Paraershovite, Na3K3Fe3+2 (Si4O10OH)2(OH)2(H2O)4, a new mineral species from the Khibina alkaline massif, Kola peninsula, Russia: mineral description and crystal structure

• Published in: The Canadian Mineralogist
• Main Authors: Khomyakov AP, Sokolova E, Abdu Y, Hawthorne FC, CAMARA ARTIGAS, Fernando
• Other Authors: Cámara F
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2010
• Subjects: paraershovite; new mineral specie; crystal structure; Fe3+ silicate; ershovite; electron-microprobe analysi; Khibina; Kola Peninsula; Russia; kola peninsula
• Online Access: http://hdl.handle.net/2318/79071; https://doi.org/10.3749/canmin.48.2.279; http://www.canmin.org/content/48/2/279.abstract

Paraershovite, Na3K3Fe3+2 (Si4O10OH)2(OH)2(H2O)4, is a new silicate mineral species discovered in a hyperagpaitic pegmatite from Mount Yukspor, Khibina alkaline massif, Kola Peninsula, Russia. The mineral occurs as equant (100) platy and [001] elongate prismatic crystals up to 0.5–1 mm and aggregates up to 2–3 mm sporadically scattered in a pegmatite matrix. Associated minerals are sodalite, aegirine, arfvedsonite, pectolite, shcherbakovite, lamprophyllite, lomonosovite, shafranovskite, villiaumite and natrophosphate. Crystals of paraershovite are yellow with orange or pinkish shades, with a white streak and vitreous luster. The mineral is translucent or transparent, and non-fluorescent under 240–400 nm ultraviolet radiation. Paraershovite has a perfect {100} cleavage. It is brittle, has a step-like and splintery fracture, and a Mohs hardness of 3. Its observed and calculated densities (g/cm3) are 2.60(3) (by microvolumetric methods) and 2.584 (using the empirical formula), respectively. It is biaxial positive, with α 1.569(2), β 1.583(2), γ 1.602(2), 2V(meas.) = 80(3)°, 2V(calc.) = 82°, non-pleochroic, dispersion r > v (weak), with X ∧ c = 84°, Y ∧ c = 66°, Z ∧ c = 24°. Paraershovite is triclinic, space group P1̅, a 10.1978(5), b 12.0155(6), c 5.2263(3) Å, α 103.439(1), β 96.020(1), γ 91.683(1)°, V 618.46(3) Å3, Z = 1. The strongest lines in the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 11.778(100)(010), 4.390(70)(11̅1, 02̅1), 3.012(70)(230, 3̅20), 2.606(70)(32̅1, 131, 01̅2, 1̅1̅2), 4.109(60)(1̅11, 1̅2̅1) and 2.730(60)(3̅2̅1, 1̅4̅1, 14̅1, 31̅1, 221). A chemical analysis with an electron microprobe gave Na2O 7.77, MgO 0.24, SiO2 49.67, Al2O3 0.58, K2O 14.07, Fe2O3 11.29, MnO 0.73, TiO2 3.32, F 0.39, H2O 10.98, O = F –0.16, sum 98.88 wt.%; the valence state of Fe was determined by Mössbauer spectroscopy, and the amount of H2O was calculated from the crystal-structure refinement. The empirical formula based on 28 anions is (Na2.44□1.56)∑4K2.91 (Fe3+1.38Ti0.40Al0.11Mn2+0.10 Mg0.06)∑2.05Si8.05O20 ...