Nikolai N. Pertsev

Lakargiite CaZrO3: A new mineral of the perovskite group from the North Caucasus, Kabardino-Balkaria, Russia

Abstract Lakargiite CaZrO3-the zirconium analog of perovskite [Pbnm, a = 5.556(1), b = 5.715(1), c = 7.960(1) Å, V 252.7(1) Å3, Z = 4]-was discovered as an accessory mineral in high-temperature skarns in carbonate-silicate rocks occurring as xenoliths in ignimbrites of the Upper-Chegem (Verkhniy Chegem) volcanic structure, the North Caucasus, Kabardino-Balkaria, Russia. Lakargiite forms pseudo-cubic crystals up to 30-35 μm in size and aggregates up to 200 μm. Lakargiite is associated with spurrite, larnite, calcio-olivine, calcite, cuspidine, rondorfite, reinhardbraunsite, wadalite, perovskite, and minerals of the ellestadite group. The new perovskite mineral belongs to the ternary solid solution CaZrO3-CaTiO3-CaSnO3 with a maximum CaZrO3 content of ca. 93%, maximum CaTiO3 content of 22%, and maximum CaSnO3 content of 20%. Significant impurities are Sc, Cr, Fe, Ce, La, Hf, Nb, U, and Th. Raman spectra of lakargiite are similar to those of the synthetic phase Ca(Zr,Ti)O3 with strong bands at 352, 437, 446, 554, and 748 cm-1. Lakargiite crystallized under sanidinite-facies conditions of contact metamorphism characterized by very high temperatures and low pressures.

Chegemite Ca7(SiO4)3(OH)2 – a new humite-group calcium mineral from the Northern Caucasus, Kabardino-Balkaria, Russia

The new mineral chegemite Ca7(SiO4)3(OH)2 ( Pbnm , Z = 4)1, a = 5.0696(1), b = 11.3955(1), c = 23.5571(3) A; V = 1360.91(4) A3 – the calcium and hydroxyl analogue of humite – was discovered as a rock-forming mineral in high-temperature skarns in calcareous xenoliths in ignimbrites of the Upper Chegem volcanic structure, Northern Caucasus, Kabardino-Balkaria, Russia. The chegemite forms granular aggregates with grain sizes up to 5 mm and is associated with various high-temperature minerals: larnite, spurrite, rondorfite, reinhardbraunsite, wadalite, lakargiite, and srebrodolskite, corresponding to the sanidinite metamorphic facies. The empirical formula of the holotype chegemite (mean of 68 analyses) is Ca7(Si0.997Ti0.003O4)3(OH)1.48F0.52. Chegemite is characterized by the following optical properties: 2VZ = −80(8)°, α = 1.621(2), β = 1.626(3), γ = 1.630(2); Δ = 0.009; density D calc = 2.892 g/cm3. The crystal structure, including hydrogen positions, has been refined from single-crystal Mo K α X-ray diffraction data to R = 2.2 %. Octahedral Ca–O distances are similar to those of γ-Ca2SiO4 (calcio-olivine). As is characteristic of OH-dominant humite-group minerals, two disordered H positions could be resolved. The main bands in the FTIR-spectra of chegemite are at 3550, 3542, 3475, 927, 906, 865, 820, 800, 756, 705, 653, 561, 519 and 437 cm−1. Those in non-polarized Raman spectra are at 389, 403, 526, 818, 923.5, 3478, 3551 and 3563 cm−1. The X-ray diffraction powder-pattern (Fe K α-radiation) shows the strongest lines {d \[A\]( I obs)} at: 1.907(10), 2.993(8), 2.700(8), 3.015(7), 2.720(7), 2.834(6), 3.639(5), and 3.040(5).

Vorlanite (CaU6+O4) - A new mineral from the Upper Chegem caldera, Kabardino-Balkaria, Northern Caucasus, Russia

Abstract 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 in 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) Å3, and Z = 2. X-ray photoelectron spectroscopy indicate that all U in vorlanite is hexavalent. The mineral is isostructural with fluorite and uraninite (U4+O2). In contrast to synthetic rhombohedral 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.

