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@article{1174112,
author = {Plášil, Jakub and Fejfarová, Karla and Hloušek, Jan and Škoda, Radek and Novák, Milan and Sejkora, Jiří and Čejka, Jiří and Dušek, Michal and Veselovský, František and Ondruš, Petr and Majzlan, Juraj and Mrázek, Zdeněk},
article_location = {London},
article_number = {1},
doi = {http://dx.doi.org/10.1180/minmag.2013.077.1.12},
keywords = {štěpite; new mineral; uranium(IV) bis(hydrogenarsenate) tetrahydrate; crystal structure; chemical composition; oxidation zone; Jáchymov; Czech Republic},
language = {eng},
issn = {0026-461X},
journal = {Mineralogical Magazine},
title = {Štěpite, U(AsO3OH)(2) . 4H(2)O, from Jáchymov, Czech Republic: the first natural arsenate of tetravalent uranium},
volume = {77},
year = {2013}
}
TY - JOUR
ID - 1174112
AU - Plášil, Jakub - Fejfarová, Karla - Hloušek, Jan - Škoda, Radek - Novák, Milan - Sejkora, Jiří - Čejka, Jiří - Dušek, Michal - Veselovský, František - Ondruš, Petr - Majzlan, Juraj - Mrázek, Zdeněk
PY - 2013
TI - Štěpite, U(AsO3OH)(2) . 4H(2)O, from Jáchymov, Czech Republic: the first natural arsenate of tetravalent uranium
JF - Mineralogical Magazine
VL - 77
IS - 1
SP - 137-152
EP - 137-152
PB - Mineralogical Society
SN - 0026461X
KW - štěpite
KW - new mineral
KW - uranium(IV) bis(hydrogenarsenate) tetrahydrate
KW - crystal structure
KW - chemical composition
KW - oxidation zone
KW - Jáchymov
KW - Czech Republic
N2 - Stepite, tetragonal U(AsO3OH)(2)(H2O)(4) (IMA 2012-006), is the first natural arsenate of tetravalent uranium. It occurs in the Geschieber vein, Jachymov ore district, Western Bohemia, Czech Republic, as emerald-green crystalline crusts on altered arsenic. Associated minerals include arsenolite, behounekite, claudetite, gypsum, kaatialaite, the new mineral vysolcrite (IMA 2012-067) and a partially characterized phase with the formula (H3O)(2+)(UO2)(2)(AsO4)(2)center dot 6H(2)O. Stepite typically forms tabular crystals with prominent {001} and {010} faces, up to 0.6 mm in size. The crystals have a vitreous lustre and a grey to greenish grey streak. They are brittle with an uneven fracture and a very good cleavage on (001). Their Mobs hardness is about 2. Stepite is not fluorescent in either short-wave or long-wave ultraviolet light. It is biaxial (-) with refractive indices (at 590 nm) of alpha = 1.636(2), beta = 1.667(3), gamma = 1.672(2) and 2V(obs) < similar to 5 degrees, anomalous greyish to pale yellow interference colours, and no pleochroism. The composition is as follows: 0.12 Na2O, 50.19 UO2, 0.04 SiO4, 0.09 P2O5, 0.93 As2O5, 1.95 SO3, 16.41 H2O; total 107.90 wt.%, yielding an empirical formula (based on 12 0 a.p.f.u.) of (U1.01Na0.02)(Sigma 1.03)[(ASO(3)OH)(1.82)(PO3OH)(0.04)(SO4)(0.13)(SiO4)(0.01)](Sigma E2.00)center dot 4H(2)O. Stepite is tetragonal, crystallizing in space group I4(1)/acd, with a = 10.9894(1), c = 32.9109(6) angstrom, V = 3974.5(1) angstrom(3), Z = 16 and D-calc = 3.90 g cm(-3). The six strongest peaks in the X-ray powder-diffraction pattern [d(obs) in angstrom (I) (hkl)] are as follows: 8.190(100)(004), 7.008(43)(112), 5.475(18)(200), 4.111(16)(008), 3.395(20)(312,217), 2.1543(25)(419). The crystal structure of gtepite has been solved from single-crystal X-ray diffraction data by the charge-flipping method and refined to R-1 = 0.0353 based on 1434 unique observed reflections, and to wR(2) = 0.1488 for all 1523 unique reflections. The crystal structure of gtepite consists of sheets perpendicular to [001], made up of eight-coordinate uranium atoms and hydroxyarsenate 'tetrahedra'. The ligands surrounding the uranium atom consist of six oxygen atoms which belong to the hydroxyarsenate groups and two oxygen atoms which belong to interlayer H2O molecules. Each UO8 polyhedron is connected to five other U polyhedra via six AsO3OH groups. Adjacent electroneutral sheets, of composition [U4+(AsO3OH)(22)(-)](0), are linked by hydrogen bonds involving H2O molecules in the interlayers and OH groups in the sheets. The new mineral is named in honour of Josef Step (1863-1926), a Czech mining engineer and 'father' of the world's first radioactive spa at Jachymov.
ER -
PLÁŠIL, Jakub, Karla FEJFAROVÁ, Jan HLOUŠEK, Radek ŠKODA, Milan NOVÁK, Jiří SEJKORA, Jiří ČEJKA, Michal DUŠEK, František VESELOVSKÝ, Petr ONDRUŠ, Juraj MAJZLAN and Zdeněk MRÁZEK. Štěpite, U(AsO3OH)(2) . 4H(2)O, from Jáchymov, Czech Republic: the first natural arsenate of tetravalent uranium. \textit{Mineralogical Magazine}. London: Mineralogical Society, 2013, vol.~77, No~1, p.~137-152. ISSN~0026-461X. Available from: https://dx.doi.org/10.1180/minmag.2013.077.1.12.
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