3435/1.     

Room-temperature equation of state of Li<Subscript>2</Subscript>VOSiO<Subscript>4</Subscript> up to 8.5 GPa

High-pressure single-crystal X-ray diffraction measurements of lattice parameters of the compound Li₂VOSiO₄, which crystallises with a natisite-type structure, has been carried out to a pressure of 8.54(5) GPa at room temperature. Unit-cell volume data were fitted with a second-order Birch-Murnaghan EoS (BM-EoS), simultaneously refining V ₀ and K ₀ using the data weighted by the uncertainties in V. The bulk modulus is K ₀ = 99(1) GPa, with K′ fixed to 4. Refinements of third order equations-of-state yielded values of K′ that did not differ significantly from 4. The compressibility of the unit-cell is strongly anisotropic with the c axis (K ₀(c) = 49.7 ± 0.5 GPa) approximately four times more compressible than the a axis (K ₀(a) = 195 ± 3 GPa).     

Nickelpicromerite,K<Subscript>2</Subscript>Ni(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>•6H<Subscript>2</Subscript>O,a new picromerite-group mineral from Slyudorudnik,South Urals,Russia

A new picromerite-group mineral, nickelpicromerite, K₂Ni(SO₄)₂?·?6H₂O (IMA 2012–053), was found at the Vein #169 of the Ufaley quartz deposit, near the town of Slyudorudnik, Kyshtym District, Chelyabinsk area, South Urals, Russia. It is a supergene mineral that occurs, with gypsum and goethite, in the fractures of slightly weathered actinolite-talc schist containing partially vermiculitized biotite and partially altered sulfides: pyrrhotite, pentlandite, millerite, pyrite and marcasite. Nickelpicromerite forms equant to short prismatic or tabular crystals up to 0.07 mm in size and anhedral grains up to 0.5 mm across, their clusters or crusts up to 1 mm. Nickelpicromerite is light greenish blue. Lustre is vitreous. Mohs hardness is 2–2½. Cleavage is distinct, parallel to {10–2}. D _meas is 2.20(2), D _calc is 2.22 g cm^?3. Nickelpicromerite is optically biaxial (+), α?=?1.486(2), β?=?1.489(2), γ?=?1.494(2), 2V_meas =75(10)°, 2V_calc =76°. The chemical composition (wt.%, electron-microprobe data) is: K₂O 20.93, MgO 0.38, FeO 0.07, NiO 16.76, SO₃ 37.20, H₂O (calc.) 24.66, total 100.00. The empirical formula, calculated based on 14 O, is: K_1.93Mg_0.04Ni_0.98S_2.02O_8.05(H₂O)_5.95. Nickelpicromerite is monoclinic, P2₁/c, a?=?6.1310(7), b?=?12.1863(14), c?=?9.0076(10) Å, β?=?105.045(2)°, V?=?649.9(1) ų, Z?=?2. Eight strongest reflections of the powder XRD pattern are [d,Å-I(hkl)]: 5.386–34(110); 4.312–46(002); 4.240–33(120); 4.085–100(012, 10–2); 3.685–85(031), 3.041–45(040, 112), 2.808–31(013, 20–2, 122), 2.368–34(13–3, 21–3, 033). Nickelpicromerite (single-crystal X-ray data, R?=?0.028) is isostructural to other picromerite-group minerals and synthetic Tutton’s salts. Its crystal structure consists of [Ni(H₂O)₆]²⁺ octahedra linked to (SO₄)^2? tetrahedra via hydrogen bonds. K⁺ cations are coordinated by eight anions. Nickelpicromerite is the product of alteration of primary sulfide minerals and the reaction of the acid Ni-sulfate solutions with biotite.     

