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Three samples of the skarn mineral rustumite Ca10(Si2O7)2(SiO4)(OH)2Cl2, space group C2/c, a ≈7.6, b ≈ 18.5, c ≈ 15.5 Å, β ≈ 104°, with variable OH, Cl, F content were investigated by electron microprobe, single-crystal X-ray structure refinements, and Raman spectroscopy. "Rust1_LCl" is a low chlorine rustumite Ca10(Si2O7)2(SiO4)(OH1.88F0.12)(Cl1.28,OH0.72) from skarns associated with the Rize batholith near Ikizedere, Turkey. "Rust2_F" is a F-bearing rustumite Ca10(Si2O7)2(SiO4)(OH1.13F0.87)(Cl1.96OH0.04) from xenoliths in ignimbrites of the Upper Chegem Caldera, Northern Caucasus, Russia. "Rust3_LCl_F" represents a low-Cl, F-bearing rustumite Ca10(Si2O7)2(SiO4)0.87(H4O4)0.13](OH1.01F0.99)(Cl1.00 OH1.00) from altered merwinite skarns of the Birkhin massif, Baikal Lake area, Eastern Siberia, Russia. Rustumite from Birkhin massif is characterized by a significant hydrogarnet-like or fluorine substitution at the apices of the orthosilicate group, leading to specific atomic displacements. The crystal structures including hydrogen positions have been refined from single-crystal X-ray data to R1 = 0.0205 (Rust1_LCl), R1 = 0.0295 (Rust2_F), and R1 = 0.0243 (Rust3_LCl_F), respectively. Depletion in Cl and replacement by OH is associated with smaller unit-cell dimensions. The substitution of OH by F leads to shorter hydrogen bonds O-H⋅⋅⋅F instead of O-H⋅⋅⋅OH. Raman spectra for all samples have been measured and confirm slight strengthening of the hydrogen bonds with uptake of F.This study discusses the complex crystal chemistry of the skarn mineral rustumite and may provide a wider understanding of the chemical reactions related to contact metamorphism of limestones. [ABSTRACT FROM AUTHOR]

Members of the edgrewite Ca9(SiO4)4F2-hydroxyledgrewite Ca9(SiO4)4(OH)2 series, structural analogues of clinohumite-hydroxylclinohumite series, Mg9(SiO4)4(F,OH)2, were discovered in xenoliths of carbonate-silicate rock altered to skarn within ignimbrites of the Upper Chegem volcanic structure, Kabardino-Balkaria, Northern Caucasus, Russia. The new minerals occur sparingly in zones containing bultfonteinite, hillebrandite, jennite, and chegemite, as well as rare relics of larnite and rondorfite enclosed in a matrix of hydroxylellestadite. Edgrewite and hydroxyledgrewite are largely altered to jennite in places with admixed zeophyllite and trabzonite, and are preserved as elongate relics mostly 0.1-0.4 mm long in the central part of atoll-like pseudomorphs. The new minerals form a solid-solution series Ca9(SiO4)4(F,OH)2, in which the content of the edgrewite end-member Ca9(SiO4)4F2 ranges from 74% (F = 3.64 wt%) to 31% (F = 1.52 wt%). Structure refinement of crystals containing 51% and 37% of the edgrewite end-member gave, respectively, R1 = 3.03%, space group P21/b11 (no. 14), Z = 2, a = 5.06870(10), b = 11.35790(10), c = 15.4004(2) Å, α = 100.5980(10)°, V = 871.47(3) ų; and R1 = 1.61%, space group P21/b11 (no. 14), Z = 2, a = 5.06720(10), b = 11.35450(10), c = 15.3941(2) Å, α = 100.5870(10)°, and V = 870.63(2) ų. Minerals of the edgrewite-hydroxyledgrewite series are colorless, optically biaxial (+), 2Vmeas = 80(5)°; 2Vcalc = 78.7°; dispersion r > v, medium; orientation: Z = a, X ^ c = 12(2)°; edgrewite: α = 1.621(2), β = 1.625(2), γ = 1.631(2); hydroxyledgrewite: α = 1.625(2), β = 1.629(2), γ = 1.635(2) (589 nm). The micro-hardness VHN50 = 352-366 kg/mm² corresponds to the Mohs scale of 5.5-6. 5. FTIR spectra of edgrewite and hydroxyledgrewite show resolved bands at (edgrewite/hydroxyledgrewite, cm-1): 3558 and 3551 and 3543/3554, absent/3486, 1075/1075, 996/996, 980/982, 934/933, 917/918, 904/903, 890/884, 864/864, 842/842, 818/820. Raman spectra are characterized by the following bands (edgrewite/hydroxyledgrewite, cm-1) at: 921/923, 889/890, 839/840, and 815/814 (SiO4 stretching), at: 556/559, 527/527, 423/419, 406/404, and 394/394 (SiO4 bending), 309/295, 269/256, and 163/166 (CaO6). In the OH stretching region three bands are noted at 3554, 3547, and 3540 cm-1 for edgrewite and two - 3550 and 3475 cm-1 for hydroxyledgrewite confirming the corresponding IR spectra. The major difference in Raman and IR spectra of edgrewite and hydroxyledgrewite is the presence of two resolved peaks in the OH stretching region at ca. 3550 and 3480 cm-1 for hydroxyledgrewite [ABSTRACT FROM AUTHOR]

