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Mercury-arsenic sulfosalts from the Apuan Alps (Tuscany, Italy). II. Arsiccioite, AgHg2TlAs2S6, a new mineral from the Monte Arsiccio mine: occurrence, crystal structure and crystal chemistry of the routhierite isotypic series

Published online by Cambridge University Press:  05 July 2018

C. Biagioni*
Affiliation:
Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56126 Pisa, Italy
E. Bonaccorsi
Affiliation:
Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56126 Pisa, Italy
Y. Moëlo
Affiliation:
Institut des Matériaux Jean Rouxel, UMR 6502, CNRS, Université de Nantes, 2, rue de la Houssinière, 44322 Nantes Cedex 3, France
P. Orlandi
Affiliation:
Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56126 Pisa, Italy Istituto di Geoscienze e Georisorse, CNR, Via Moruzzi 1, I-56124 Pisa, Italy
L. Bindi
Affiliation:
Dipartimento di Scienze della Terra, Università di Firenze, Via G. La Pira 4, I-50121 Florence, Italy
M. D’Orazio
Affiliation:
Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56126 Pisa, Italy
S. Vezzoni
Affiliation:
Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56126 Pisa, Italy

Abstract

The new mineral species arsiccioite, AgHg2TlAs2S6, was discovered in the baryte-pyrite-iron oxide ore deposit exploited at the Monte Arsiccio mine, near Sant’Anna di Stazzema (Apuan Alps, Tuscany, Italy). It occurs as anhedral grains scattered in microcrystalline baryte, associated with cinnabar, laffittite, protochabournéite, pyrite, realgar, Hg-bearing sphalerite and stibnite. Arsiccioite is red, with a metallic to sub-metallic lustre. Minimum and maximum reflectance data for COM wavelengths in air are [λ (nm): R (%)]: 471.1: 29.0/29.4; 548.3: 27.6/28.3; 586.6: 26.1/26.5; 652.3: 24.2/24.6. Electron microprobe analyses give (wt.%): Cu 0.78(6), Ag 8.68(21), Zn 0.47(27), Fe 0.04(1), Hg 35.36(87), Cd 0.20(5), Tl 18.79(33), As 10.77(19), Sb 4.75(10), S 18.08(21), Se 0.07(5), total 97.99(44). On the basis of ΣMe = 6 a.p.f.u., the chemical formula is Ag0.87(2)Cu0.13(1)Zn0.08(4)Fe0.01(1)Hg1.91(5)Cd0.02(1)Tl1.00(2) (As1.56(2)Sb0.42(1))S1.98S6.12(6)Se0.01(1). Arsiccioite is tetragonal, I 2m, with a 10.1386(6), c 11.3441(5) Å, V 1166.1(2) Å3, Z = 4. The main diffraction lines of the powder diagram are [d(in Å), visually estimated intensity, hkl]: 4.195, m, 211; 3.542, m, 103; 3.025, vs, 222; 2.636, m, 114; 2.518, s, 400 and 303. The crystal structure of arsiccioite has been refined by single-crystal X-ray data to a final R 1 = 0.030, on the basis of 893 observed reflections. It shows a three dimensional framework of (Hg,Ag)- centred tetrahedra (1 M1 + 2 M2), with channels parallel to [001] hosting TlS6 and (As,Sb)S3 disymmetric polyhedra. Arsiccioite is derived from its isotype routhierite M1CuM2Hg2TlAs2S6 through the double heterovalent substitution M1Cu+ + M2Hg2+ → M1Hg2+ + M2Ag+. This substitution obeys a steric constraint, with Ag+, the largest cation relative to Hg2+ and Cu+, entering the largest M2 site. The ideal crystal chemical formula of arsiccioite is M1HgM2(Hg0.5Ag0.5)2TlAs2S6. The crystal chemistry of the routhierite isotypic series is discussed. Finally, the distribution of Hg ore minerals in the Apuan Alps is reviewed.

Information

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2014

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