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Mineralogy and Petrology Title Cervelleite, Ag4TeS: solution and description of the crystal structure Authors Bindi, L; Spry, PG; Stanley, Christopher Date Submitted 2016-03-15 Mineralogy and Petrology Cervelleite, Ag4TeS: solution and description of the crystal structure --Manuscript Draft-- Manuscript Number: MIPE-D-15-00008R1 Full Title: Cervelleite, Ag4TeS: solution and description of the crystal structure Article Type: Standard Article Keywords: cervelleite; Ag-Te-S system; Ag-Cu sulfotellurides; crystal structure; aguilarite; acanthite Corresponding Author: Luca Bindi, Prof University of Florence Florence, ITALY Corresponding Author Secondary Information: Corresponding Author's Institution: University of Florence Corresponding Author's Secondary Institution: First Author: Luca Bindi, Prof First Author Secondary Information: Order of Authors: Luca Bindi, Prof Christopher Stanley Paul G Spry Order of Authors Secondary Information: Funding Information: Abstract: Examination of the type specimen of cervelleite throws new light on its structure demonstrating how earlier researchers erred in describing the mineral as cubic. It was found to be monoclinic, space group P21/n, with a = 4.2696(4), b = 6.9761(5), c = 8.0423(7) Å, β = 100.332(6)°, V = 235.66(3) Å3, Z = 4. The crystal structure [R1 = 0.0329 for 956 reflections with I > 2σ(I)] is topologically identical to that of acanthite, Ag2S, and aguilarite, Ag4SeS. It can be described as a body-centered array of tetrahedrally coordinated X atoms (where X = S and Te) with Ag2X4 polyhedra in planes nearly parallel to (010); the sheets are linked by the other silver position (i.e., Ag1) that exhibits a three-fold coordination. Crystal-chemical features are discussed in relation to other copper and silver sulfides/tellurides, and pure metals. A SEM study of the cervelleite crystal used for the structural investigation showed that it is intergrown with an unnamed Ag2FeS2 phase in the type material. Response to Reviewers: Dear Anton, Please find herewith the revised copy of the manuscript entitled “Cervelleite, Ag4TeS: solution and description of the crystal structure” by Luca Bindi, Christopher J. Stanley, and Paul G. Spry. We did the minor stylistic changes suggested by the reviewers. We think that it is not necessary to add the Table as suggested by Rev#2. With best regards, Luca Bindi Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Manuscript Click here to download Manuscript: MIPE-D-15-00008_text.doc 1 1 2 3 4 5 6 7 8 Cervelleite, Ag4TeS: solution and description of the crystal 9 10 structure 11 12 13 14 15 L. Bindi a C.J. Stanley b P.G. Spry c 16 17 18 19 20 21 a 22 Dipartimento di Scienze della Terra, Università di Firenze, Via G. La Pira 4, I-50121Firenze, Italy 23 24 b 25 Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, United 26 27 Kingdom 28 29 c 30 Department of Geological and Atmospheric Sciences, 253 Science I, Iowa State University, Ames, 31 Iowa 50011-3212, U.S.A. 32 33 34 35 36 37 38 Corresponding author: 39 40 Luca Bindi 41 42 Dipartimento di Scienze della Terra, 43 Università di Firenze 44 Via G. La Pira 4, I-50121 Firenze, Italy 45 46 Tel. +39-055-2757532 47 Fax +39-055-2757455 48 49 e-mail: [email protected] 50 51 52 53 54 55 Keywords: cervelleite Ag-Te-S system - crystal structure 56 57 aguilarite acanthite 58 59 60 61 62 63 64 65 2 Abstract 1 2 3 Examination of the type specimen of cervelleite throws new light on its structure 4 5 demonstrating how earlier researchers erred in describing the mineral as cubic. It 6 7 was found to be monoclinic, space group P2 /n, with a = 4.2696(4), b = 6.9761(5), c 8 1 9 3 10 = 8.0423(7) Å, β = 100.332(6)°, V = 235.66(3) Å , Z = 4. The crystal structure [R1 = 11 12 0.0329 for 956 reflections with I > 2σ(I)] is topologically identical to that of acanthite, 13 14 15 Ag2S, and aguilarite, Ag4SeS. It can be described as a body-centered array of 16 17 tetrahedrally coordinated X atoms (where X = S and Te) with Ag2X4 polyhedra in 18 19 20 planes nearly parallel to (010); the sheets are linked by the other silver position (i.e., 21 22 Ag1) that exhibits a three-fold coordination. Crystal-chemical features are discussed 23 24 25 in relation to other copper and silver sulfides/tellurides, and pure metals. A SEM 26 27 study of the cervelleite crystal used for the structural investigation showed that it is 28 29 intergrown with an unnamed Ag FeS phase in the type material. 30 2 2 31 32 33 34 35 Introduction 36 37 Silver chalcogenides have received much attention in recent years because of 38 39 40 their important technological applications (e.g., Padma Kumar and Yashonath 2006). 