Schafarzikite from the type locality Pernek (Male Karpaty Mountains, Slovak Republic) revisited

A rare mineral schafarzikite, an oxide of Fe2+ and Sb3+, was found after more than 80 years at the type locality near Pernek (Male Karpaty Mountains, Slovak Republic). Crystals, druses, and crusts of schafarzikite occur on fractures in quartz-carbonate-stibnite hydrothermal ores. The Sb mineralization is bound to black shales and phyllites in a zone of actinolitic rocks. Associated minerals include ankerite, berthierite, stibnite, valentinite, kermesite, senarmontite, and gypsum. Prismatic crystals of schafarzikite are 0.1-1.0 mm, rarely up to 1.5 mm large, with the dominant forms {110}, {121}, {112}, {010}, {221}, {131}, and {231}. The optical properties are: uniaxial, with relatively strong pleochroism in red-brown tints; refraction indices higher than 1.74; the average refraction index, calculated from the Gladstone-Dale equation, is 2.001. The physical properties of schafarzikite from Pernek are: dark brown to black color, adamantine to metallic luster, brown streak; translucent (brown to orange) in very thin fragments; good 11001 cleavage and perfect cleavage along unindexed planes parallel to z axis, tenacity-brittle; VHN10g, microhardness = 251 and 278 kp/mm(2) (for two cuts with differing orientation), corresponding to Mohs' hardness of 3.5-4; calculated density D-x = 5.507 g/cm(3). The electron microprobe analysis gave FeO 19.38, ZnO 0.02, PbO 0.02, Sb2O3 80.36, As2O3 0.55, Bi2O3 0.16, SO2 0.04, and calculated formula Fe-0.97(Sb1.99As0.02)Sigma O-2.01(4). The XRD pattern was indexed in a tetragonal setting, with refined unit-cell parameters are a = 8.6073(2), c = 5.9093(3) angstrom, V = 437.80(2) angstrom(3), C : a = 0.6865. Thermogravimetric (TG) curve shows mass gain of 1.62 wt. % in the range 20-580 degrees C, and 5.28 wt. % in the range 580-850 degrees C caused by Fe2+ and Sb3+ oxidation, respectively. The product of TG analysis is a phase isostructural with rutile. A tentative assignment of FTIR and Raman spectra of schafarzikite is given. Schafarzikite from Pernek most likely crystallized from late oxidizing hydrothermal fluids. Hence, it is not a weathering product, as assumed previously.