High-pressure X-ray diffraction and Raman spectroscopy of CaFe<Subscript>2</Subscript>O<Subscript>4</Subscript>-type β-CaCr<Subscript>2</Subscript>O<Subscript>4</Subscript>

In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopic studies of orthorhombic CaFe₂O₄-type β-CaCr₂O₄ chromite were carried out up to 16.2 and 32.0 GPa at room temperature using multi-anvil apparatus and diamond anvil cell, respectively. No phase transition was observed in this study. Fitting a third-order Birch–Murnaghan equation of state to the P–V data yields a zero-pressure volume of V ₀ = 286.8(1) ų, an isothermal bulk modulus of K ₀ = 183(5) GPa and the first pressure derivative of isothermal bulk modulus K ₀′ = 4.1(8). Analyses of axial compressibilities show anisotropic elasticity for β-CaCr₂O₄ since the a-axis is more compressible than the b- and c-axis. Based on the obtained and previous results, the compressibility of several CaFe₂O₄-type phases was compared. The high-pressure Raman spectra of β-CaCr₂O₄ were analyzed to determine the pressure dependences and mode Grüneisen parameters of Raman-active bands. The thermal Grüneisen parameter of β-CaCr₂O₄ is determined to be 0.93(2), which is smaller than those of CaFe₂O₄-type CaAl₂O₄ and MgAl₂O₄.     

Elastic and thermoelastic properties of synthetic Ca<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript> (åkermanite) and Ca<Subscript>2</Subscript>ZnSi<Subscript>2</Subscript>O<Subscript>7</Subscript> (hardystonite)

Elastic and thermoelastic constants of large single crystals of Ca₂MgSi₂O₇ and Ca₂ZnSi₂O₇ have been derived from ultrasonic resonance frequencies of plane-parallel plates and their shift upon variation of temperature, respectively. In addition, coefficients of thermal expansion and dielectric constants were determined. Both species possess quite similar properties. As observed in other isotypic magnesium and zinc compounds, the mean elastic stiffness and the deviation from the Cauchy relations are significantly larger in the zinc compound, due to a covalent contribution of the Zn–O bond. Positive thermoelastic constants T₄₄ and T₆₆ in Ca₂MgSi₂O₇ allow temperature-independent ultrasonic generators and oscillators to be manufactured.     

Thermophysical properties of the α–β–γ polymorphs of Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript>: a computational study

Thermophysical properties of the various polymorphs (i.e. α-, β- and γ) of Mg₂SiO₄ were computed with the CRYSTAL06 code within the framework of CO-LCAO-GTF approach by using the hybrid B3LYP density functional method. Potential wells were calculated through a symmetry preserving, variable cell-shape structure relaxation procedure. Vibrational frequencies were computed at the long-wavelength limit corresponding to the center of the Brillouin zone (k → 0). Thermodynamic properties were estimated through a semiclassical approach that combines B3LYP vibrational frequencies for optic modes and the Kieffer’s model for the dispersion relation of acoustic modes. All computed values except volume (i.e. electronic energy, zero point energy, optical vibrational modes, thermal corrections to internal energy, standard state enthalpy and Gibbs free energy of reaction, bulk modulus and its P and T derivatives, entropy, C _V, C _P) are consistent with available experimental data and/or reasonable estimates. Volumes are slightly overestimated relative to those determined directly by X-ray diffraction. A set of optimized volumetric properties that are consistent with the other semiclassical properties of the phases α, β and γ have been derived by optimization procedure such that the calculated boundaries for the α/β and β/γ equilibria have the best overall agreement with the experimental data for these transitions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

X-ray single-crystal and Raman study of (Na<Subscript>0.86</Subscript>Mg<Subscript>0.14</Subscript>)(Mg<Subscript>0.57</Subscript>Ti<Subscript>0.43</Subscript>)Si<Subscript>2</Subscript>O<Subscript>6</Subscript>, a new pyroxene synthesized at 7 GPa and 1700 °C

A new pyroxene with formula (Na_0.86Mg_0.14)(Mg_0.57Ti_0.43)Si₂O₆, synthesized in a high-pressure toroidal ‘anvil-with-hole’ apparatus at P = 7 GPa and T = 1700 °C, was characterized by X-ray single-crystal diffraction and Raman spectroscopy. The compound was found to be monoclinic (R1 = 2.56 %), space group C2/c, with lattice parameters a = 9.687(2), b = 8.814(1), c = 5.290(1) Å, β = 107.853(2)°, V = 430.08(1) ų. The coexistence of Mg and Ti⁴⁺ at the M1 site does not induce strong modifications either to the M1 site or to the adjacent M2 site. The Raman spectrum of synthetic Na–Ti-pyroxene was obtained for the first time and compared with that of Mg₂Si₂O₆ (with very low concentrations of Na and Ti). The structural characterization of the Na–Ti–Mg-pyroxene is important, because the study of its thermodynamic constants provides new constraints on thermobarometry of the upper mantle assemblages.     

