Fassinaite, Pb 2 2+ (S 2 O 3 )(CO 3 ), the first mineral with coexisting thiosulphate and carbonate groups: description and crystal structure L. BINDI 1,2, *, F. NESTOLA 3 , U. KOLITSCH 4,5 , A. GUASTONI 6 AND F. ZORZI 3 1 Museo di Storia Naturale, Sezione Mineralogia e Litologia, Universita ` degli Studi di Firenze, Via G. La Pira 4, I-50121 Firenze, Italy 2 CNR Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via G. La Pira 4, I-50121 Firenze, Italy 3 Dipartimento di Geoscienze, Universita ` degli Studi di Padova, Via Gradenigo 6, I-35131 Padova, Italy 4 Naturhistorisches Museum, Mineralogisch-Petrographische Abt., Burgring 7, A-1010 Wien, Austria 5 Institut fu ¨r Mineralogie und Kristallographie, Geozentrum, Universita ¨t Wien, Althanstrasse 14, A-1090 Wien, Austria 6 Museo di Mineralogia, Universita ` degli Studi di Padova, Palazzo Cavalli, Via Matteotti 30, I-35121, Padova, Italy [Received 12 July 2011; Accepted 18 September 2011] ABSTRACT Fassinaite, ideally Pb 2 2+ (S 2 O 3 )(CO 3 ), is a new mineral from the Trentini mine, Mount Naro, Vicenza Province, Veneto, Italy (holotype locality). It is also reported from the Erasmus adit, Schwarzleo District, Leogang, Salzburg, Austria and the Friedrich-Christian mine, Schapbach, Black Forest, Baden- Wu ¨rttemberg, Germany (cotype localities). At the Italian type locality it occurs as acicular [010], colourless crystals up to 200 mm long, closely associated with galena, quartz and anglesite. At the Austrian cotype locality it is associated with cerussite, rare sulphur and very rare phosgenite. At the German cotype locality anglesite is the only associated phase. Fassinaite crystals commonly have flat chisel-shaped terminations. They are transparent with vitreous to adamantine lustre and a white streak. Fassinaite is brittle with an irregular fracture and no discernible cleavage; the estimated Mohs hardness is 1Ý 2. The calculated density for the type material is 6.084 g cm 3 (on the basis of the empirical formula), whereas the X-ray density is 5.947 g cm 3 . In common with other natural lead thiosulphates (i.e. sidpietersite and steverustite) fassinaite has intense internal reflections, which do not allow satisfactory optical data to be collected; the crystals are length-slow and have very high birefringence. The mineral is not fluorescent. Fassinaite is orthorhombic, space group Pnma, with unit-cell parameters (for the holotype material) a = 16.320(2), b = 8.7616(6), c = 4.5809(7) A ˚ , V = 655.0(1) A ˚ 3 , a:b:c = 1.863:1:0.523, Z = 4. Single- crystal structural studies were carried out on crystals from all three localities: R 1 (F) values range between 0.0353 and 0.0596. The structure consists of rod-like arrangements of Pb-centred polyhedra that extend along the [010] direction. These ‘rods’ are linked, alternately, by (CO 3 ) 2 and (S 2 O 3 ) 2 groups. The (S 2 O 3 ) 2 groups point alternately left and right (in a projection on [001] with [010] set vertical) if the apex occupied by the S 2 in the thiosulphate group is defined to be the atom giving the direction. The lead atoms are nine-coordinated by seven oxygen atoms and two sulphur (S 2 ) atoms. The eight strongest X-ray powder-diffraction lines [d in A ˚ (I/I 0 )(hkl)] are: 4.410 (39) (101), 4.381 (59) (020), 4.080 (62) (400), 3.504 (75) (301), 3.108 (100) (121), 2.986 (82) (420), 2.952 (49) (221) and 2.736 (60) (321). Electron-microprobe analyses produce an empirical formula Pb 2.01(1) (S 1.82(2) O 3 )CO 3 (on the basis of six oxygen atoms). The presence of both carbonate and thiosulphate groups was corroborated by Raman spectra, which are discussed in detail. Fassinaite is named after Bruno Fassina (b. 1943), an Italian mineral collector who discovered the mineral in 2009. KEYWORDS: fassinaite, new mineral, crystal structure, Raman spectroscopy, thiosulphate, Trentini mine, Erasmus adit, Friedrich-Christian mine. Introduction THIOSULPHATES were identified as weathering products by Braithwaite et al. (1993) who * E-mail: luca.bindi@unifi.it DOI: 10.1180/minmag.2011.075.6.2721 Mineralogical Magazine, December 2011, Vol. 75(6), pp. 2721–2732 # 2011 The Mineralogical Society