Polybasite
- Polybasit - T2ac
Polybasit ( Polybasit - T2ac (from 09 /2006), Eugen gloss, Sprödglaserz ) is a mineral from the mineral class of sulfides and sulfosalts and belongs to the family of the silver-rich sulfosalts with an excess of small, monovalent cations (Ag, Cu) relative to As, Sb, Bi is the simplified structural formula
The copper - silver ratio is variable and the silver contents are around 64-72 %. In addition, low levels of iron and zinc and antimony and selenium occur.
Polybasit part with the isotypic minerals Pearceit (more As than Sb) and Selenopolybasit (more Se than S ) to a solid solution series ( Polybasitreihe ).
Polybasit crystallizes in rhombic plates or found coarse and finely dispersed in the surrounding minerals. It is iron- black with metallic luster and red translucent in very thin flakes. 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 derives from the Greek Polybasit πολὺ poly for " many" and βάσις basis for " levels " that, due to the crystal structure.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz Polybasit belonged to the mineral class of " sulfides and sulfosalts " and then to the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 independent group II/E.05 formed.
The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the Polybasit also in the class of " sulfides and sulfosalts ," there, however, in the newly defined division of " Sulfoarsenide, Sulfoantimonide, Sulfobismuthide " a. This department is also further divided according to the crystal structure and the possible presence of additional sulfur, so that the mineral is according to its structure and composition in the subdivision of " island ( Neso ) Sulfarsenide etc., with additional sulfur ( S) " to find where it together with Cupropearceit, Cupropolybasit, Pearceit -Tac (formerly Pearceit ) Pearceit - T2ac (formerly Arsenpolybasit ) Pearceit - M2a2b2c (formerly Arsenpolybasit ) Polybasit -Tac (formerly Antimonpearceit ) Polybasit - T2ac (formerly Polybasit ) Polybasit - M2a2b2c (formerly Polybasit ) and Selenopolybasit the " Pearceit - Polybasit group " with the system no. 2.GB.15 forms.
The mainly common in English-speaking classification of minerals according to Dana assigns the Polybasit or the Polybasit - M2a2b2c in the class of " sulfides and sulfosalts " and there in the department of " thio " one. Here he is with Pearceit - T2ac in the " Polybasitgruppe " with the system no. 03:01:07 to find within the subdivision of the " sulpho with the ratio z / y > 4 and the composition (A ) i ( A2 ) j [ Bycz ], A = metals, semimetals B =, C = non-metals ".
Education and Locations
Polybasit found on hydrothermal Silbererzgängen that were formed at low to medium temperatures, eg, at Freiberg, St. Andrew Berg, Jáchymov ( Joachimsthal ) Schemnitz in Slovakia, Mexico, Nevada, Idaho. It occurs together with Pyragyrit ( Ag3Sb3S3 ), tetrahedrite ( Cu12Sb4S13 ) stephanite, further Silbersulfosalzen, acanthite, gold, quartz, calcite, dolomite and barite.
Crystal structure
The Polybasitstruktur builds up from two different layered units with the compositions [ Ag9CuS4 ] 2 and [ (Ag, Cu ) 6 ( Sb, As) 2S7 ] 2 - on. These multilayers are stacked alternately along the c -axis.
Polybasit ( and Pearceit ) crystallizes both trigonal and monoclinic in three polytypic 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 mainly due to the ordered distribution of the silver (Ag ) to the various lattice positions.
Use
Polybasit is locally an important silver ore.