The new mineral species marcobaldiite, ∼Pb12(Sb3As2Bi)Σ6S21, has been discovered in a single specimen collected in a quartz vein embedded in tourmaline-bearing schist from the Pollone mine, Valdicastello Carducci, Pietrasanta, Apuan Alps, Tuscany, Italy. It occurs as a black blocky prismatic crystal, up to 1 cm in size, with a metallic luster, associated with Sb-rich tennantite. Under the ore microscope, marcobaldiite is white, with a distinct anisotropism, with grey to bluish-grey rotation tints. Polysynthetic lamellar twinning is common and characteristic. Reflectance percentages for the four COM wavelengths are [Rmin, Rmax (%), (λ)]: 31.6, 40.1 (470 nm), 30.9, 39.6 (546 nm), 30.4, 38.5 (589 nm), and 30.0, 37.6 (650 nm). Electron microprobe analyses gave (average of 10 spot analyses − in wt%): Pb 64.05(34), Bi 4.24(6), Sb 9.10(14), As 4.51(8), S 17.24(19), total 99.14(53). On the basis of ΣMe = 18 apfu, the empirical formula is Pb11.98(4)Sb2.90(3)As2.33(3)Bi0.79(1)S20.80(20). The main diffraction lines, corresponding to multiple hkl indices, are [d in Å (relative visual intensity)]: 3.568 (ms), 3.202 (ms), 3.016 (ms), 2.885 (ms), 2.233 (vs), 2.125 (s), 1.848 (s), and 1.775 (s). The crystal structure study gives a triclinic unit cell, space group P, with a = 8.9248(9), b = 29.414(3), c = 8.5301(8) Å, α = 98.336(5), β = 118.175(5), γ = 90.856(5)°, V = 1944.1(3) Å3, Z = 2. The crystal structure has been solved and refined to R1 = 0.067 on the basis of 6188 reflections with Fo > 4σ(Fo) and 363 refined parameters. Marcobaldiite is a new N = 3.5 homologue of the jordanite homologous series, characterized by the 1:1 alternation of two kinds of layers of distorted octahedra, three- and four-octahedra thick, i.e. of the kirkiite and jordanite types, respectively. Layers are connected by one atomic layer of three bicapped trigonal prismatic Pb atoms and one triangular pyramidal As atom in split position. The name of this new mineral species honours the mineral amateur Marco Baldi (b. 1944) for his contribution to the knowledge of the mineralogy of the pyrite ± baryte ± iron oxide ore deposits from southern Apuan Alps.
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Research Article|
May 01, 2018
Lead-antimony sulfosalts from Tuscany (Italy). XXII. Marcobaldiite, ∼Pb12(Sb3As2Bi)Σ6S21, a new member of the jordanite homologous series from the Pollone mine, Valdicastello Carducci
Cristian Biagioni
;
1
Dipartimento di Scienze della Terra, Università di Pisa
, Via S. Maria 53, 56126Pisa, Italy
e-mail: cristian.biagioni@unipi.it
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Marco Pasero
;
Marco Pasero
1
Dipartimento di Scienze della Terra, Università di Pisa
, Via S. Maria 53, 56126Pisa, Italy
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Yves Moëlo
;
Yves Moëlo
2
Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS
, 2, rue de la Houssinière, BP 32229, 44322Nantes Cedex 3, France
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Federica Zaccarini
;
Federica Zaccarini
3
Resource Mineralogy, University of Leoben
, Peter Tunner Str. 5, 8700Leoben, Austria
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Werner H. Paar
Werner H. Paar
4
Department of Chemistry and Physics of Materials, University
, Jakob Haringerstr. 2a, 5020Salzburg, Austria
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European Journal of Mineralogy (2018) 30 (3): 581–592.
Article history
received:
04 Jul 2017
rev-recd:
13 Sep 2017
accepted:
15 Sep 2017
first online:
04 May 2018
Citation
Cristian Biagioni, Marco Pasero, Yves Moëlo, Federica Zaccarini, Werner H. Paar; Lead-antimony sulfosalts from Tuscany (Italy). XXII. Marcobaldiite, ∼Pb12(Sb3As2Bi)Σ6S21, a new member of the jordanite homologous series from the Pollone mine, Valdicastello Carducci. European Journal of Mineralogy 2018;; 30 (3): 581–592. doi: https://doi.org/10.1127/ejm/2018/0030-2710
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Index Terms/Descriptors
- antimony
- Apennines
- Apuane Alps
- arsenic
- bismuth
- cell dimensions
- coordination
- crystal structure
- electron probe data
- Europe
- homology
- Italy
- jordanite
- lead
- metals
- new minerals
- octahedra
- polyhedra
- quartz veins
- refinement
- reflectance
- Southern Europe
- sulfarsenites
- sulfosalts
- Tuscany Italy
- twinning
- veins
- X-ray diffraction data
- Valdicastello Carducci Italy
- Pollone Mine
- Pietrasanta Italy
- marcobaldiite
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