Bonacinaite, Sc(AsO<sub>4</sub>) · 2H<sub>2</sub>O, the first scandium arsenate

Author(s): Marco E. Ciriotti, Uwe Kolitsch, Fernando Cámara, Pietro Vignola, Frédéric Hatert, Erica Bittarello, Roberto Bracco, Giorgio Maria Bortolozzi
Abstract: The new mineral bonacinaite (IMA2018-056), Sc(AsO₄) q 2H₂O, was found on the dumps of the Varenche Mine (Saint-Barthélemy, Nus, Aosta Valley, Italy), an old manganese mine, where it occurs as a low-temperature hydrothermal mineral associated mainly with quartz, granular braunite, undefined manganese oxides, arseniopleite, manganberzeliite and thortveitite. Bonacinaite forms colourless (with faint to distinct violet tints), pseudohexagonal, thick tabular crystals, up to 0.25 mm in size, sometimes with annular internal zones showing violet tinges, or as small, faintly violet lath-shaped crystals. The crystals are transparent and brittle, with vitreous lustre. The calculated density of an almost pure bonacinaite crystal is 2.82 g cm⁻³. Optically, bonacinaite is biaxial negative, α = 1.598(4), β = 1.618(3), and γ = 1.638(3) (measured with a Na light
source, 589 nm); 2V (measured) is large, and 2V (calculated) = −88.9°. The empirical formula, based on six O atoms per formula unit is (Sc_0.90Mn³⁺_0.08Fe³⁺_0.01Pb_0.01)_Ʃ_1.00[(As_0.95P_0.06)_Ʃ_1.01O₄] · 2H2O. Bonacinaite has monoclinic symmetry, with space group P 2₁/n and unit-cell parameters (single-crystal data / powder diffraction data) a = 5.533(1)/5.521(1), b = 10.409(2)/10.336(3), c = 9.036(2)/9.059(4) Å, β = 91.94(3)/91.97(4),
V = 520.1(2)/516.7(3) Å3 and Z = 4. The crystal structure was refined from single-crystal intensity data obtained from a distinctly Al- and P-bearing crystal to R₁(F) = 3.7 % for 1178 reflections. Bonacinaite is isotypic with the other members of the metavariscite group: kolbeckite, metavariscite and phosphosiderite.
Organisation(s): Department of Mineralogy and Crystallography
External organisation(s): Associazione Micromineralogica Italiana, Naturhistorisches Museum Wien (NHM), Istitutio di Geologia Ambientale e Geoingegneria, Università degli Studi di Torino, Università degli Studi di Milano-Bicocca, Université de Liège
Journal: European Journal of Mineralogy
Volume: 36
Pages: 863-872
No. of pages: 10
ISSN: 0935-1221
DOI: https://doi.org/10.5194/ejm-36-863-2024
Publication date: 09-2024
Peer reviewed: Yes
Austrian Fields of Science 2012: 105116 Mineralogy, 105113 Crystallography
ASJC Scopus subject areas: Geochemistry and Petrology
Portal url: https://ucrisportal.univie.ac.at/en/publications/bonacinaite-scaso4--2h2o-the-first-scandium-arsenate(584f4b8c-c330-463b-9afe-4debadd83690).html

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