Fluorapophyllite-(Cs), CsCa₄(Si₈O₂₀)F(H₂O)₈, a new apophyllite-group mineral from the Darai-Pioz Massif, Tien-Shan, Northern Tajikistan

Fluorapophyllite-(Cs) (IMA 2018-108a), ideally CsCa4(Si8O20)F(H2O)(8), is an apophyllite-group mineral from the moraine of the Darai-Pioz glacier, Tien-Shan, Northern Tajikistan. Associated minerals are quartz, pectolite, baratovite, aegirine, leucosphenite, pyrochlore, neptunite, fluorapophyllite-(K), and reedmergnerite. Fluorapophyllite-(Cs) is a hydrothermal mineral. It is colorless and has a vitreous luster and a white streak. Cleavage is perfect; it is brittle and has a stepped fracture. Mohs hardness is 4.5-5. D-meas. = 2.54(2) g/cm(3), D-calc. = 2.513 g/cm(3). Fluorapophyllite-(Cs) is unixial (+) with refractive indices (lambda = 589 nm) omega = 1.540(2), epsilon = 1.544(2). It is non-pleochroic. Chemical analysis by electron microprobe gave SiO2 48.78, Al2O3 0.05, CaO 22.69, Cs2O 10.71, K2O 1.13, Na2O 0.04, F 1.86, H2Ocalc. 14.61, -O=F2 -0.78, sum 99.09 wt.%; H2O was calculated from crystal-structure analysis. The empirical formula based on 29 (O + F) apfu, H2O = 8 pfu, is (Cs0.75K0.24)Sigma(0.99)(Ca3.99Na0.01)Sigma(4)(Si8.01Al0.01)Sigma 8.02O20.03F0.97(H2O)8, Z = 2. The simplified formula is (Cs,K)(Ca,Na)(4)(Si,Al) 8 O20F(H2O)(8). Fluorapophyllite-(Cs) is tetragonal, space group P4/mnc, a 9.060(6), c 15.741(11) angstrom, V 1292.10(19) angstrom(3). The crystal structure has been refined to R-1 = 4.31% based on 498 unique (F-o > 4 sigma F) reflections. In the crystal structure of fluorapophyllite-(Cs), there is one [4] T site occupied solely by Si,,T-O. = 1.615 angstrom. SiO4 tetrahedra link to form a (Si8O20)(8-)sheet perpendicular to [001]. Between the Si-O sheets, there are two cation sites: A and B. The A site is coordinated by eight H2O groups [O(4) site], A-O(4) = 3.152(4) angstrom; the A site contains Cs(0.75)K(0.24)A(0.01 square 0.01), ideally Cs apfu. The Cs-O bond length of 3.152 angstrom is definitely larger than the K-O bond length of 2.966-2.971 angstrom in fluorapophyllite-(K), KCa4(Si8O20)F(H2O)8. The [7]B site contains Ca3.99Na0.01, ideally Ca-4 apfu; < B-phi > = 2.417 angstrom (phi = O, F, H2O). The Si-O sheets connect via A and B polyhedra and hydrogen bonding; two H atoms have been included in the refinement. Fluorapophyllite-(Cs) is isostructural with fluorapophyllite-(K). Fluorapophyllite-(Cs) is a Cs-analogue of fluorapophyllite-(K)

Katerinopoulosite, (Nh4)2Zn(So4)2·6h2O, a new mineral from the Esperanza Mine, Lavrion, Greece

Katerinopoulosite, a new picromerite-group mineral, was discovered in the Esperanza mine, Lavrion District, Attikí Prefecture, Greece. The new mineral occurs in the oxidation zone of a sphalerite-rich orebody in association with chalcanthite, nickelboussingaultite, ammoniojarosite, aurichalcite, and goethite. Katerinopoulosite forms white, pale blue or pale green vermiform polycrystalline aggregates, in fact, anthodite crusts with separate anthodites up to 3-cm long and up to 5-mm thick. The lustre is vitreous, and the streak is white. Katerinopoulosite is brittle, has Mohs hardness of 2½ and an uneven fracture. Neither cleavage nor parting is observed. Dmeas = 1.97(2) g/cm3, Dcalc = 1.986 g/cm3. The new mineral is optically biaxial (+), with a = 1.492(2), b = 1.496(2), g = 1.502(2) (589 nm). 2V (meas.) = 80(5)°, 2V (calc.) = 79°. The infrared spectrum shows the presence of ammonium cations, sulfate anions, and water molecules. The chemical composition is (EDS-mode electron microprobe for Ni, Cu, and Zn; gas chromatography of ignition products for H, N and S, wt%): SO3 38.33, (NH4)2O 11.9, NiO 1.82, CuO 0.37, ZnO16.83, H2O 29.4, total 98.65. The empirical formula based on 2 S atoms per formula unit (apfu) is H0.13(NH4)1.91(Zn0.86Ni0.10Cu0.02)(SO4)2.00·6.75H2O. Katerinopoulosite is monoclinic, P21/a, a = 9.230(6), b = 12.476(4), c = 6.249(4)A, β = 106.79(5)°, V = 688.9(9)Ǻ3, and Z = 2. The strongest lines of the powder X-ray diffraction pattern [d, A (I, %) (hkl)] are: 5.400 (37) (011), 4.411 (19) (200), 4.314 (19) (021), 4.229 (24) (12–1), 4.161 (100) (20–1, 210, 111), 3.749 (53) (130), 3.034 (29) (211, 11–2). The new mineral is named in honour of the prominent Greek geologist and mineralogist Prof. Dr. Athanassios Katerinopoulos. The type material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia. © 2018 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart