Mineralogy

Tetrahedrite

Structural info:

tetrahedrite3

Name origin:

Derived from its typical tetrahedron crystal shape.

Tetrahedrite is a copper antimony sulfosalt  with a formula Cu6[Cu4(Fe, Zn)2]Sb4S13. Ussualy copper atoms are substituted for other elements in the crystal structure. As the copper atoms can be easily substituted for iron, zincum, mercury or silver atoms a few varieties of the mineral are known:

  • Schwatzite (mercurian tetrahedrite) is named after the locality Schwaz  (Tyrol, Austria) where it was described for the first time. Its formula is (Cu,Hg)12Sb4S13.
  • Freibergite is a silver rich variety of tetrahedrite. The silver containg ranges from 18.5 % up to 42.5 % therefore it is often mined as a silver ore. A formula may be represented as (Cu,Ag)12Sb4S13 [1].
  • Zincian tetrahedrite with simplified formula Cu10Zn2Sb4S13 that is found in a certain Pb-Zn ore deposit at Mianning, Sichuan [2].

It belongs to Tetrahedrite Group. Tennantite-Tetrahedrite Series, and the Freibergite-Tetrahedrite Series. It is an opaque mineral with grey to black colour and black, brown or red streak. It has metallic luster. Tetraedrite is a brittle mineral with sub-conchoidal fracture and no cleavage. The crystals are often twinned.

The mineral possesses a cubic sphalerite-like structure. It contains two types of copper atoms in its crystal structure, the first type (Cu2+) exhibits tetrahedral coordination to one antimony and three sulfurs, while the second – monovalent – is three-fold planar coordinated with three sulfurs. Twelve of the 13 sulfur atoms in the formula unit are tetrahedrally coordinated whereas the sulfur atoms at the corners and in the center of the cube has six Cu neighbors [3].

tetrahedrite1

tetrahedrite2

Tetrahedrite crystals on matrix, Cavnic mine, Cavnic, Maramures Co., Romania (valued at 50 $) [photo: Michal Hegedus]

Literature:
[1] J.F. Riley. Mineralium Deposita. Vol. 9, Iss. 2, p. 117-124 (1974).
[2] Xu Shenglin. Acta Mineralogica Sinica. Vol. 10, No. 3, p. 232-234 (1990).
[1] Xu Lu et al. Advanced energy materials. Vol. 3, Iss. 3, p. 342-348 (2012).