Original paper

Jaszczakite, [(Bi, Pb)3 S3][AuS2], a new mineral species from Nagybörzsöny, Hungary

Bindi, Luca; Paar, Werner H.

European Journal of Mineralogy Volume 29 Number 4 (2017), p. 673 - 677

published: Sep 1, 2017

DOI: 10.1127/ejm/2017/0029-2620

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Abstract

Jaszczakite, [(Bi, Pb)3 S3 ][AuS2], represents another new species from the abandoned Nagybörzsöny Au deposit at AlsóRózsa, northern Hungary. The mineral is closely associated with arsenopyrite, pyrite, marcasite, sphalerite, chalcopyrite, gold, bismuth, bismuthinite, ikunolite, jonassonite, and cosalite, in a matrix of quartz. It is opaque, tin-white, has a metallic lustre and a black streak. Jaszczakite is brittle, and the fracture is irregular. Neither cleavage nor parting are observable in the section. The VHN5 value ranges between 115 and 132 (mean 122) kg mm2 which corresponds to a Mohs hardness of 2½–3. The calculated density is 7.327 g cm3. In plane-polarized light jaszczakite is weakly bireflectant and pleochroic from light grey to a slightly bluish grey. Internal reflections are absent. The mineral is distinctly anisotropic with rotation tints very similar to those of jonassonite (shades of green and purple). The reflectance COM values (air, R 1 and R 2 in %) are: 49.4, 50.9 (471.1 nm); 47.1, 48.8 (548.3 nm); 46.5, 47.7 (586.6 nm); 48.8, 49.5 (652.3 nm). The average result of five electron-microprobe analyses is Au 19.90(34), Ag 0.22(3), Bi 46.29(54), Pb 16.50(26), Cd 0.11(3), Sb 0.12(4), As 0.08(3), S 16.17(30), Se 0.16(6), total 99.55 wt%. The empirical formula (based on 9 atoms pfu) is Au1.00 Ag0.02 Bi2.18 Pb0.78 Cd0.01 Sb0.01 As0.01 S4.97 Se0.02 or, according to the refinement results, [(Bi2.18 Pb0.78 Ag0.02 Cd0.01 Sb0.01 As0.01)S=3.01 S3][AuS2]. The simplified formula is AuBi3 S5, which requires Au 20.01, Bi 63.70, S 16.29, total 100.00 wt%. Jaszczakite is orthorhombic, space group Pmmn, with unit-cell parameters: a = 3.858(1), b = 12.552(3), c = 9.289(2) Å, V = 449.83(8) Å3, a: b : c = 0.3074:1:0.7400, Z = 2. The five strongest observed X-ray powder-diffraction lines [ d in Å (I/I 0) (hkl)] are: 7.466 (100) (011), 6.2760 (90) (020), 5.2003 (24) (021), 3.0963 (68) (003), 2.7768 (26) (023). The crystal structure showed that jaszczakite is the S– Bi-analogue of buckhornite [Pb2 BiS3 ][AuTe2]. Jaszczakite is named in honour of John A. Jaszczak, Professor of Physics at the Michigan Technological University, for his significant contributions on the complexities of natural graphite.

Keywords

northern hungarybismuth–lead–gold–sulfidecrystal structurenew mineralreflectance datanagybörzsöny au depositelectron-microprobe analysesalsó;-rózsajaszczakite