Kamarizaite,Fe<Stack><Subscript>3</Subscript><Superscript>3+</Superscript></Stack>(AsO<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)<Subscript>3</Subscript> · 3H<Subscript>2</Subscript>O,a new mineral species,arsenate analogue of tinticite

Kamarizaite, a new mineral species, has been identified in the dump of the Kamariza Mine, Lavrion mining district, Attica Region, Greece, in association with goethite, scorodite, and jarosite. It was named after type locality. Kamarizaite occurs as fine-grained monomineralic aggregates (up to 3 cm across) composed of platy crystals up to 1 μm in size and submicron kidney-shaped segregations. The new mineral is yellow to beige, with light yellow streak. The Mohs hardness is about 3. No cleavage is observed. The density measured by hydrostatic weighing is 3.16(1) g/cm³, and the calculated density is 3.12 g/cm³. The wavenumbers of absorption bands in the IR spectrum of kamarizaite are (cm^?1; s is strong band, w is weak band): 3552, 3315s, 3115, 1650w, 1620w, 1089, 911s, 888s, 870, 835s, 808s, 614w, 540, 500, 478, 429. According to TG and IR data, complete dehydration and dehydroxylation in vacuum (with a weight loss of 15.3(1)%) occurs in the temperature range 110–420°C. Mössbauer data indicate that all iron in kamarizaite is octahedrally coordinated Fe³⁺. Kamarizaite is optically biaxial, positive: n _min = 1.825, n _max = 1.835, n _mean = 1.83(1) (for a fine-grained aggregate). The chemical composition of kamarizaite (electron microprobe, average of four point analyses) is as follows, wt %: 0.35 CaO, 41.78 Fe₂O₃, 39.89 As₂O₅, 1.49 SO₃, 15.3 H₂O (from TG data); the total is 98.81. The empirical formula calculated on the basis of (AsO₄,SO₄)₂ is Ca_0.03Fe _2.86 ³⁺ (AsO₄)_1.90(SO₄)_0.10(OH)_2.74 · 3.27H₂O. The idealized formula is Fe ₃ ³⁺ (AsO₄)₂(OH)₃ · 3H₂O. Kamarizaite is an arsenate analogue of orthorhombic tinticite, space group Pccm, Pcc2, Pcmm, Pcm2₁, or Pc2m; a = 21.32(1), b = 13.666(6), c =15.80(1) Å, V= 4603.29(5) ų, Z= 16. The strongest reflections of the X-ray powder diffraction pattern [\(\bar d\), Å (I, %) (hkl)] are: 6.61 (37) (112, 120), 5.85 (52) (311), 3.947 (100) (004, 032, 511), 3.396 (37) (133, 431), 3.332 (60) (314), 3.085 (58) (621, 414, 324). The type material of kamarizaite is deposited in the Mineralogical Collection of Technische Universität Bergakademie Freiberg, Germany, inventory number 82199.     

Calcioolivine, γ-Ca<Subscript>2</Subscript>SiO<Subscript>4</Subscript>, an old and New Mineral species

