Hostname: page-component-586b7cd67f-t8hqh Total loading time: 0 Render date: 2024-11-22T06:19:15.109Z Has data issue: false hasContentIssue false
  • English
  • Français

Eckerite, Ag2CuAsS3, a new Cu-bearing sulfosalt from Lengenbach quarry, Binn valley, Switzerland: description and crystal structure

Published online by Cambridge University Press:  02 January 2018

L. Bindi ,
F. Nestola ,
S. Graeser ,
P. Tropper  and
T. Raber
L. Bindi*
Affiliation:
Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira 4, I-50121 Firenze, Italy CNR - Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via G. La Pira 4, I-50121 Firenze, Italy
F. Nestola
Affiliation:
Dipartimento di Geoscienze, Università degli Studi di Padova, Via Gradenigo 6, I-35131 Padova, Italy
S. Graeser
Affiliation:
Mineralogisches Institut, Universität Basel, Bernoullistrasse 30, CH-4056 Basel, Switzerland
P. Tropper
Affiliation:
Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52f, A-6020 Innsbruck, Austria
T. Raber
Affiliation:
FGL (Forschungsgemeinschaft Lengenbach), Edith-Stein-Strasse 9, D-79110 Freiburg, Germany
*
*E-mail: [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

Eckerite, ideally Ag2CuAsS3, is a new mineral from the Lengenbach quarry in the Binn Valley, Valais, Switzerland. It occurs as very rare euhedral crystals up to 300 μm across associated with realgar, sinnerite, hatchite, trechmannite and yellow, fibrous smithite. In thick section eckerite is opaque with a metallic lustre and shows a dark orange-red streak. It is brittle; the Vickers hardness (VHN25) is 70 kg/mm2 (range: 64–78) (Mohs hardness of ∼2½–3). In reflected light, eckerite is moderately bireflectant and weakly pleochroic from light grey to a slightly bluish grey. Internal reflections are absent. Under crossed nicols, it is weakly anisotropic with greyish to light blue rotation tints. Reflectance percentages for Rmin and Rmax are 27.6, 31.7 (471.1 nm), 22.8, 26.1 (548.3 nm), 21.5, 24.5 (586.6 nm) and 19.4, 22.3 (652.3 nm), respectively.

Eckerite is monoclinic, space group C2/c, with a = 11.8643(3), b = 6.2338(1), c = 16.6785(4) Å, β = 110.842(3)°, V = 1152.81(5) Å3, Z = 8. The crystal structure [R1 = 0.0769 for 1606 reflections with Fo > 4σ(Fo)] is topologically identical to that of xanthoconite and pyrostilpnite. In the structure, AsS3 pyramids are joined by AgS3 triangles to form double sheets parallel to (001); the sheets are linked by Cu(Ag) atoms in a quasi-tetrahedral coordination. Among the three metals sites, Ag2 is dominated by Cu. The mean metal–S distances reflect well the Ag ↔ Cu substitution occurring at this site.

The eight strongest powder X-ray diffraction lines [d in Å (I/I0) (hkl)] are: 3.336 (70) (312); 2.941 (100) (314,114); 2.776 (80) (400,206); 2.677 (40) (312); 2.134 (50) (421); 2.084 (40) (208,206); 2.076 (40) (420); 1.738 (40) (228,226). A mean of five electron microprobe analyses gave Ag 52.08(16), Cu 11.18(9), Pb 0.04(1), Sb 0.29(3), As 15.28(11), S 20.73(13), total 99.60 wt.%, corresponding, on the basis of a total of 7 atoms per formula unit, to Ag2.24Cu0.82As0.94Sb0.01S2.99. The new mineral has been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (2014–063) and named for Markus Ecker, a well known mineral expert on the Lengenbach minerals for more than 25 years.

Keywords

eckeritenew mineralAg-sulfosaltsLengenbachSwitzerland
Type
Research Article
Information
Mineralogical Magazine , Volume 79 , Issue 3 , June 2015 , pp. 687 - 694
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2015