Elbrusite-(Zr)—A new uranian garnet from the Upper Chegem caldera, Kabardino-Balkaria, Northern Caucasus, Russia

Abstract Elbrusite-(Zr) Ca3(U6+Zr)(Fe3+2 Fe2+)O12, a new uranian garnet (Ia3̅d, a ≈ 12.55 Å, V ≈ 1977 Å3, Z = 8), within the complex solid solution elbrusite-kimzeyite-toturite Ca3(U,Zr,Sn,Ti,Sb,Sc,Nb...)2(Fe,Al,Si,Ti)3O12 was discovered in spurrite zones in skarn xenoliths of the Upper Chegem caldera. The empirical formula of holotype elbrusite-(Zr) with 25.14 wt% UO3 is (Ca3.040Th0.018Y0.001)Σ3.059(U6+0.658Zr1.040Sn0.230Hf0.009Mg0.004)Σ1.941(Fe3+1.575Fe2+0.559Al0.539Ti40.199Si0.099Sn0.025V5+0.004)Σ3O12. Associated minerals are spurrite, rondorfite, wadalite, kimzeyite, perovskite, lakargiite, ellestadite-(OH), hillebrandite, afwillite, hydrocalumite, ettringite group minerals, and hydrogrossular. Elbrusite-(Zr) forms grains up to 10-15 μm in size with dominant {110} and minor {211} forms. It often occurs as zones and spots within Fe3+-dominant kimzeyite crystals up to 20-30 μm in size. The mineral is dark-brown to black with a brown streak. The density calculated on the basis of the empirical formula is 4.801 g/cm3 The following broad bands are observed in the Raman spectra of elbrusite-(Zr): 730, 478, 273, 222, and 135 cm-1. Elbrusite-(Zr) is radioactive and nearly completely metamict. The calculated cumulative dose (α-decay events/mg) of the studied garnets varies from 2.50 × 1014 [is equivalent to 0.04 displacement per atom (dpa)] for uranian kimzeyite (3.36 wt% UO3), up to 2.05 × 1015 (0.40 dpa) for elbrusite-(Zr) with 27.09 wt% UO3.

Toturite Ca3Sn2Fe2SiO12—A new mineral species of the garnet group

Abstract 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 (Ca2.989Fe2+0.011)Σ3(Sn4+1.463Sb5+0.325Ti4+0.193Zr0.013Mg0.003Nb5+0.002Cr0.001)Σ2(Fe3+1.633Al0.609Si0.552Ti4+0.166Fe2+0.039V5+0.001)Σ3O12. The mineral forms thin regular growth zones and irregular spots in the Fe3+-dominant analog of kimzeyite. Toturite is cubic, Ia3̅d, 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.

Bitikleite-(SnAl) and bitikleite-(ZrFe): New garnets from xenoliths of the Upper Chegem volcanic structure, Kabardino-Balkaria, Northern Caucasus, Russia

Abstract 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-tazheranitekimzeyite pseudomorphs after zircon. Bitikleite-(SnAl) has a = 12.5240(2) Å, V = 1964.40(3) Å3 and bitikleite-(ZrFe) has a = 12.49 Å, V = 1948.4 Å3 (Ia3d, 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

Kumtyubeite Ca5(SiO4)2F2—A new calcium mineral of the humite group from Northern Caucasus, Kabardino-Balkaria, Russia

Abstract Kumtyubeite, Ca5(SiO4)2F2-the fluorine analog of reinhardbraunsite with a chondrodite-type structure-is a rock-forming mineral found in skarn carbonate-xenoliths in ignimbrites of the Upper Chegem volcanic structure, Kabardino-Balkaria, Northern Caucasus, Russia. The new mineral occurs in spurrite-rondorfite-ellestadite zones of skarn. The empirical formula of kumtyubeite from the holotype sample is Ca5(Si1.99Ti0.01)Σ2O8(F1.39OH0.61)Σ2. Single-crystal X-ray data were collected for a grain of Ca5(SiO4)2(F1.3OH0.7) composition, and the structure refinement, including a partially occupied H position, converged to R = 1.56%: monoclinic, space group P21/a, Z = 2, a = 11.44637(18), b = 5.05135(8), c = 8.85234(13) Å, β = 108.8625(7)°, V = 484.352(13) Å3. For direct comparison, the structure of reinhardbraunsite Ca5(SiO4)2(OH1.3F0.7) from the same locality has also been refined to R = 1.9%, and both symmetry independent, partially occupied H sites were determined: space group P21/a, Z = 2, a = 11.4542(2), b = 5.06180(10), c = 8.89170(10) Å, β = 108.7698(9)°, V = 488.114(14) Å3. The following main absorption bands were observed in kumtyubeite FTIR spectra (cm-1): 427, 507, 530, 561, 638, 779, 865, 934, 1113, and 3551. Raman spectra are characterized by the following strong bands (cm-1) at: 281, 323, 397 (ν2), 547 (ν4), 822 (ν1), 849 (ν1), 901 (ν3), 925 (ν3), 3553 (VOH). Kumtyubeite with compositions between Ca5(SiO4)2F2 and Ca5(SiO4)2(OH1.0F1.0) has only the hydrogen bond O5-H1···F5′, whereas reinhardbraunsite with compositions between Ca5(SiO4)2(OH1.0F1.0) and Ca5(SiO4)2(OH)2 has the following hydrogen bonds: O5-H1···F5′, O5-H1···O5′, and O5-H2···O2.