The new mineral pavlovskyite Ca8(SiO4)2(Si3O10) forms rims together with dellaite Ca6(Si2O7)(SiO4)(OH)2 around galuskinite Ca7(SiO4)3CO3 veins cutting calcio-olivine skarns in the Birkhin gabbro massif. In addition, skeletal pavlovskyite occurs in cuspidine zones of altered carbonate xenoliths in the ignimbrites of the Upper Chegem caldera (North Caucasus). The synthetic analog of pavlovskyite has been synthesized before and is known from cement-like materials. Isotypic to pavlovskyite is the synthetic germanate analog Ca8(GeO4)2(Ge3O10). The crystal structure of pavlovskyite, space group Pbcn, a = 5.0851(1), b = 11.4165(3), c = 28.6408(8) Å, V = 1662.71(7) ų, Z = 4, has been refined from X-ray single-crystal data to R1 = 3.87%. The new colorless mineral has a Mohs hardness of 6--6.5, biaxial (-), α = 1.656(2), β = 1.658(2), γ = 1.660(2) (589 nm), 2V (meas) = 80(5)°, 2V (calc) = 89.9°, medium dispersion: r > v, optical orientation: X = b, Y = c, Z = a.For comparison with pavlovskyite, the crystal structure of kilchoanite Ca6(SiO4)(Si3O10) from the Birkhin massif [space group I2cm, a = 11.4525(2), b = 5.0867(1), c = 21.996(3) Å, V = 1281.40(4) ų, Z = 4] has been refined from single-crystal X-ray data to R1 = 2.00%.Pavlovskyite represents a 1:1 member of a polysomatic series with calcio-olivine γ-Ca2SiO4 and kilchoanite Ca6(SiO4)(Si3O10) as end-member modules. The structure is characterized by strongly folded trisilicate units (Si3O10) interwoven with a framework of CaO6 and CaO8 polyhedra. Olivine-like slices with orthosilicate groups are interstratified with the characteristic trisilicate module of Ca4(Si3O10) composition. Although the optical properties of pavlovskyite and kilchoanite are similar, both minerals can be distinguished by chemical analyses (different Ca/Si ratio), X-ray diffraction, and Raman spectroscopy. The new mineral is named after V.E. Pavlovsky (1901--1982), an outstanding geologist in the area of Eastern Siberia, in particular of the Baikal region. [ABSTRACT FROM AUTHOR]