Calcioolivine has been included into the MDI mineral database in the list of grandfathered minerals. Its history, together with related artificial compounds, is extremely complex: various minerals and compounds received this name, including natural orthorhombic Ca orthosilicate. In this paper, the crystal structure and properties of natural calcioolivine are described for the first time. The new mineral has been found at Mt. Lakargi, Upper Chegem Plateau, the northern Caucasus, Kabarda-Balkaria Republic, Russia. It has been identified in skarnified, primary carbonate xenoliths entrained by middle to late Pliocene silicic ignimbrites of the Upper Chegem caldera. These xenoliths of a few centimeters to a few meters in size are located close to the volcanic vent. Calcioolivine rims relics of larnite and occurs as relict grains among crystals of spurrite, rondorfite, wadalite or secondary hillebrandite, afwillite, thaumasite, and ettringite. Hillebrandite is the major product of alteration of calcioolivine; larnite is relatively more resistant to low-temperature alteration. Spurrite, larnite, tilleyite, kilchoanite, cuspidine, wadalite, rondorfite, reinhardbraunsite, lakargiite (CaZrO₃), members of ellestadite series, afwillite, ettringite, katoite, and thaumasite are associated minerals. It is inferred that calcioolivine has been produced as a result of interaction of host carbonate rocks in xenoliths with volcanic lava and gases during eruption. The name calcioolivine was approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, September 6, 2007 (no. 07-B).     

Thermal expansion of hydrated six-coordinate silicon in thaumasite,Ca<Subscript>3</Subscript>Si(OH)<Subscript>6</Subscript>(CO<Subscript>3</Subscript>)(SO<Subscript>4</Subscript>)·12H<Subscript>2</Subscript>O

Thaumasite, Ca₃Si(OH)₆(CO₃)(SO₄)12H₂O, occurs as a low-temperature secondary alteration phase in mafic igneous and metamorphic rocks, and is recognized as a product and indicator of sulfate attack in Portland cement. It is also the only mineral known to contain silicon in six-coordination with hydroxyl (OH)^? that is stable at ambient P–T conditions. Thermal expansion of the various components of this unusual structure has been determined from single-crystal X-ray structure refinements of natural thaumasite at 130 and 298 K. No phase transitions were observed over this temperature range. Cell parameters at room temperature are: a= 11.0538(6) Å, c=10.4111(8) Å and V=1101.67(10) ų, and were measured at intervals of about 50 K between 130 and 298 K, resulting in mean axial and volumetric coefficients of thermal expansion (×10^?5K^?1); α _a =1.7(1), α _c =2.1(2), and α _V =5.6(2). Although the unit cell and ^VIIICaO₈ polyhedra show significant positive thermal expansion over this temperature range, the silicate octahedron, sulfate tetrahedron, and carbonate group show zero or negative thermal expansion, with α _V (^VISiO₆) = ?0.6 ± 1.1, α _V (^IVSO₄)=?5.8 ± 1.4, and α _R (C–O)= 0.0 ± 1.8 (×10^?5 K^?1). Most of the thermal expansion is accommodated by lengthening of the R(O...O) hydrogen bond distances by on average 5σ, although the hydrogen bonds involving hydroxyl sites on ^VISi expand twice as much as those on molecular water, causing the [Ca₃Si(OH)₆(H₂O)₁₂]⁴⁺ columns to expand in diameter more than they move apart over this temperature range. The average Si–OH bond length of the six-coordinated Si atom 〈R(^VISi–OH)〉 in thaumasite is 1.783(1) Å, being about 0.02 Å (?20σ) shorter than ^VISi–OH in the dense hydrous magnesium silicate, phase D, MgSi₂H₂O₆.     

Mangazeite,Al<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)(OH)<Subscript>4</Subscript> · 3H<Subscript>2</Subscript>O,a new mineral species