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Bindi, L., Evain, M. and Menchetti, S. (2006) Temperature dependence of the silver distribution in the crystal structure of natural pearceite, (Ag,Cu)16(As,Sb)2S11. Acta Crystallographica, B62, 212–219.CrossRefGoogle Scholar
Bindi, L., Evain, M. and Menchetti, S. (2007) Complex twinning, polytypism and disorder phenomena in the crystal structures of antimonpearceite and arsenpolybasite. The Canadian Mineralogist, 45, 321–333.CrossRefGoogle Scholar
Bindi, L., Pratesi, G. and Spry, P.G. (2010) Crystallographic and chemical constraints on the nature of the proustite-pyrargyrite solid solution series. American Mineralogist, 95, 1725–1729.CrossRefGoogle Scholar
Bindi, L., Makovicky, E., Nestola, F. and De Battisti, L. (2013) Sinnerite, Cu6As4S9, from Lengenbach quarry, Binn valley, Switzerland: Description and re-investigation of the crystal structure. The Canadian Mineralogist, 51, 851–860.CrossRefGoogle Scholar
Bindi, L., Nestola, F., Graeser, S., Tropper, P. and Raber, T. (2015) Eckerite, IMA 2014-063. CNMNC Newsletter No. 23, February 2015, page 52; Mineralogical Magazine, 79, 51–58.Google Scholar
Brese, N.E. and O’Keeffe, M. (1991) Bond-valence parameters for solids. Acta Crystallographica, B47, 192–197.CrossRefGoogle Scholar
Chutas, N.I. and Sack, R.O. (2004) Ore genesis at La Colorada Ag-Zn-Pb deposit in Zacatecas, Mexico. Mineralogical Magazine, 68, 923–937.CrossRefGoogle Scholar
Engel, P. and Nowacki, W. (1968) Die Kristallstruktur von Ag3AsS3. Acta Crystallographica, B24, 77–81.CrossRefGoogle Scholar
Evain, M., Bindi, L. and Menchetti, S. (2006) Structural complexity in minerals: twinning, polytypism and disorder in the crystal structure of polybasite, (Ag,Cu)16(Sb,As)2S11. Acta Crystallographica, B62, 447–456.CrossRefGoogle Scholar
Gaines, R.V., Skinner, H.C.W., Foord, E.E., Mason, B. and Rosenzweig, A. (1997) Dana’s New Mineralogy. 8th Edition. John Wiley & Sons, New York, USA.Google Scholar
Graeser, S., Cannon, R., Drechsler, E., Raber, T. and Roth, P. (2008) Faszination Lengenbach Abbau-Forschung-Mineralien 1958-2008. Kristallographik Verlag, Achberg, Germany.Google Scholar
Harlov, D.E. (1999) Thermochemistry of Ag-Cu exchange equilibria between proustite, sinnerite, and pearceite: Constraints on Ag-Cu and As-Sb mixing in pyrargyrite-proustite. European Journal of Mineralogy, 11, 709–719.CrossRefGoogle Scholar
Harlov, D.E. and Sack, R.O. (1995) Thermochemistry of Ag2S–Cu2S sulfide solutions: Constraints derived from coexisting Sb2S3-and As2S3-bearing sulfosalts. Geochimica et Cosmochimica Acta, 59, 4351–4365.CrossRefGoogle Scholar
Hofmann, B.A. and Knill, M.D. (1996) Geochemistry and genesis of the Lengenbach Pb-Zn-As-Tl-Ba mineralization, Binn Valley, Switzerland. Mineralium Deposita, 31, 319–339.CrossRefGoogle Scholar
Ibers, J.A. and Hamilton, W.C. (editors) (1974) International Tables for X-ray Crystallography, Vol. 4. Kynock, Dordrecht, The Netherlands, pp. 366.Google Scholar
Karanovic, L., Cvetkovic, L., Poleti, D., Balić-Žunić, T. and Makovicky, E. (2002) Crystal and absolute structure of enargite from Bor (Serbia). Neues Jahrbuch für Mineralogie, Monatshefte, 2002, 241–253.CrossRefGoogle Scholar
Kutoglu, A. (1968) Die Struktur des Pyrostilpnits (Feuerblende) Ag3SbS3. Neues Jahrbuch für Mineralogie, Monatshefte, 145–160.Google Scholar
Lange, B., Scholz, F., Bautsch, H.-J., Damaschun, F. and Wappler, G. (1993) Thermodynamics of the xanthoconite-proustite and pyrostilpnite-pyrargyrite phase transition as determined by abrasive stripping voltammetry. Physics and Chemistry of Minerals, 19, 486–491.CrossRefGoogle Scholar
Loucks, R.R. and Petersen, U. (1988) Polymetallic epithermal fissure vein mineralization, Topia, Durango, Mexico: Part II. Silver mineral chemistry and high resolution patterns of chemical zoning in veins. Economic Geology, 83, 1529–1559.CrossRefGoogle Scholar
Oxford Diffraction (2006) CrysAlis RED (Version 1.171.31.2) and ABSPACK in CrysAlis RED. Oxford Diffraction Ltd, Abingdon, Oxfordshire, England.Google Scholar
Pfitzner, A. and Bernert, T. (2004) The system Cu3AsS4–Cu3SbS4 and investigations on normal tetra hedral structures. Zeitschrift für Kristallographie, 219, 20–26.Google Scholar
Roth, P., Raber, T., Drechsler, E. and Cannon, R. (2014) The Lengenbach quarry, Binn Valley, Switzerland. Mineralogical Record, 45, 157–196.Google Scholar
Sheldrick, G.M. (2008) A short history of SHELX. Acta Crystallographica, A64, 112–122.CrossRefGoogle Scholar
Suh, In-Kook, Ohta, H. and Waseda, Y. (1988) Hightemperature thermal expansion of six metallic elements measured by dilatation method and X-ray diffraction. Journal of Materials Science, 23, 757–760.CrossRefGoogle Scholar
Supplementary material: File

Bindi et al. supplementary material

CIF

Download Bindi et al. supplementary material(File)
File 12.8 KB
Supplementary material: File

Bindi et al. supplementary material

Structure factors

Download Bindi et al. supplementary material(File)
File 81.2 KB