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

Authors: Sejkora, Jiří; Ozdín, Daniel; Vitáloš, Jiří; Tuček, Peter; Čejka, Jiří; Ďuďa, Rudolf

Source: European Journal of Mineralogy, Volume 19, Number 3, May 2007 , pp. 419-427(9)

Publisher: E. Schweizerbart'sche Verlagsbuchhandlung

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Abstract:

A rare mineral schafarzikite, an oxide of Fe²⁺ and Sb³⁺, was found after more than 80 years at the type locality near Pernek (Malé 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 {100} cleavage and perfect cleavage along unindexed planes parallel to z axis, tenacity-brittle; VHN_10g micro-hardness = 251 and 278 kp/mm² (for two cuts with differing orientation), corresponding to Mohs' hardness of 3.5-4; calculated density D_x = 5.507 g/cm³. 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(Sb_1.99As_0.02)_Σ2.01O₄. The XRD pattern was indexed in a tetragonal setting, with refined unit-cell parameters are a = 8.6073(2), c = 5.9093(3) Å, V = 437.80(2) Å³, c : a = 0.6865. Thermogravimetric (TG) curve shows mass gain of 1.62 wt. % in the range 20-580 °C, and 5.28 wt. % in the range 580-850 °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.

Keywords: SCHAFARZIKITE; X-RAY DIFFRACTION; THERMOGRAVIMETRY BEHAVIOR; INFRARED SPECTROSCOPY; RAMAN SPECTROSCOPY; SB-DEPOSIT PERNEK

Document Type: Research article

DOI: http://dx.doi.org/10.1127/0935-1221/2007/0019-1723

Publication date: 2007-05-01

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