Uranosphaerite from Horni Halze near Medenec (Krusne hory Mountains, Czech Republic): description and vibrational characteristics

Sejkora, Jiří

doi:10.1127/0077-7757/2008/0116

Cited by 5 publications

(1 citation statement)

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“…Observed lowering of symmetry of the structural units causes corresponding Raman activation of some or all vibrations and splitting of doubly-or triply-degenerate ones. The Raman spectrum was interpreted with reference to Nakamoto (1986), Čejka (1999), Sejkora et al (2002Sejkora et al ( , 2004Sejkora et al ( , 2008, Ardelean et al (2006) and Frost et al (2011) and references therein.…”

Section: Raman Spectroscopymentioning

confidence: 99%

Horákite, a new hydrated bismuth uranyl-arsenate-phosphate mineral from Jáchymov (Czech Republic) with a unique uranyl-anion topology

Plášil¹,

Kampf²,

Sejkora³

et al. 2018

Jour. Geosci.

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Horákite, ideally (Bi 7 O 7 OH)[(UO 2) 4 (PO 4) 2 (AsO 4) 2 (OH) 2 ]•3.5H 2 O, is a new uranyl mineral discovered on a specimen originating from Jáchymov, Czech Republic (most probably from the Geister vein, Rovnost mine). It occurs as a supergene alteration mineral in association with phosphuranylite (overgrowing older metatorbernite-metazeunerite) in a quartz gangue with abundant tennantite. Horákite forms greenish-yellow to pale yellow prismatic crystals clustering to acicular aggregates, up to 1 mm across. Crystals are transparent to translucent with a vitreous luster. The mineral has a light yellow streak. Estimated Mohs' hardness is ~2. The cleavage is perfect on {100}. The calculated density is 6.358 g/cm 3. Horákite is optically biaxial (+), α ≈ 1.81, β ≈ 1.84, γ ≈ 1.88 (measured in white light); 2V obs. is 78(1)°, 2V calc. is 83°; non-pleochroic. The optical orientation is X = b, Z ≈ c. Electron-microprobe analysis yielded the empirical formula (Bi 7.01 Pb 0.14)O 7 OH[(U 1.01 O 2) 4 (P 1.03 O 4) 2 (As 0.74 Si 0.23 O 4) 2 (OH) 2 ]•3.5H 2 O based on 37.5 O apfu. Horákite is monoclinic, C2/c, a = 21.374(2), b = 15.451(3), c = 12.168(2) Å, β = 122.26(1)° and V = 3398.1(10) Å 3 , Z = 4. The eight strongest X-ray powder-diffraction lines are [d obs Å(I)(hkl)]: 11.77(100)(110), 6.21(23)(-202), 5.55(23)(310,-112), 4.19(27)(-331), 3.54(61)(510,-423), 3.29(20)(331), 3.14(58)(241, 023) and 3.02(98)(150, 113,-533, mult.). The crystal structure refinement of horákite, refined to R = 5.95 % for 1774 unique observed reflections, revealed a novel sheet structure. It consists of topologically unique [(UO 2) 4 (PO 4) 2 (AsO 4) 2 (OH) 2 ] sheets (i.e., horákite topology), and an interstitial {(Bi 7 O 7 OH) (H 2 O) 3.5 } complex. Sheets result from the polymerization of UO 7 bipyramids by sharing edges to form tetrameric units; tetrahedrally coordinated sites are linked to the UO 7 both monodentately (T1 to U1) and bidentately (T2 to U2). The mineral is named after František Horák (1882-1919), the mining engineer in Jáchymov, and his grandson, Vladimír Horák (born 1964), an amateur mineralogist and expert on the mining history of the Jáchymov ore district.

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