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Švenekite, Ca[AsO2(OH)2]2, a new mineral from Jáchymov, Czech Republic

Published online by Cambridge University Press:  05 July 2018

P. Ondruš ,
R. Skála ,
J. Plášil ,
J. Sejkora ,
F. Veselovský ,
J. Čejka ,
A. Kallistová ,
J. Hloušek ,
K. Fejfarová  and
R. Škoda
...Show all authors
P. Ondruš
Affiliation:
Biskupský dvůr 2, Prague 1, 110 00, Czech Republic
R. Skála
Affiliation:
Institute of Geology ASCR, v.v.i., Rozvojová 269, Prague 6, 165 00, Czech Republic
J. Plášil*
Affiliation:
Institute of Physics ASCR, v.v.i., Na Slovance 2, Prague 8, 182 21, Czech Republic
J. Sejkora
Affiliation:
Department of Mineralogy and Petrology, National Museum, Cirkusová 170, 193 00, Prague 9, Czech Republic
F. Veselovský
Affiliation:
Czech Geological Survey, Klárov 3, 118 21, Prague 1, Czech Republic
J. Čejka
Affiliation:
Department of Mineralogy and Petrology, National Museum, Cirkusová 170, 193 00, Prague 9, Czech Republic
A. Kallistová
Affiliation:
Institute of Geology ASCR, v.v.i., Rozvojová 269, Prague 6, 165 00, Czech Republic
J. Hloušek
Affiliation:
U Roháčových kasáren 24, 100 00, Prague 10, Czech Republic
K. Fejfarová
Affiliation:
Institute of Physics ASCR, v.v.i., Na Slovance 2, Prague 8, 182 21, Czech Republic
R. Škoda
Affiliation:
Department of Geological Sciences, Masaryk University, Kotlářská 2, Brno, 611 37, Czech Republic
M. Dušek
Affiliation:
Institute of Physics ASCR, v.v.i., Na Slovance 2, Prague 8, 182 21, Czech Republic
A. Gabašová
Affiliation:
Czech Geological Survey, Klárov 3, 118 21, Prague 1, Czech Republic
V. Machovič
Affiliation:
Institute of Chemical Technology, Prague, Technická 5, 16628, Prague 6, Czech Republic Institute of Rock Structures and Mechanics ASCR, v.v.i., V Holešovičkách 41, 18209, Prague 8, Czech Republic
L. Lapčák
Affiliation:
Institute of Chemical Technology, Prague, Technická 5, 16628, Prague 6, Czech Republic
*
* E-mail: plasil@fzu.cz
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Abstract

Švenekite (IMA 99-007), Ca[AsO2(OH)2]2, is a rare supergene arsenate mineral occurring in the Geschieber vein, Jáchymov ore district, Western Bohemia, Czech Republic. It grows directly on the granite rocks and occurs isolated from other arsenate minerals otherwise common in Jáchymov. Švenekite usually forms clear transparent coatings composed of indistinct radiating to rosette-shaped aggregates up to 3 mm across. They are composed of thin lens- or bladed-shaped crystals, usually 100 – 150 μm long. Švenekite is transparent to translucent and has a white streak and a vitreous lustre; it does not fluoresce under ultraviolet light. Cleavage is very good on {010}. The Mohs hardness is ∼2. Švenekite is biaxial, non-pleochroic. The refractive indices are α' = 1.602(2), γ' = 1.658(2). The empirical formula of švenekite (based on As + P + S = 2 a.p.f.u., an average of 10 spot analyses) is (Ca1.00Mg0.01)Σ1.01[AsO2(OH)2]1.96[PO2(OH)2]0.03(SO4)0.01. The simplified formula is Ca[AsO2(OH)2]2 and requires CaO 17.42, As2O571.39, H2O 11.19, total 100.00 wt.%. Raman and infrared spectroscopy exhibit dominance of O – H vibrations and vibration modes of distorted tetrahedral AsO2(OH)2 units. Švenekite is triclinic, space group P, with a = 8.5606(5), b = 7.6926(6), c = 5.7206(4) Å, α = 92.605(6), β = 109.9002(6), γ = 109.9017(6)º, and V = 327.48(4) Å3, Z = 2, Dcalc = 3.26 g·cm–3. The a:b:c ratio is 0.7436:1:1.1082 (for single-crystal data). The six strongest diffraction peaks in the X-ray powder diffraction pattern are [d (Å)/I(%)/(hkl)]: 3.968(33)(20); 3.766(35)(2); 3.697(49)(101); 3.554(100)(020); 3.259(33)(20); 3.097(49)(11). The crystal structure of švenekite was refined from single-crystal X-ray diffraction data to R1 = 0.0250 based on 1309 unique observed, and to wR2 = 0.0588, for all 1588 unique reflections (with GOFall = 1.20). The structure of švenekite consists of sheets of corner-sharing CaO8 polyhedra and AsO2 OH2 groups, stacked parallel to (001). Adjacent sheets are linked by hydrogen bonds. The švenekite structure possesses very short symmetrical hydrogen bonds (with the D–H lengths ∼1.22 Å). The mineral is named to honour Jaroslav Švenek, the former curator of the mineralogical collection of the National Museum in Prague, Czech Republic.

Keywords

švenekitenew mineralcalcium bis (dihydrogen-arsenate)crystal structureJáchymov
Type
Research Article
Information
Mineralogical Magazine , Volume 77 , Issue 6 , August 2013 , pp. 2711 - 2724
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2013

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Footnotes

†

Deceased June 22, 2006

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