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

Abstract

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.

Exploring the Role of Organic Functional Groups in the Ionothermal Synthesis of Uranyl Phosphate Materials

“…Upon heating autunite‐type compounds above 130 °C, the autunite sheet reorganizes to the uranophane topology, again highlighting the tendency of uranyl phosphates to adopt one of these four main structural unit types [34] . There are very few examples where inorganic uranyl phosphate structures deviate significantly from the four main types [35,36] …”

“…[34] There are very few examples where inorganic uranyl phosphate structures deviate significantly from the four main types. [35,36] Introduction of organic functional groups to form tri-, di-, and monoalkyl phosphates impacts the coordinating ability of the phosphate anion and influences the overall crystal chemistry of resulting compounds. Most relevant to nuclear fuel reprocessing and PUREX are tributyl phosphate and the radiolytic degradation contaminants di-and monobutyl phosphate.…”

Hydrogen bonding in the crystal structure of phurcalite, Ca2[(UO2)3O2(PO4)2]·7H2O: single-crystal X-ray study and TORQUE calculations

“…This makes uranyl phosphate and arsenate minerals essential for controlling U mobility in the environment. Nowadays, more than 50 uranyl phosphates and arsenates are known to occur in nature, some of them being discovered in the past decade (Mills et al, 2008;Plá šil et al, 2010Plá šil et al, , 2018Pekov et al, 2012).…”

Namibit a doprovodná mineralizace fluoritové žíly Nadějná u Kotliny v Krušných horách (Česká republika)

“…U získaných spekter byly aplikovány korekce na fluorescenci. Interpretace Ramanových spekter byla provedena s přihlédnutím k publikacím Chukanov, Vigasina (2020); Grice (2002);Selvamani et al (2016);Frost et al (2006 Frost et al ( , 2010Frost et al ( , 2011Kolitsch, Giester (2000);Plášil et al (2018); Hardcastle, Wachs (1992);Taylor et al (1984); Jones, Jackson (1993) a k pracím dalších autorů v nich citovaných.…”