ЦИНКЛИПСКОМБИТ, ZNFE23+ (РО4)2(ОН)2 - НОВЫЙ МИНЕРАЛ

Abstract

A new mineral zinclipscombitc has been found together with apophyllite, quartz, baryte, jarosite, plumboja-rositc, turquoise and calcite in the Silver Coin mine, Valmy, Edna Mountains, Humboldt Co., Nevada, USA. The new mineral forms spheroidal, fibrous aggregates; thickness of the fibers stretched along с is up to 20 urn; diameter of spherules - up to 2.5 mm. Color dark-green to brown, streak light-green to beige, luster vitreous, translucent. Mohs' hardness is 5, brittle, cleavage none observed, fracture uneven. Dmeas = 3.65(4) g/cm3 (by hydrostatic weighing), Ocaic= 3.727 g/cm3 (with the powder data). Wavcnumbers of absorption bands in the IR spectrum of zinclipscombitc are (cm-1; sh - shoulder, w - weak band; wavenumbers of the strongest bands are underlined): 3535, 3330 sh, 3260, 1625 w, 1530 w, 1068, 1047, 1022, 970 sh, 768 w, 684 w, 609, 502, 460. The Mossbauer spectrum of zinclipscombite contains only a doublet, corresponding to Fe3+ with 6-fold coordination, with quadrupolc splitting of 0.562 mm/s; Fe2+ is absent. The mineral is optically uniaxial, positive, ш = 1755(5), e= 1.795(5). Pleochroism: X= bright-green to blue-green, Z = light greenish brown (X> Z). Chemical composition (electron microprobc, mean of 5 point analyses, wt. %): CaO 0.30, ZnO 15.90, A1203 4.77, Fe203 35.14, P205 33.86, As2Os 4.05, H20 (determined by Penficld method) 4.94, total 98.96 %. The empirical formula, based on (P04,As04)2, is: (Zn076Ca002)2;o.78(Fe31+72Alo.36b.o8[(P04)1.86(As04)0.|4]5:200(OH),80-0.17H2O.The idealized formula is ZnFe2+(P04)2(OH)2. Zinclipscombitc is tetragonal, space group Р4Ъ2\2 or P4{2{2; a = = 7.242(2) А, с = 13.125(5) A, V= 688.4(5) A3, Z= 4. The strongest reflections of the powder diffraction pattern [d,k (/,%) (M0] are: 4.79(80)(111), 3.32(100)(113), 3.21(60)(210), 2.602(45)(213), 2.299(40)(214), 2.049(40)(106), 1.663(45)(226), 1.605(50)(421, 108). Zinclipscombite is an analogue of lipscombite, Fe2+Fe2+(P04)2(OH)2 (tetragonal), with Zn instead of Fe2+. The mineral is named for its chemical composition, the Zn-dominant analogue of lipscombite. The holotype specimen is deposited in the Mineralogical Collection of the Tcchnische Universitat Bergakademie Freiberg, Germany.