Mangazeite, a new mineral species, has been found at the Mangazeya silver deposit (300 km east of the Lena River, 65°43′40″ N and 130°20′ E) in eastern Yakutia (Sakha Republic, Siberia, Russia). The new mineral was described from fractured, sericitized, and pyritized granodiorite adjacent to a quartz-arsenopyrite vein. Associated minerals are gypsum and chlorite. The new mineral occurs as radial fibrous segregations of thin lamellar crystals. The size of the fibers does not exceed 40 μm in length and 1 μm across. The mineral is white, with a white streak and a vitreous luster. Mangazeite is transparent in isolated grains. No fluorescence is observed. The Mohs hardness is 1–2. The calculated density is 2.15 g/cm³. The new mineral is biaxial; its optical character was not determined; α = 1.525(9), β was not measured, and γ = 1.545(9). The average chemical composition is as follows (wt %): Al₂O₃ 36.28, SO₃ 28.81, H₂O⁺ 34.35, total 99.44, H₂O^? 9.27. The H₂O^? content was neither included in the total nor used in formula calculation. The empirical formula is Al_1.99(SO₄)_1.01(OH)_3.94 · 3.37H₂O. The simplified formula is Al₂(SO₄)(OH)₄ · 3H₂O. The theoretical chemical composition calculated from this formula is (wt %) Al₂O₃ 37.47, SO₃ 29.42, H₂O 33.11, total 100.00. The new mineral is triclinic; the unit cell parameters refined from X-ray powder diffraction data are a = 8.286(5), b = 9.385(5), c = 11.35(1) Å, α = 96.1(1), β = 98.9(1), γ = 96.6(1)°, and Z = 4. The strongest lines in the X-ray powder diffraction pattern (d(I, %)) are 8.14(19), 7.59(49), 7.16(46), 4.258(100), 4.060(48), and 3.912(43). Mangazeite is supergene in origin and crystallized in a favorable aluminosilicate environment in the presence of sulfate ion due to pyrite oxidation.     

Mineral CuFe<Subscript>2</Subscript>S<Subscript>4</Subscript> from sulfide Copper–Nickel ores of the Lovnoozero deposit,Kola Peninsula

The unnamed mineral CuFe₂S₄ has been found from sulfide Cu–Ni ores of the Lovnoozero deposit in the Kola Peninsula, Russia. It occurs in norite composed of orthopyroxene (bronzite), Ca-rich plagioclase (66% An), pargasite, and phlogopite. The last two minerals are replaced by talc, chlorite and carbonates. Monoclinic pyrrhotite, pentlandite, chalcopyrite, and pyrite are associated ore minerals. Phase CuFe₂S₄ is enclosed predominantly in chalcopyrite, probably replacing it, and occurs in later carbonate veinlets together with redeposited sulfides. It is light yellow with a brownish tint and metallic luster. The Mohs hardness is 5–5.5; VHN 654 ± 86 kgs/mm². Density (calc.) = 4.524 g/cm³. The mineral is anisotropic, internal reflections are absent. Reflectance values (λ, nm R′ _g and R′ _p %) are: 440 30.3 29.5, 500 43.7 42.8, 560 50.9 49.6, 620 52.4 51.2, 640 52.6 51.4, 680 52.8 51.6, 700 52.7 51.4. CuFe₂S₄ is monoclinic, a = 6.260(4), b = 5.39(1), c = 13.19(1) Å, β = 94.88(7)°, V = 443(1) ų, Z = 4. The strongest reflections in the powder diffraction pattern are [d, Å (I) (hkl)]: 4.150 (10) (012), 3.559 (4) (\(11\bar 2\)), 3.020 (4) (\(10\bar 4\)), 2.560 (3) (\(21\bar 2\)), 2.500 (3) (\(10\bar 5\)), 2.340 (3) (\(12\bar 2\)), 1.817 (3) (215), 1.489 (3) (402). The chemical composition is as follows, wt %: 20.44 Cu, 35.85 Fe, 0.65 Ni, 0.14 Co, 43.15 S, total is 100.23. The empirical formula calculated on the basis of 7 atoms is Cu_0.969(Fe_1.934Ni_0.034Co_0.007)_1.975S_4.056. According to its mode of occurrence, the mineral was formed as a result of low temperature processes involving metamorphic hydrothermal solutions.     

Yegorovite,Na<Subscript>4</Subscript>[Si<Subscript>4</Subscript>O<Subscript>8</Subscript>(OH)<Subscript>4</Subscript>]·7H<Subscript>2</Subscript>O,a new mineral from the Lovozero alkaline pluton,Kola Peninsula

