| Description |
Dobšináite, ideally Ca2Ca(AsO4)2·2H2O, is a new supergene mineral from the Dobšiná deposit, Slovak Republic, associated with phaunouxite, picropharmacolite, erythrite-hörnesite, gypsum and aragonite. It forms white to pink clusters or polycrystalline aggregates up to 1–4 mm in size consisting of densely intergrown, slightly rounded thin tabular to platy crystals up to 0.1 mm in size. Dobšináite has a white streak, vitreous luster, does not fluoresce under either short- or long-wave ultraviolet light. Cleavage on {010} is good, the Mohs hardness is ~3, and dobšináite is brittle with an uneven fracture. The calculated density is 3.395 g/cm3. Dobšináite is optically biaxial negative, the indices of refraction are ?´ = 1.601(2) and ?´ = 1.629(2) and 2Vmeas. is 60° (+/– 20°). Dobšináite is monoclinic, space group P21 /c, a = 5.990(2), b = 13.013(4), c = 5.726(2) A, ß = 108.47(3)°, V = 423.3(3) A3, Z = 2. The seven strongest lines in the X-ray powder diffraction pattern are as follows: d (A)/I(hkl): 5.197/37(110); 3.443/38(130); 3.385/66(031); 3.249/77(040); 3.201/42(13–1); 3.026/100(121) and 2.822/60(10–2). The chemical analyses by electron microprobe yielded (in wt. %) CaO 36.74, MgO 0.89, NiO 0.37, CoO 0.51, P2O5 0.03, As2O5 52.75, SO3 0.18, H2Ocalc. 8.31, total 99.78. The resulting empirical formula on the basis of 10 O atoms per formula unit is Ca2(Ca0.84Mg0.10Co0.03Ni0.02)?0.99[(AsO4)1.99(SO4)0.01]?2.00·2H2O. Dobšináite is the Ca-dominant member of the roselite group as confirmed by stoichiometry, X-ray powder diffraction data and Raman spectroscopy. It is named after its type locality Dobšiná, Slovak Republic. Dobšináite was formed during weathering of primary Co and As-bearing ore minerals (safflorite, arsenopyrite) in a Ca enriched environment under relatively dry conditions.
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