Piemontite

Piemontite (also piemontite or manganese epidote ) is a rarely occurring mineral from the mineral class of " silicate and germanate ". It crystallizes in monoklinenen crystal system with the chemical composition Ca 2 ( Mn 3 , Fe) (Al, Mn3 ) 2 [O | OH | SiO4 | Si2O7 ] and most developed prismatic crystals, but also radial- to -grained aggregates in yellow-red to crimson, reddish brown or black violet color.

Etymology and history

Was first found in 1853 in piemontite Saint-Marcel/Piemont in Italy and described by Gustav Adolf Kenngott, who named the mineral after its type locality.

Classification

In the now outdated nomenclature of minerals by Strunz ( 8th edition ) of the piemontite still belongs to the general ward of the "Group silicates ( Sorosilikate ) ", where he is a member of the large group of epidote.

Since the revision of the Strunz'schen Mineral classification in its 9th edition, this department is precisely divided according to the type of silicate complexes occurring in the compound and the coordination of the cations involved. The piemontite is accordingly in the subdivision of " group silicates with mixed SiO4 and Si2O7 groups; Cations in oktahedraler and greater coordination " and there is still a member of the Epidotgruppe.

The commonly used in English-speaking classification of minerals according to Dana assigns the piemontite also in the Department of the silicates group, however, there in the subdivision of " group silicates with insular, mixed, individual and larger groups with cations in tetrahedral and higher coordination; Single and double groups (n = 1,2). " Again, he is a member of Epidotgruppe, specifically the " epidote - subgroup ".

Education and Locations

Piemontite formed predominantly in slate, amphibolite - facies or other metamorphic rocks. Occasionally it is also found in igneous rocks such as rhyolites and pegmatites. Accompanying minerals include calcite, epidote, glaucophane, orthoclase, quartz, and tremolite.

Globally, could the mineral (as of 2010) are detected at around 200 localities. Apart from its type locality Piedmont it was to be found in Italy or in the regions of Aosta, Liguria, Lombardy and Tuscany.

Other localities are the Antarctica; the Chinese provinces of Qinghai and Sichuan; the Región de Coquimbo in Chile; Bavaria, Hesse and Schleswig -Holstein in Germany; Languedoc -Roussillon and Midi- Pyrénées in France; Greece; India; Hokkaido, Honshu, Kyushu and Shikoku in Japan; British Columbia and Quebec in Canada; Morocco; Macedonia; on the South Island of New Zealand; Oppland, Rogaland, Sogn og Fjordane, Sør- Trøndelag and Telemark in Norway; Salzburg and Tyrol in Austria; in the eastern and western regions of Siberia, North-West Russia and the Urals in Russia; several regions of Sweden; the cantons of Graubünden, Ticino and Valais in Switzerland; Serbia; Spain; Limpopo and Northern Cape in South Africa; Tanzania; Turkey; Wales in the United Kingdom ( UK), and in several regions of the United States of America (USA).

Crystal structure

Piemontite crystallizes in the monoclinic space group P21 / m with lattice parameters a = 8.89 Å; b = 5.68 Å; c = 10.20 Å and β = 115.2 ° and two formula units per unit cell.

Use

Piemontite has except as a mineral specimen minimal economic importance. It is sometimes made ​​into gemstones, but there is a likelihood of confusion with the red zoisite variety Thulit. Among other things, consist Thulite from Norway rarely pure Thulit but almost always consists of a mixture of Thulit, piemontite, quartz, muscovite mica, tremolite and calcite. Often the Piemontite are so heavily interspersed with quartz, that they would be referred to as " piemontite Quartz ". In piemontite - muscovite - quartz with a significant content of muscovite mica is produced similar to the oligoclase - variety " sun stone ", aventurine quartz or synthetic Goldfluss a conspicuous " glitter effect ". In the trade, this stone is accordingly often offered as a so-called " red aventurine quartz ".