Fukalite: An example of an OD structure with two-dimensional disorder

Abstract The real crystal structure of fukalite, Ca4Si2O6(OH)2(CO3), was solved by means of the application of order-disorder (OD) theory and was refined through synchrotron radiation diffraction data from a single crystal. The examined sample came from the Gumeshevsk skarn copper porphyry deposit in the Central Urals, Russia. The selected crystal displays diffraction patterns characterized by strong reflections, which pointed to an orthorhombic sub-structure (the “family structure” in the OD terminology), and additional weaker reflections that correspond to a monoclinic real structure. The refined cell parameters are a = 7.573(3), b = 23.364(5), c = 11.544(4) Å, β = 109.15(1)°, space group P21/c. This unit cell corresponds to one of the six possible maximum degree of order (MDO) polytypes, as obtained by applying the OD procedure. The derivation of the six MDO polytypes is presented in the Appendix1. The intensity data were collected at the Elettra synchrotron facility (Trieste, Italy); the structure refinement converged to R = 0.0342 for 1848 reflections with I > 2σ(I) and 0.0352 for all 1958 data. The structure of fukalite may be described as formed by distinct structural modules: a calcium polyhedral framework, formed by tobermorite-type polyhedral layers alternating along b with tilleyitetype zigzag polyhedral layers; silicate chains with repeat every fifth tetrahedron, running along a and linked to the calcium polyhedral layers on opposite sides; and finally rows of CO3 groups parallel to (100) and stacked along a.

Rusinovite, Ca10(Si2O7)3Cl2: a new skarn mineral from the Upper Chegem caldera, Kabardino-Balkaria, Northern Caucasus, Russia

Rusinovite, Ca 10 (Si 2 O 7 ) 3 Cl 2 , was discovered in an altered carbonate-silicate xenolith enclosed in ignimbrites of the Upper Chegem volcanic caldera. The mineral is named after Vladimir Leonidovich Rusinov (1935–2007), a Russian petrologist and expert in the field of thermodynamics of non-equilibrium mineral systems. A synthetic analogue of rusinovite is also known. The new mineral has an OD structure of which only the average structure could be determined based on strong and sharp reflections recorded by single-crystal X-ray diffraction: space group Cmcm , a = 3.7617(2), b = 16.9385(8), c = 17.3196(9) A, V = 1103.56(10) A 3 , Z = 2. The average structure ( R 1 = 3.18 %) is characterized by columns of face-sharing disilicate units extending parallel to a . However, in the true structure only each second (Si 2 O 7 ) unit is occupied. Although rusinovite has a stoichiometry similar to the apatite-group mineral nasonite, Pb 6 Ca 4 (Si 2 O 7 ) 3 Cl 2 , the two structures are considerably different. Rusinovite has following optical properties: α = 1.645(2), β = 1.664(2), γ = 1.675(3); Δ = 0.030, 2V meas = −75(10) °; 2V calc = −74.6 °; the Mohs hardness is 4–5, the density is 2.91 g/cm 3 . The mineral forms fibrous crystals often intergrown into spherolites and displays good cleavage parallel to (010). The Raman spectrum of rusinovite strongly resembles that of another skarn calcium-disilicate: rankinite, Ca 3 Si 2 O 7 .

Pavlovskyite Ca8(SiO4)2(Si3O10): A new mineral of altered silicate-carbonate xenoliths from the two Russian type localities, Birkhin massif, Baikal Lake area and Upper Chegem caldera, North Caucasus

Abstract 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) Å3, 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) Å3, 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.