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 ofšvenekite (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, As2O5 71.39, 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
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