The new mineral vorlanite, (CaU6+)O4, Dcalc = 7.29 g/cm³, H = 4-5, VHN10 = 360 kg/mm², was found near the top of Mt. Vorlan in a calcareous skarn xenolith in ignimbrite of the Upper Chegem caldera the Northern Caucasus, Kabardino-Balkaria, Russia. Vorlanite occurs as aggregates of black platy crystals up to 0.3 mm long with external symmetry 3̄m. The strongest powder diffraction lines are [d(Å)/(hkl)]: 3.107/(111), 2.691/(200), 1.903/(220), 1.623/(311), 1.235/(331), 1.203/(420), 1.098/(422), 0.910/(531). Single-crystal X-ray study gives isometric symmetry, space group Fm3̄m, a = 5.3813(2) Å, V = 155.834(10) ų, and Z = 2. X-ray photoelectron spectroscopy indicate that all U in vorlanite hexavalent. The mineral is isostructural with fluorite and uraninite (U4+O2). In contrast to synthetic ombohedral CaUO4, and most U6+ minerals, the U6+ cations in vorlanite are present as disordered uranyl ions. [8]Ca2+ and [8]U6+ are disordered over a single site with average M-O = 2.33 Å. Vorlanite is believed to be a pseudomorphic replacement of originally rhombohedral CaUO4. We assume that this rhombohedral phase transformed by radiation damage to cubic CaUO4 (vorlanite). The new mineral is associated with larnite, chegemite, reinhardbraunsite, lakargiite, rondorfite, and wadalite, which are indicative of high-temperature formation (>800 °C) at shallow depth. [ABSTRACT FROM AUTHOR]

Garnet from an aposkarn achtarandite-bearing rodingite-like rock in Sakha-Yakutia, Russia, has a Sc content close to 6 wt% Sc2O3 (∼0.45 apfu). The scandian garnet is a relict mineral from a high-temperature, shallow-level melilite skarn. Structural and electron microprobe data for a crystal of the scandian garnet with cell parameter a = 12.331(1) Å, Ia3̅d allows refinement of the structural formula (Ca2.97Mg0.02Y0.01)Σ3 (Fe0.6633+Zr0.584Ti0.2944+Sc0.153 Cr0.152Mg0.094Fe0.042+Hf0.008V0.003) Σ2(Si1.898Al0.420Ti0.3594+ Fe0.3233+)Σ3O12. Investigation of the composition of many of the scandian garnets reveals the existence of a solid-solution between kimzeyite-schorlomite Ca3(Zr,Ti)2(Al,Fe)2SiO12 and the scandium analog of andradite Ca3Sc2Si3O12. This is the first report of a natural scandian garnet. [ABSTRACT FROM AUTHOR]

A new Sn-rich garnet, toturite Ca3Sn2Fe2SiO12, occurs as an accessory mineral in high-temperature altered carbonate-silicate xenoliths in ignimbrite of the Upper Chegem structure in the Northern Caucasus, Kabardino-Balkaria, Russia. The empirical formula of toturite from the holotype sample is (Ca2.989Fe0.0112+)Σ3(Sn1.4634+Sb0.3255+Ti0.1934+Zr0.013Mg0.003Nb0.0025+Cr0.001)Σ2(Fe1.6333+Al0.609Si0.552Ti0.1664+Fe0.0392+V0.0015+)Σ3O12. The mineral forms thin regular growth zones and irregular spots in the Fe3+-dominant analog of kimzeyite. Toturite is cubic, Ia3̄d, a ≈ 12.55 Å, as is confirmed by electron backscatter diffraction (EBSD) data. The strongest lines of the calculated powder diffraction pattern are [d, Å (hkl) I]: 2.562 (422) 100, 1.677 (642) 91, 3.138 (400) 74, 4.437 (220) 67, 1.146 (10.4.2) 31, 1.046 (884) 25, 1.984 (620) 23. Raman spectra of toturite are analogous to those of kimzeyite and shows the following diagnostic bands (cm-1): 244, 301, 494, 497, 575, 734. The association of toturite with larnite, rondorfite, wadalite, magnesioferrite, lakargiite, and cuspidine indicates a high temperature (>800 °C) of formation. The mineral name is given after the Totur River situated in Eltyubyu village, also Totur is the name of a Balkarian god. [ABSTRACT FROM AUTHOR]

