Kampelite, Ba3Mg1.5Sc4(PO4)6(OH)3·4H2O, a new very complex Ba-Sc phosphate mineral from the Kovdor phoscorite-carbonatite complex (Kola Peninsula, Russia)

Kampelite, Ba3Mg1.5Sc4(PO4)6(OH)3·4H2O, is a new Ba-Sc phosphate from the Kovdor phoscorite-carbonatite complex (Kola Peninsula, Russia). It is orthorhombic, Pnma, a = 11.256(1), b = 8.512(1), c = 27.707(4) A, V = 2654.6(3) A3 and Z = 4 (from powder diffraction data) or a = 11.2261(9), b = 8.5039(6), c = 27.699(2) A, V = 2644.3(3) A3 (from single-crystal diffraction data). The mineral was found in a void within the calcite-magnetite phoscorite (enriched in hydroxylapatite and Sc-rich baddeleyite) inside the axial zone of the Kovdor phoscorite-carbonatite pipe. Kampelite forms radiated aggregates (up to 1.5 mm in diameter) of platy crystals grown on the surfaces of crystals of quintinite-2H in close association with pyrite, bobierrite and quintinite-3R. Kampelite is colourless, with a pearly lustre and a white streak. The cleavage is perfect on {001}, the fracture is smooth. Mohs hardness is about 1. In transmitted light, the mineral is colourless without pleochroism or dispersion. Kampelite is biaxial + (pseudouniaxial), α ≈ β = 1.607(2), γ = 1.612(2) (589 nm), and 2V calc = 0°. The calculated and measured densities are 3.28 and 3.07(3) g·cm−3, respectively. The mean chemical composition determined by electron microprobe is: MgO 4.79, Al2O3 0.45, P2O5 31.66, K2O 0.34, Sc2O3 16.17, Mn2O3 1.62, Fe2O3 1.38, SrO 3.44, and BaO 29.81 wt%. The H2O content estimated from the crystal-structure refinement is 7.12 wt%, giving a total of 96.51 wt%. The empirical formula calculated on the basis of P = 6 apfu (atoms per formula unit) is (Ba2.62Sr0.45K0.10Ca0.06)Σ3.23Mg1.60Mn0.28(Sc3.15Fe3+ 0.23Al0.12)Σ3.50(PO4)6(OH)2.61·4.01H2O. The simplified formula is Ba3Mg1.5Sc4(PO4)6(OH)3·4H2O. The mineral easily dissolves in 10% cold HCl. The strongest X-ray powder-diffraction lines [listed as d in A (I) (hkl)] are as follows: 15.80(100)(001), 13.86(45)(002), 3.184(18)(223), 3.129(19)(026), 2.756(16)(402), 2.688(24)(1010). The crystal structure of kampelite was refined to R 1 = 0.092 on the basis of 2620 unique observed reflections. It is based upon complex [MgBa2Sc4(PO4)6] layers consisting of the Ba-PO4 zigzag sheet inserted between two Mg-Sc-PO4 sheets. Raman spectrum of kampelite contains characteristic bands of vibrations of the PO4, ScO6 and H2O groups. Kampelite formed as a result of low-temperature hydrothermal alteration of Sc-bearing baddeleyite, which also produces Sc-rich pyrochlore and juonniite. The structural complexity parameters for kameplite are equal to 5.272 bits/atom and 1244.304 bits/cell, which points out that the mineral is structurally very complex, in agreement with its late-stage hydrothermal origin. The mineral is named in honour of Russian mining engineer Felix Borisovich Kampel’ (b. 1935) for his contribution to the development of technologies of mining and processing of complex magnetite-apatite-baddeleyite ores of the Kovdor deposit.