Polybasite

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Polybasite
Polybasite-37890.jpg
Polybasite from the Husky Mine, Elsa, Galena Hill, Mayo Mining District, Yukon, Canada
Size: 2.2 × 1.8 × 0.4 cm
General and classification
other names

Polybasite T2ac

chemical formula (Ag, Cu) 16 Sb 2 S 11
Mineral class
(and possibly department) 		Sulfides and sulfosalts
System no. to Strunz
and to Dana 		2.GB.15 ( 8th edition : II / E.05)
03.01.07.02
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol Please complete!
Frequent crystal faces {001}
Twinning after {110}
Physical Properties
Mohs hardness 2 to 2.5
Density (g / cm 3 ) 6 to 6.25
Cleavage indistinct after {001}
Break ; Tenacity uneven
colour black
Line color reddish black
transparency opaque, dark red translucent
shine shiny metal
Crystal optics
Refractive index n  = 2.72
Optical character biaxial negative
Pleochroism weak

Polybasit (Polybasit-T2ac (from 09/2006), Eugenglanz, Brödglaserz) is a mineral from the mineral class of sulfides and sulfosalts and belongs to the family of silver-rich sulfosalts with an excess of small, monovalent cations (Ag, Cu) in relation to As, Sb, Bi. The simplified structural formula is

[Ag 9 CuS 4 ] [(Ag, Cu) 6 (Sb, As) 2 S 7 ] with more than 1 Sb per formula unit.

The copper-silver ratio is variable and the silver content is 64-72%. In addition, there are low levels of iron and zinc as well as antimony and selenium.

Polybasite belongs to a mixed crystal series (polybasite series) with the isotypic minerals Pearceit (more As than Sb) and Selenopolybasite (more Se than S).

Polybasite crystallizes in rhombic tablets or is found coarse and finely distributed in the surrounding minerals. It is iron black with a metallic sheen and translucent red in very thin leaflets. It has a Mohs hardness of 2 to 2.5 and a density of 6 to 6.25 g / cm³.

Etymology and history

The name polybasite derives from the Greek πολὺ poly for “many” and βάσις basis for “levels”, which is due to the crystal structure.

Gustav Rose (1798–1873) and August Breithaupt (1791–1873) discovered the mineral independently of one another in 1829. Breithaupt called it Eugenglanz, Rose gave it the name Polybasite. Justus von Liebig writes in his “Annalen der Chemie” about the discovery of polybasite: “Polybasite was first distinguished from brittle glass ores by G. Rose as a special mineral . A new series of analyzes of this mineral has been undertaken by H. Rose . "

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz Polybasit belonged to the mineral class of "sulfides and sulfosalts" and then to the Department of "thio" where he along with Billingsleyit , Cupropearceit , Pearceit , Antimonpearceit , Arsenpolybasit and Selenopolybasit the independent group II / E.05 formed.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns the polybasite to the class of “sulfides and sulfosalts”, but in the newly defined section of “sulfarsenides, sulfantimonides, sulfbismutides” " a. This is further subdivided according to the crystal structure and the possible presence of additional sulfur , so that the mineral according to its structure and composition can be found in the subdivision of "Island sulfarsenides (Neso sulfarsenides) etc., with additional sulfur (S)" is where it is together with Cupropearceit, Cupropolybasit , Pearceit-Tac (formerly Pearceit), Pearceit-T2ac (formerly arsenic polybasite ), Pearceit-M2a2b2c (formerly arsenic polybasite ), Polybasit-Tac (formerly Antimonypearceit), Polybasit-T2ac (formerly Polybasit), Polybasit-M2a2b2c (formerly Polybasit) and Selenopolybasit the "Pearceit-Polybasit-Gruppe" with the system no. 2.GB.15 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the polybasite or the polybasite-M2a2b2c to the class of "sulfides and sulfosalts" and there in the department of "sulfosalts". Here it is together with Pearceit-T2ac in the "polybasite group" with the system no. 03.01.07 within the subdivision of " Sulphosalts with the ratio z / y> 4 and the composition (A +) i (A2 +) j [ByCz], A = metals, B = semi-metals, C = non-metals ".

Education and Locations

Polybasite is found on hydrothermal silver veins that were formed at low to medium temperatures, e.g. B. near Freiberg , Sankt Andreasberg , Jáchymov ( Joachimsthal ), Schemnitz in Slovakia , in Mexico , Nevada , Idaho . It occurs together with pyrargyrite (Ag 3 SbS 3 ), tetrahedrite (Cu 12 Sb 4 S 13 ), stephanite , other silver sulpho salts , acanthite , gold , quartz , calcite , dolomite and barite .

Crystal structure

The polybasite structure is made up of two different layered building units with the compositions [Ag 9 CuS 4 ] 2+ and [(Ag, Cu) 6 (Sb, As) 2 S 7 ] 2− . These layer packages are alternately stacked on top of one another in the direction of the c-axis.

Polybasite (and Pearceite) crystallizes both trigonal and monoclinic in three polytype structures:

  • Polybasit-Tac (old: Antimonpearceit), trigonal
  • Polybasit-T2ac (old: Polybasit-221), trigonal
  • Polybasit-M2a2b2b (old: Polybasit-222), monoclinic

The doubling of the individual unit cell axes (2a, 2b, 2c) is essentially based on the orderly distribution of the silver (Ag) on ​​the various grid positions.

use

Polybasite is an important local silver ore.

See also

Individual evidence

  1. ↑ Mineral Atlas: Polybasit-T2ac
  2. ^ Type mineral catalog Germany, University of Hamburg
  3. ↑ Justus Freiherr von Liebig: Justus Liebig's Annalen der Chemie, Volumes 13-14. Meyerschen Hof-Buchh. and the Winterschen Universitäts-Buchh, 1835, p. 91. Google Books
  4. ↑ Angew. Mineralogy: polybasite

literature

Web links

Commons : Polybasite  - collection of images, videos and audio files