Bulletin Mineralogie Petrologie

A rare intermediate member of the scorodite - strengite series with an extraordinarily high degree of the anionic P for As substitution, technically a scorodite extremely rich in phosporus, scorodite₅₆ - strengite₄₁ (Scd₅₆ - Stg₄₁), was found and identified from mine dump material of the Rejzské pásmo Lode of the Kutná Hora ore district, Czech Republic. The mineral forms fine-grained, light brownish yellow crystalline masses and coatings, several milimeters in thickness on areas of tens of cm² on the surface of drusy quartz gangue with partially corroded galena and arsenopyrite. Chemical analyses revealed substantial amount of anionic phosphorus substituting for arsenic, ranging from 39.0 to 44.1 at. % of P (mean 41.0 %). Its chemical composition (mean of nine point analyses) corresponds to the empirical formula (Fe³⁺_0.93Al_0.03Pb_0.01)_Σ0.97[(As_0.56P_0.41S_0.03)_Σ1.00O_4.00]·2H₂O. Such a scope of the P for As substitution in members of the scorodite - strengite series is rare and exceptional. X-ray powder diffraction data, unit-cell parameters and space group for the intermediate member are reported [a = 8.844(2) Å, b = 9.969(2) Å, c = 10.247(2) Å, unit-cell volume V = 903.39 ų, Z = 8 and space group Pbca]. No discontinuation of the solid solution between scorodite and strengite has been observed, X-ray powder difraction analysis unambiguously confirmed the existence of a single phase representing an intermediate member.

Boultif A, Louër D (2004) Powder pattern indexing with the di­chotomy method. J Appl Crystallogr 37: 724-731. https://doi.org/10.1107/s0021889804014876  

Endo S, Terada Y, Kato Y, Nakai I (2008) Chemical speciation of arsenic-accumulating mineral in a sedimentary iron deposit by synchrotron radiation multiple X-ray analytical techniques. Environ Sci Technol 42: 7152-7158. https://doi.org/10.1021/es8006518

Kitahama K, Kiriyama R, Baba Y (1975) Refinement of the crystal structure of scorodite. Acta Crystallogr Sect B 31: 322-324. https://doi.org/10.1107/s056774087500266x

Llorens T, Moro MC (2012). Fe-Mn phosphate associations as indicators of the magmatic-hydrothermal and supergene evolution of the Jálama batholith in the Navasfrías Sn-W District, Salamanca, Spain. Mineral Mag 76: 1-24. https://doi.org/10.1180/minmag.2012.076.1.1

Murciego A, Pellitero Pascual E, Angeles Rodríguez M, Álvarez Ayuso E, García Sánchez A, Rubio F, Rubio J (2009) Arsenopyrite weathering products in Barruecopardo mine tailings (Salamanca, Spain). Revista Sociedad Esp Miner 11: 133-134

Murciego A, Álvarez-Ayuso E, Pellitero E, Rodríguez M, García-Sánchez A, Tamayo A, Rubio J, Rubio F, Rubio J (2011). Study of arsenopyrite weathering products in mine wastes from abandoned tungsten and tin exploitations. J Hazard Mater 186: 590-601. https://doi.org/10.1016/j.jhazmat.2010.11.033

Pauliš P, Dolníček Z, Gramblička R, Pour O (2020) Unusual vein Cu-Zn-Ag-Pb-As-Sb-Se-Sn-Bi mineralization from Jedová jáma mine near Vejprty in the Krušné hory Mts. (Czech Republic). Bull Mineral Petrol 28: 385-405 (in Czech with English abstract). https://doi.org/10.46861/bmp.28.385

Pouchou J, Pichoir F (1985) „PAP“ (jrz) procedure for improved quantitative microanalysis. In: Armstrong JT (ed): Microbeam Analysis: 104-106. San Francisco Press. San Francisco

Smith GS, Snyder RL (1979) F_N: A criterion for rating powder diffraction patterns and evaluating the reliability of powder indexing. J Appl Crystallogr 12: 60-65. https://doi.org/10.1107/s002188987901178x

Taxer K, Bartl H (2004) On the dimorphy between the variscite and clinovariscite group: refined finestructural relationship of strengite and clinostrengite, Fe(PO₄)·2H₂O. Cryst Res Technol 39: 1080-1088. https://doi.org/10.1002/crat.200410293