Freieslebenite

Freieslebenite

Freieslebenite from Hiendelaencina, Spain. Exposed in the Mineralogical Museum, Bonn, Germany
General
Category Sulfosalt minerals
Formula
(repeating unit)		 AgPbSbS3
Strunz classification 02.JB.15
Crystal symmetry Monoclinic prismatic
H-M symbol (2/m)
Space group: P 21/n
Unit cell a = 7.518(1) Å, b = 12.809(4) Å, c = 5.940(1) Å; β = 92.25(1)°; Z=4
Identification
Color Pale steel-gray to silver-white or lead-gray
Crystal habit Striated, prismatic crystals, inclusions and exsolutions in galena and other silver minerals
Crystal system Monoclinic
Twinning Twin plane {010}
Cleavage {110} Indistinct
Fracture Brittle-conchoidal
Mohs scale hardness 2.5
Luster Metallic
Streak Whitish-gray
Diaphaneity Opaque
Specific gravity 6.20-6.23
Pleochroism Very weak
References [1][2][3]

Freieslebenite is a sulfosalt mineral composed of antimony, lead, and silver. Sulfosalt minerals are complex sulfide minerals with the formula: AmBnSp. The formula of freieslebenite is AgPbSbS3.

Freieslebenite was discovered in approximately 1773 in the Himmelsfurst mines of Freiberg, Saxony, Germany. The mineral was initially called Schilf-Glaserz; however, in 1845 it was given the current name Freieslebenite after the Mining Commissioner of Saxony, Johann Carl Freiesleben (1774–1846).[4]

Structure

Freieslebenite is a superstructure of a PbS-type substructure. The crystal structure is monoclinic with a space group P21/a, with a = 7.518(1), b = 12.809(4), c = 5.940(1) Å, β = 92.25(1)° and Z = 4(Ito, 1973). Sb has a trigonal-pyramidal coordination of S atoms, this structure isolates the SbS3 pyramids from themselves. The Sb–S distances are 2.431, 2.453 and 2.480(4) Å. Six S atoms are coordinated with Pb in a distored octahedral arrangement. The Pb–S distances range from 2.806 to 3.167(4) Å. Ag has three nearest S neighbors at the distances 2.522, 2.575 and 2.687(4) Å. The AgS3 group is almost planar. A fourth S atom is at a distance of 2.928(4) Å from Ag, the Ag–S being closely perpendicular to the AgS3 plane (Cascarano et al., 1987). The crystal structure of freieslebenite was determined by Wuensch and Nowacki in 1967. Wuensch and Nowacki determined the crystal structure of freieslebenite using three-dimensional counter data, systematic consideration of all possible arrangements permitted by the subcell-supercell relationship and the method of key shifts (Ito, 1973).

Physical properties

Cluster of twinned freieslebenite crystals on quartz matrix from Neue Hoffnung Gottes Mine, Bräunsdorf, Freiberg District, Erzgebirge, Saxony, Germany (Size: 5.6 x 4.4 x 1.9 cm)

Freieslebenite has a metallic luster and is opaque in transparency. The general colors for freieslebenite are gray, silver and white. It has a whitish gray streak with a hardness of 2.5 on the Mohs scale. It has an imperfect cleavage and an irregular fracture. The density of freieslebenite is 6.20-6.23 g/cm3.

Geologic occurrence

The occurrence of freieslebenite is commonly found in hydrothermal locations. A major finding of freieslebenite was located in the Hiendelaencina mining district in Spain (Frias, 1991). Freieslebenite can also be located in North and South America and throughout Asia and Europe. Deposits of freieslebenite can generally be located in proximity with minerals argentite, siderite, freibergite, polybasite, and aramayoite.

See also

References

Wikisource has the text of the 1911 Encyclopædia Britannica article Freieslebenite.
  1. ↑ Mindat
  2. ↑ Handbook of Mineralogy
  3. ↑ Webmineral data
  4. ↑ (Palache et al., 1944)
This article is issued from Wikipedia - version of the Saturday, October 04, 2014. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.