A new mineral, yegorovite, has been identified in the late hydrothermal, low-temperature assemblage of the Palitra hyperalkaline pegmatite at Mt. Kedykverpakhk, Lovozero alkaline pluton, Kola Peninsula, Russia. The mineral is intimately associated with revdite and megacyclite, earlier natrosilite, microcline, and villiaumite. Yegorovite occurs as coarse, usually split prismatic (up to 0.05 × 0.15 × 1 mm) or lamellar (up to 0.05 × 0.7 × 0.8 mm) crystals. Polysynthetic twins and parallel intergrowths are typical. Mineral individuals are combined in bunches or chaotic groups (up to 2 mm); radial-lamellar clusters are less frequent. Yegorovite is colorless, transparent with vitreous luster. Cleavage is perfect parallel to (010) and (001). Fracture is splintery; crystals are readily split into acicular fragments. The Mohs hardness is ～2. Density is 1.90(2) g/cm³ (meas) and 1.92 g/cm³ (calc). Yegorovite is biaxial (?), with α = 1.474(2), β = 1.479(2), and γ = 1.482(2), 2V _meas > 70°, 2V _calc = 75°. The optical orientation is X ∧ a ～ 15°, Y = c, Z = b. The IR spectrum is given. The chemical composition determined using an electron microprobe (H₂O determined from total deficiency) is (wt %): 23.28 Na₂O, 45.45 SiO₂, 31.27 H₂O_calc; the total is 100.00. The empirical formula is Na_3.98Si_4.01O_8.02(OH)_3.98 · 7.205H₂O. The idealized formula is Na₄[Si₄O₈(OH)₄] · 7H₂O. Yegorovite is monoclinic, space group P2₁/c. The unit-cell dimensions are a = 9.874, b= 12.398, c = 14.897 Å, β = 104.68°, V = 1764.3 ų, Z = 4. The strongest reflections in the X-ray powder pattern (d, Å (I, %)([hkl]) are 7.21(70)[002], 6.21(72)[012, 020], 4.696(44)[022], 4.003(49)[211], 3.734(46)[\(\bar 2\) 13], 3.116(100)[024, 040], 2.463(38)[\(\bar 4\)02, \(\bar 2\)43]. The crystal structure was studied by single-crystal method, R _hkl = 0.0745. Yegorovite is a representative of a new structural type. Its structure consists of single chains of Si tetrahedrons [Si₄O₈(OH)₄]∞ and sixfold polyhedrons of two types: [NaO(OH)₂(H₂O)₃] and [NaO(OH)(H₂O)₄] centered by Na. The mineral was named in memory of Yu. K. Yegorov-Tismenko (1938–2007), outstanding Russian crystallographer and crystallochemist. The type material of yegorovite has been deposited at the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow.     

Fluid–mineral reactions and melting of orthopyroxene–cordierite–biotite gneiss in the presence of H<Subscript>2</Subscript>O-CO<Subscript>2</Subscript>-NaCl and H<Subscript>2</Subscript>O-CO<Subscript>2</Subscript>-KCl fluids under parameters of granulite-facies metamorphism

Reactions and partial melting of peraluminous rocks in the presence of H₂O-CO₂–salt fluids under parameters of granulite-facies metamorphism were modeled in experiments on interaction between orthopyroxene–cordierite–biotite–plagioclase–quartz metapelite with H₂O, H₂O-CO₂, H₂O-CO₂-NaCl, and H₂O-CO₂-KCl fluids at 600 MPa and 850°C. Rock melting in the presence of H₂O and equimolar H₂O-CO₂ fluids generates peraluminous (A/CNK¹ > 1.1) melts whose composition corresponds to magnesian calcic or calc–alkaline S-type granitoids. The melts are associated with peritectic phases: magnesian spinel and orthopyroxene containing up to 9 wt % Al₂O₃. In the presence of H₂O-CO₂-NaCl fluid, cordierite and orthopyroxene are replaced by the association of K-Na biotite, Na-bearing gedrite, spinel, and albite. The Na₂O concentrations in the biotite and gedrite are functions of the NaCl concentrations in the starting fluid. Fluids of the composition H₂O-CO₂-KCl induce cordierite replacement by biotite with corundum and spinel and by these phases in association with potassium feldspar at X _KCl = 0.02 in the fluid. When replaced by these phases, cordierite is excluded from the melting reactions, and the overall melting of the metapelite is controlled by peritectic reactions of biotite and orthopyroxene with plagioclase and quartz. These reactions produce such minerals atypical of metapelites as Ca-Na amphibole and clinopyroxene. The compositions of melts derived in the presence of salt-bearing fluids are shifted toward the region with A/CNK < 1.1, as is typical of so-called peraluminous granites of type I. An increase in the concentrations of salts in the fluids leads to depletion of the melts in Al₂O₃ and CaO and enrichment in alkalis. These relations suggest that the protoliths of I-type peraluminous granites might have been metapelites that were melted when interacting with H₂O-CO₂-salt fluids. The compositions of the melts can evolve from those with A/CNK > 1.1 (typical of S-type granites) toward those with A/CNK = 1.0–1.1 in response to an increase in the concentrations of alkali salts in the fluids within a few mole percent. Our experiments demonstrate that the origin of new mineral assemblages in metapelite in equilibrium with H₂O-CO₂-salt fluids is controlled by the activities of alkaline components, while the H₂O and CO₂ activities play subordinate roles. This conclusion is consistent with the results obtained by simulating metapelite mineral assemblages by Gibbs free energy minimization (using the PERPE_X software), as shown in log(\({a_{{H_2}O}}\))–log(\({a_{N{a_2}O}}\)) and log(\({a_{{H_2}O}}\))–log(\({a_{{K_2}O}}\)) diagrams.     

