科研之友
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摘要
Vysokyite, U4+[(AsO2(OH)(2)] 4(H2O)(4) (IMA 2012-067), was found growing on an altered surface of massive native As in the Geschieber vein, Jachymov ore district, Western Bohemia, Czech Republic. The new mineral was found in association with be. hounekite, stepite, kaatialaite, arsenolite, claudetite and gypsum. It forms extremely fibrous light-green crystals up to 8 mm long. Crystals have an alabaster lustre and a greenish-white to greyish streak. Vysokyite is brittle with uneven fracture and perfect cleavage along (100) and (001); the Mohs hardness is similar to 2. A density of 3.393 g/cm(3) was calculated using the empirical formula and unit-cell parameters obtained from a single-crystal diffraction experiment. Vysokyite is non-fluorescent under short or long wavelength UV radiation. It is colourless under the microscope, measured refractive indices are alpha%26apos; = 1.617(3), gamma%26apos; = 1.654(3); the estimated optical orientation is alpha%26apos; similar to X, gamma%26apos; similar to Z. The average of five spot wavelength dispersive spectroscopy (WDS) analyses is 29.44 UO2, 1.03 SiO2, 48.95 As2O5, 0.12 SO3,15.88 H2O (calc.), total 95.42 wt.%. The empirical formula of vysokyite (based on 20 O a.p.f.u.) is U-1.00[AsO2(OH)(2)](3.90)(SiO4)(0.16) (SO4)0.01 center dot 4H(2)O. The As-O-H and O-H vibrations dominate in the Raman spectrum. Vysoky%26apos; ite is triclinic, space group P (1) over bar, with a = 10.749(2), b = 5.044(3), c = 19.1778(7) angstrom, alpha = 89.872(15)degrees, beta = 121.534(15)degrees, gamma = 76.508(15)degrees, and V = 852.1(6) angstrom(3), Z = 2 and D-calc = 3.34 g.cm(-3). The strongest diffraction peaks in the X- ray powder diffraction pattern are [d(obs) in angstrom(I-rel.)(hkl)]: 8.872(100)(100), 8.067(50)(002), 6.399(7)(10 (3) over tilde), 4.773(6)(10 (4) over bar), 3.411(10)(30 (2) over bar), 3.197(18)(31 (3) over bar). The crystal structure of vysokyite was solved from single- crystal X- ray diffraction data by the charge- flipping method and refined to R-1 = 0.0595 based on 2718 unique observed reflection, and to wR(2) = 0.1160 for all 4173 unique reflections. The structure of vysokyite consists of UO8 square antiprisms sharing all of their vertices with 8 As-tetrahedra to form infinite chains parallel to [010]. These chains are linked by hydrogen bonds involving terminal (OH) groups of the double- protonated As- tetrahedra and molecules of H2O located between the chains. The new mineral is named in honour of Arnost Vysoky (1823 1872), the former chief of the Jachymov mines and smelters, chemist and metallurgist.