41 42 These compounds are known to be fast ionic conductors or semiconductors and, as 43 44 such, find practical applications in silver photography as sensitizers or in optics and 45 46 47 microelectronics as rewritable storage media. From a geological standpoint, silver 48 49 sulfotellurides are trace constituents accompanying native gold and Au-Ag-tellurides 50 51 52 in various deposit types that span the magmatic-hydrothermal spectrum. 53 54 In the system Ag-Te-S, cervelleite Ag4TeS is of particular interest because it 55 56 57 occurs as an accessory mineral in a range of hydrothermal precious mineral deposits 58 59 (Cook and Ciobanu 2003). It was defined as a new mineral species by Criddle et al. 60 61 62 63 64 65 3 (1989) during a study of ore minerals collected from the spoil tips of the abandoned 1 2 Bambolla mine, Moctezuma, Sonora (Mexico). By means of X-ray photographic 3 4 5 techniques, these authors studied fragments of cervelleite intergrown with acanthite 6 7 from a structural point of view and reported a cubic symmetry (with P23, Pm3, P432, 8 9 10 P43m, Pm3m, P213, P4232, P4132, P4332, Pa3 as possible space groups) with a = 11 12 14.03(1) and Z = 24. Criddle et al. (1989) also noticed that cervelleite, acanthite and 13 14 hessite were altered rapidly and profoundly by light, in a surface reaction interpreted 15 16 17 as photo-chemical in origin. 18 19 Cervelleite, along with other cervelleite-like minerals, has been reported from 20 21 22 various ore types including the intrusion-hosted San Martin deposit, Argentina (Paar 23 24 and De Brodtkorb 1996), the epithermal Mayflower Au-Ag deposit, Montana (Spry 25 26 27 and Thieben 1996), the Um Samiuki volcanogeneic massive sulfide deposit, Egypt 28 29 (Helmy 1999), epithermal (Larga, Roşia Montană) and skarn (Băiţa Bihor and Ocna 30 31 de Fier) occurrences in Romania (Cook and Ciobanu 2003; Ciobanu et al. 2004), the 32 33 34 Eniovche epithermal deposit, Bulgaria (Dobrev et al. 2002), the intrusion-hosted 35 36 Funan Au deposit, China (Gu et al. 2003), and several volcanic-hosted massive 37 38 39 sulfide deposits in the southern Urals (Novoselov et al. 2006). Unnamed Ag- 40 41 sulfotellurides [(Ag,Cu)6TeS2 – (Ag,Cu)4TeS] were described from the Funan deposit 42 43 44 (Gu et al. 2003), and a phase with the composition Ag2Cu2TeS was reported by Cook 45 46 and Ciobanu (2003) from the Băiţa Bihor and Ocna de Fier skarns in Romania. In 47 48 49 Greece, cuprian cervelleite and unnamed Ag-Cu sulfotellurides [(Ag,Cu)12Te3S2 and 50 51 (Ag,Au,Cu)9Te2S3] were described from the intrusion-related deposit at Panormos 52 53 Bay, Tinos Island (Tombros et al. 2004, 2010; Spry et al. 2006). In the Kallianou area 54 55 56 (southern Evia Island, Greece), gold-bearing quartz veins contain an exotic ore 57 58 mineralogy including cervelleite-like sulfotellurides [Ag2CuTeS and (Ag,Cu)2Te] and 59 60 61 62 63 64 65 4 Te-rich polybasite (Voudouris and Spry 2008; Voudouris et al. 2011; Bindi et al. 1 2 2013b). 3 4 5 In the course of a research project dealing with the description and structural 6 7 characterization of natural copper and silver tellurides (Bindi 2008, 2009, 2014; Bindi 8 9 10 and Cipriani 2004; Bindi and Pinch 2014; Bindi and Pingitore 2013; Bindi et al. 2004, 11 12 2005, 2009, 2013a, 2013b), we have examined a fragment of cervelleite from the 13 14 holotype material (catalogue number E.1161 BM 1985, 354). 15 16 17 18 19 20 The holotype 21 22 The specimen was collected by the late Alan Criddle on a field excursion to the 23 24 25 Sonora Desert led by the late Sid Williams. It consists of black powdery crusts (1–2 26 27 mm thick) of benleonardite, acanthite, hessite and cervelleite, together with gangue 28 29 quartz and dolomite (Fig. 1). The hessite contains a vermiform or myrmekitic 30 31 32 intergrowth of fine-grained cervelleite (pale-greenish-grey in Fig. 1). The assemblage 33 34 occupies irregular fractures in a highly altered rock described by Williams (1982) as 35 36 37 an intensely silicified rhyolitic vitrophyre. 38 39 40 41 42 Crystal-structure solution and refinement 43 44 A small crystal fragment (40 × 55 × 60 μm) was selected from the type 45 46 47 specimen for the X-ray single-crystal diffraction study that was done with an Oxford 48 49 Diffraction Xcalibur 3 CCD single-crystal diffractometer (Table 1). Surprisingly, most 50 51 52 of the X-ray reflections (89% of the total) match the following monoclinic unit cell: a ~ 53 54 4.30, b ~ 6.98, c ~ 8.04 Å and β ~ 100°, being very close to those of acanthite, Ag2S 55 56 57 (Frueh 1958) and aguilarite (Bindi and Pingitore 2013).
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