Bonacinaite, Sc(AsO₄) · 2H₂O, the first scandium arsenate

Autor(en)

Marco E. Ciriotti, Uwe Kolitsch, Fernando Cámara, Pietro Vignola, Frédéric Hatert, Erica Bittarello, Roberto Bracco, Giorgio Maria Bortolozzi

Abstrakt

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)_Ʃ1.00[(As_0.95P_0.06)_Ʃ1.01O₄] · 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(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

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

Band

36

Seiten

863-872

Anzahl der Seiten

10

ISSN

0935-1221

DOI

https://doi.org/10.5194/ejm-36-863-2024

Publikationsdatum

09-2024

Peer-reviewed

Ja

ÖFOS 2012

105116 Mineralogie, 105113 Kristallographie

ASJC Scopus Sachgebiete

Geochemistry and Petrology

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/584f4b8c-c330-463b-9afe-4debadd83690