Two new antimonian garnets--bitikleite-(SnAl) Ca3SbSnAl3O12 and bitikleite-(ZrFe) Ca3SbZrFe3O12--have been found as accessory minerals in the cuspidine zone of high-temperature skarns in a carbonate-silicate xenolith at the contact with ignimbrites within the Upper Chegem structure in the Northern Caucasus, Kabardino-Balkaria, Russia. The bitikleite series forms a solid solution with garnets of the kimzeyite-schorlomite and toturite type. Antimony-garnets form crystals up to 50 µm across containing kimzeyite cores and thin subsequent zones of complex lakargiite-tazheranite-kimzeyite pseudomorphs after zircon. Bitikleite-(SnAl) has a = 12.5240(2) Å, V = 1964.40(3) ų and bitikleite-(ZrFe) has a = 12.49 Å, V = 1948.4 ų (Ia3̅d, Z = 8). The strongest powder diffraction lines of bitikleite-(SnAl) are [d, Å (hkl)]: 4.407 (220), 3.118 (440), 2.789 (420), 2.546 (422), 1.973 (620), 1.732 (640), 1.668 (642), and 1.396 (840). The strongest calculated powder diffraction lines of bitikleite-(ZrFe) are [d, Å (hkl)]: 4.416 (220), 3.123 (440), 2.793 (420), 2.550 (422), 1.975 (620), 1.732 (640), 1.669 (642), and 1.396 (840). The Raman spectra of bitikleite garnets are similar to the spectra of kimzeyite and toturite. Larnite, rondorfite, wadalite, magnesioferrite, tazheranite, lakargiite, kimzeyite, and toturite associated with bitikleite garnets are typical of high-temperature (>800 °C) formation. [ABSTRACT FROM AUTHOR]

Pertsevite-(OH), end-member formula Mg2(BO3)(OH), is a new mineral found in a ludwigite-kotoite magnesian skarn from the Snezhnoye deposit in Sakha-Yakutia Republic, Russia. The Commission on New Minerals, Nomenclature and Classification, IMA (IMA 2008-060) has approved the mineral and the mineral name. Moreover, the Chairman of the CNMNC agreed to renaming pertsevite to pertsevite-(F). The two minerals constitute the pertsevite series with the general formula Mg2(BO3)1-x (SiO4)x(OH,F)1-x, where x = 0.1-0.3. Pertsevite-(OH) is biaxial: 2Vz = 55-65°(meas), 2Vz = 75°(calc); α = 1.611(1), β = 1.623(1), γ = 1.644(1)°; X = b, Y = c, Z = a. It is associated with kotoite, szaibelyite, ludwigite-azoproite, clinohumite, hydroxylclinohumite, forsterite, chondrodite, calcite, REE-bearing sakhaite, sphalerite, and goethite. Ion microprobe analyses of pertsevite-(OH) using secondary ion mass spectrometry gave B, F, and H contents consistent with B and F contents determined by electron microprobe analyses (EMPA), and with OH contents calculated from EMPA data, confirming that OH/F ratio > 1 in pertsevite-(OH). Pertsevite-(OH) is orthorhombic, with space group Pnma. Cell dimensions refined from X-ray powder diffraction data are as follows: a = 20.499(1), b = 11.900(1), c = 4.589(1) Å, and V = 1119.4(3) ų. The strongest lines of the X-ray diffraction pattern are [(hkl), d-spacing in Å, (I)]: (331) 2.7480 (61), (141) 2.4788 (42), (711) 2.4197 (35), (441) 2.2455 (86), (801) 2.2408 (45), (442) 1.7124 (100), (802) 1.7074 (47), and (12.4.0) 1.4817 (51). The main bands in the FTIR spectrum of pertsevite-(OH) are 1354, 1261, 1178, 1022, 975, 929, 888, 745, 555 and OH-specific 3696, 3562, 3530 cm-1. [ABSTRACT FROM AUTHOR]