Optical spectroscopic study of synthetic NaScSi<Subscript>2</Subscript>O<Subscript>6</Subscript>–CaNiSi<Subscript>2</Subscript>O<Subscript>6</Subscript> pyroxenes at normal and high pressures

Six synthetic NaScSi₂O₆–CaNiSi₂O₆ pyroxenes were studied by optical absorption spectroscopy. Five of them of intermediate (Na_1−x , Ca _x )(Sc_1−x , Ni _x )Si₂O₆ compositions show spectra typical of Ni²⁺ in octahedral coordination, more precise Ni²⁺ at the M1 site of the pyroxene structure. The common feature of all spectra is three broad absorption bands with maxima around 8,000, 13,000 and 24,000 cm⁻¹ assigned to ³ A _2g → ³ T _2g, ³ A _2g → ³ T _1g and →³ T _1g (³ P) electronic spin-allowed transitions of ^VINi²⁺. A weak narrow peak at ∼14,400 cm⁻¹ is assigned to the spin-forbidden ³ A _2g → ¹ T _2g (¹ D) transition of Ni²⁺. Under pressure the spin-allowed bands shift to higher energies and change in intensity. The octahedral compression modulus, calculated from the shift of the ³ A _2g → ³ T _2g band in the (Na_0.7Ca_0.3)(Sc_0.7Ni_0.3)Si₂O₆ pyroxene is evaluated as 85±20 GPa. The Racah parameter B of Ni²⁺(M1) is found gradually changing from ∼919 cm⁻¹ at ambient pressure to ∼890 cm⁻¹ at 6.18 GPa. The Ni end-member pyroxene [(Ca_0.93 Ni_0.07)NiSi₂O₆] has a spectrum different from all others. In addition to the above mentioned bands of Ni²⁺(M1) it displays several new relatively intense and broad extra bands, which were attributed to electronic transitions of Ni²⁺ at the M2 site. In difference to CaO₈ polyhedron geometry of an eightfold coordination, Ni²⁺(M2)O₈ polyhedra are assumed to be relatively large distorted octahedra. Due to different distortions and different compressibilities of the M1 and M2 sites the Ni²⁺(M1)- and Ni²⁺(M2)-bands display rather different pressure-induced behaviors, becoming more resolved in the high-pressure spectra than in that measured at atmospheric pressure. The octahedral compression modulus of Ni²⁺(M1) in this end-member pyroxene is evaluated as 150 ± 25 GPa, which is noticeably larger than in Ni_0.3 pyroxene. This is due to a smaller size and, thus, a stiffer character of Ni²⁺(M1)O₆ octahedron in the (Ca_0.93Ni_0.07)NiSi₂O₆ pyroxene compared to (Na_0.7Ca_0.3)(Sc_0.7Ni_0.3)Si₂O₆.