Franckeite

Franckeit is a rarely occurring mineral from the mineral class of sulfides and sulfosalts. It crystallizes in the triclinic crystal system with the chemical composition of (Pb, Sn) 6- 8FeSb2Sn2S14 -16 and mostly developed rosette layered aggregates, as well as thin, tabular or curved crystals in a gray-black color.

Etymology and history

Its name comes by the brothers Johann Heinrich Karl Francke (1832-1907) and Ernst Otto Francke (1838-1913), the " Chocaya Mine" in the municipality of Atocha (Bolivia ) were employed as mining engineers and partner of and brought it to Germany 1877. 1893 the mineral was first described scientifically by Prof. Alfred Stelzner in Freiberg.

Classification

In the now outdated nomenclature of minerals according to Strunz ( 8th edition ) of the Franckeit belongs to the department of " sulfides with the molar ratio of metal: sulfur, selenium, tellurium = 1: 1".

Since the revision of the Stunz'schen Mineral classification in its 9th edition, this department is subdivided into more specific structural model and the elements contained in the composition, chemical. The mineral is now appropriately in the department " sulfosalts with SnS as a model " and there in the Subsection " F. With SnS and PbS archetype structural units, "where he is the unnamed group 2.HF.25 together with Abramovit, Coirait, Researcher and Lévyclaudit.

The classification of minerals according to Dana assigns the Franckeit in the Department of sulfosalts with the ratio z / y > 4 and the ( general ) composition (A ) i ( A2 ) j [ Bycz ], where A = metals, B = semi-metals and C = non-metals sector. Together with Abramovit, Coirait, Researcher, Incait and Potosíit it forms there the Kylindritgruppe.

Modifications and varieties

There are two known varieties of Franckeits. The tin - rich Incait was until 2007 as a separate mineral and was found for the first time in 1973 in Poopó in Bolivia. Also, the tin - poor Potosíit, which was also found for the first time in 1980 in Andacaba in Bolivia, was until 1997 as an independent mineral.

Education and Locations

Franckeit formed hydrothermally especially in silver and tin deposits. It is accompanied by cassiterite, the Franckeit similar cylindrite, wurtzite, Zinkenite and others.

Worldwide, Franckeit so far (as of 2010) are detected at approximately 40 sites. Apart from its type locality Chocaya mine the mineral in the department of Potosí still in the " Carguaicollo Mine" Province Antonio Quijarro, the " Descubridora Mine" Chayanta province in which " Andacaba " deposit province José María Linares, " Cerro de Potosí ", " Siglo was XX " Rafael Bustillo Province, " Animas Mine " Municipio Atocha, " Asunta Mine " and" Vetillas Mine " in the district of San Vicente, " Santa Isabel Mine " Sur province Lípez and in Cochabamba Department and the Oruro Department.

Other localities include Jujuy in Argentina, New South Wales in Australia, Cochabamba Department, Departamento Oruro and Potosí Department in Bolivia, Guangxi in the People's Republic of China, Auvergne and Brittany in France, Western Thrace in Greece, and California in the United States.

Crystal structure

Franckeit triclinic in two defined sub-cell with the lattice parameters

• Pseudotetragonal: a = 17.2 Å; b = 5.79 Å; c = 5.82 Å; α = 91.4 °; β = 95.5 ° and γ = 88.2 °
• Pseudohexagonal: a = 17.2 Å; b = 3.65 Å; c = 6.3 Å; α = 91.3 °; β = 96.2 ° and γ = 88.6 °

Use

Franckeit has a tin content of about 13.68 % and is used as tin ore for local use accumulation.