Skip to main content Accesibility Help

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

  • L. Bindi (a1) (a2), F. Nestola (a3), S. Graeser (a4), P. Tropper (a5) and T. Raber (a6)...

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 R min and R max 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 [R 1 = 0.0769 for 1606 reflections with F o > 4σ(F o)] 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/I 0) (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.

Corresponding author
Hide All
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, 212219.
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, 321333.
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, 17251729.
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, 851860.
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, 5158.
Brese, N.E. and O’Keeffe, M. (1991) Bond-valence parameters for solids. Acta Crystallographica, B47, 192197.
Chutas, N.I. and Sack, R.O. (2004) Ore genesis at La Colorada Ag-Zn-Pb deposit in Zacatecas, Mexico. Mineralogical Magazine, 68, 923937.
Engel, P. and Nowacki, W. (1968) Die Kristallstruktur von Ag3AsS3. Acta Crystallographica, B24, 7781.
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, 447456.
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.
Graeser, S., Cannon, R., Drechsler, E., Raber, T. and Roth, P. (2008) Faszination Lengenbach Abbau-Forschung-Mineralien 1958-2008. Kristallographik Verlag, Achberg, Germany.
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, 709719.
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, 43514365.
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, 319339.
Ibers, J.A. and Hamilton, W.C. (editors) (1974) International Tables for X-ray Crystallography, Vol. 4. Kynock, Dordrecht, The Netherlands, pp. 366.
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, 241253.
Kutoglu, A. (1968) Die Struktur des Pyrostilpnits (Feuerblende) Ag3SbS3. Neues Jahrbuch für Mineralogie, Monatshefte, 145160.
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, 486491.
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, 15291559.
Oxford Diffraction (2006) CrysAlis RED (Version and ABSPACK in CrysAlis RED. Oxford Diffraction Ltd, Abingdon, Oxfordshire, England.
Pfitzner, A. and Bernert, T. (2004) The system Cu3AsS4–Cu3SbS4 and investigations on normal tetra hedral structures. Zeitschrift für Kristallographie, 219, 2026.
Roth, P., Raber, T., Drechsler, E. and Cannon, R. (2014) The Lengenbach quarry, Binn Valley, Switzerland. Mineralogical Record, 45, 157196.
Sheldrick, G.M. (2008) A short history of SHELX. Acta Crystallographica, A64, 112122.
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, 757760.
Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Mineralogical Magazine
  • ISSN: 0026-461X
  • EISSN: 1471-8022
  • URL: /core/journals/mineralogical-magazine
Please enter your name
Please enter a valid email address
Who would you like to send this to? *


Type Description Title
Supplementary materials

Bindi et al. supplementary material
Structure factors

 Unknown (81 KB)
81 KB
Supplementary materials

Bindi et al. supplementary material

 Unknown (13 KB)
13 KB


Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed