none 10.1180/minmag.2013.077.6.02 Mineralogical Society The Mineralogical Society 7149 63849851 5840 2021020408423921245 10.1180 2021-02-04T09:19:32Z 2013-08-22T19:39:47Z 6 Mineralogical Magazine Mineral. mag. 0026-461X 1471-8022 08 2013 77 6 P. Ondruš R. Skála J. Plášil J. Sejkora F. Veselovský J. Čejka A. Kallistová J. Hloušek K. Fejfarová R. Škoda M. Dušek A. Gabašová V. Machovič L. Lapčák Abstract Švenekite (IMA 99-007), Ca[AsO 2 (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 (Ca 1.00 Mg 0.01 ) Σ1.01 [AsO 2 (OH) 2 ] 1.96 [PO 2 (OH) 2 ] 0.03 (SO 4 ) 0.01. The simplified formula is Ca[AsO 2 (OH) 2 ] 2 and requires CaO 17.42, As 2 O 5 71.39, H 2 O 11.19, total 100.00 wt.%. Raman and infrared spectroscopy exhibit dominance of O – H vibrations and vibration modes of distorted tetrahedral AsO 2 (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) Å 3 , Z = 2, D calc = 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)(2 0); 3.766(35)(2 ); 3.697(49)(101); 3.554(100)(020); 3.259(33)(2 0); 3.097(49)(1 1). The crystal structure of švenekite was refined from single-crystal X-ray diffraction data to R 1 = 0.0250 based on 1309 unique observed, and to wR 2 = 0.0588, for all 1588 unique reflections (with GOF all = 1.20). The structure of švenekite consists of sheets of corner-sharing CaO 8 polyhedra and AsO 2 OH 2 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. 07 05 2018 08 2013 2711 2724 S0026461X00005211 https://www.cambridge.org/core/terms 10.1180/minmag.2013.077.6.02 https://www.cambridge.org/core/product/identifier/S0026461X00005211/type/journal_article https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0026461X00005211 http://www.ingentaconnect.com/content/minsoc/mag/2013/00000077/00000006/art00002 http://minmag.geoscienceworld.org/cgi/doi/10.1180/minmag.2013.077.6.02 10.1107/S0567739473000689 Microbeam Analysis 104 1985 Pouchou Journal of the Czech Geological Society Supplement to secondary and rock-forming minerals of the Jáchymov ore district 48 149 2003a Ondruš 10.1107/S0567740881006043 Keller, P. (1971) Die Kristallchemie der Phosphat- und Arsenatminerale unter besonderer Berücksichtung der Kationen-Koordinationspolyeder und des Kristallwassers, Teil A. 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