Vanadio-pargasiteNaCa2Mg4V[Si6Al2]O22(OH)2– new mineral of the amphibole group

Reznitsky L. Z., Sklyarov E. V., Cametti G., Armbruster T., Suvorova L. F., UshchapovskayaZ. F.,Barash I. G.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2017. V. 146. N 6. P. 62-74

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Language: Russian

Abstract

This new mineral was discovered in the Pereval marble quarry in Cr-V-bearing marbles, in the Sludyanka district (South Baikal region, Russia). It was named vanadio-pargasite as vanadium-bearing analogue of pargasite, according to classification of the amphibole supergroup and CNMNC recommendations. Associated minerals are black Cr-V-spinel (magnesiocoulsonite-magnesiochromite) and red Cr-V-bearing spinel, calcite, dolomite, Cr-V-bearing diopside and chlorite, phlogopite and forsterite. Vanadio-pargasite forms subhedral long- and short-prismatic crystals sized 0.10—0.8  0.05—0.10 mm, with faces (110), (010), and perfect cleavage by (110). Color is (macroscopic) bright-green to emerald-green with vitreous luster, in thin sections and powder — pale- green, without pleochroism. Biaxial, positive, 2V = 86° ± 2°, Ng = 1.659(2), Nm = 1.651(2), Np = 1.643(2). Hardness (Mohs) ~ 6, (VHN50;100) = mean 795; range 752—824 kg/mm2. Density dmeas = 3.05(5) g/cm3, dcalc = 3.112 g/cm3. On thermogram in the interval 654-1081 °C H2O is given off with endothermic effect. In the range 900—1183 °C the main endothermic effect is water release, possibly also F and melting of the mineral (1020 °C). IRS absorption bands (cm–1) — 3445, 1633, 980, 469. Monoclinic, sp. gr. 2C/m, unit cell parameters: a = 9.914(3), b = 18.003(2), c = 5.300(2) Å, β = 105.69(3)°, V = 910.7(5) Å3, Z = 2. Strongest lines of diffraction pattern [d, Å (I) (hkl)]: 8.98 (15) (020); 8.43 (40) (110); 3.27 (30) (240); 3.14 (100) (310); 2.82 (35) (330); 2.70 (18) (151), 2.34 (15) (42-1); 1.898 (15) (510); 1.445 (25) (4.10-1). Mean chemical composition (microprobe, 528 an.) wt % — SiO2 42.75, TiO2 0.14, Al2O3 12.75, Cr2O3 0.44, V2O3 5.92, MgO 19.15, FeO 0.03, MnO 0.01, CaO 12.52, Na2O 3.45, K2O 0.41, F (wet chem.) 0.74, H2O (calc.) 1.75, total 99.91. Simplified formula is: K0.1Na0.9Ca2.0Mg4.0V0.7Al0.3(Si6.1Al1.9)8.0O22(OH1.7F0.3)2.0. Holotype material is deposited in the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia (catalogue numbers 5035/1, 5035/2 and 5035/3).

Key words: new mineral, amphibole, vahadio-pargasite, South Baikal region, Russia.