Original paper

Okruschite, Ca2Mn2+

Chukanov, Nikita V.; Möhn, Gerhard; Pekov, Igor V.; Belakovskiy, Dmitriy I.; Bychkova, Yana V.; Gurzhiy, Vladislav V.; Lorenz, Joachim A.

Abstract

The new mineral okruschite (IMA No. 2013–097), the arsenate analogue of roscherite, was discovered in a hydrothermal vein cross-cutting rhyolite exposed in the Fuchs quarry, near Sailauf, Spessart Mountains, Bavaria, Germany. Associated minerals are braunite, Mn-bearing calcite and arseniosiderite. Okruschite forms tabular aggregates up to 0.15 × 0.3 × 0.3 mm in size of curved and somewhat misaligned laths. It is white, semitransparent; lustre is vitreous. Dmeas = 3.33(2), Dcalc = 3.340 g/cm3. Okruschite is optically biaxial (–), α = 1.671(3), β = 1.682(2), γ = 1.687(3), 2V meas = 65(5)°. The infrared spectrum is given. The chemical composition is (electron microprobe, B and Li by ICP MS, H2O by gas chromatography of ignition products, wt. %): Li2O 0.04, BeO 7.70, MgO 1.68, CaO 8.28, MnO 16.27, FeO 4.89, Al2O3 0.22, As2O5 51.11, H2O 11.0, total 101.19. The empirical formula based on 34 O atoms is: Ca1.99(Mn3.09Fe0.92Mg0.56Al0.06Li0.04)Σ4.67Be4.15(AsO4)5.99(OH)3.64 · 6.40H2O. The simplified formula is Ca2Mn2+ 5Be4(AsO4)6(OH)4 · 6H2O. Okruschite is monoclinic, C2/c, a = 16.33(4), b = 12.03(3), c = 6.93(1) Å, β = 94.84(5)°, V = 1357(4) Å3, Z = 2. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 9.68 (39) (110), 4.95 (34) (310), 4.17 (34) (–311), 3.25 (100) (–202, 330), 3.11 (32) (–421), 2.841 (27) (240), 2.711 (26) (600), 1.726 (26) (461, –552, 004). Okruschite is named after Professor Martin Okrusch, from Germany. Type material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow.

Keywords

beryllium arsenatefuchs quarrynew mineralokruschiterhyoliteroscherite groupsailaufspessart