Euxenite
Euxenite - (Y ) is a rarely occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the orthorhombic crystal system with the chemical composition of (Y, Ca, Ce, U, Th ) ( Nb, Ta, Ti) 2O6. The values given in the parentheses of the elements yttrium, calcium, cerium, uranium and thorium and niobium, tantalum and titanium, in the formula each represent each other (substitution, Diadochie ), but are always in the same proportions to the other components of the mineral.
Euxenite - (Y) usually develops stocky prismatic crystals, but also occurs in the form radialstrahliger mineral aggregates. Its color varies between black, brownish black and greenish black and its stroke color between yellowish, reddish brown, and Perse.
Special Features
The mineral may be slightly radioactive due to small amounts of cerium, uranium and thorium. Taking into account the natural decay chains or existing decay products, the specific activity is given as 80 Bq / g (compared to natural potassium 31.2 Bq / g).
Although the inherent radioactivity of the mineral is rather weak, they still destroyed with time its crystal structure, so that it occurs mostly metamict.
Etymology and history
Was first discovered euxenite - (Y) by Baltazar Mathias Keilhau in an unnamed pegmatite formation at Jølster in the Norwegian province of Sogn og Fjordane and described in 1840 by Theodor Scheerer ( 1813-1875 ), of the mineral after the Greek word Greek εύξενος [ euxenos ] named for hospitable, because it is home to many rare ingredients.
In 1987, the mineral was named by the International Mineralogical Association (IMA ) has been adapted because of its predominant component after euxenite yttrium (Y ).
Classification
In the outdated, but partly still in use 8th edition of the mineral classification by Strunz the euxenite - (Y) belonged to the department of " oxides with molar ratio of metal: oxygen = 1: 2 ( MO2 and related compounds ) ", where he was named the " euxenite series " with the system no. IV/D.19 and the other members Calciosamarskit, Fersmit, Ishikawait, Loranskit - (Y), Písekit - (Y), Polycrase - (Y), Samarskite - (Y), Samarskite - (Yb ), Tanteuxenit - (Y), Uranopolykras, Yttrocolumbit - (Y) Yttrokrasit ( Y) and Yttrotantalit (Y ) was formed.
The valid since 2001 and used by the IMA 9th edition of the Strunz'schen Mineral classification assigns the euxenite - (Y ) is also in the department of " oxides with the molar ratio of metal: oxygen = 1: 2 and comparable " one. However, this is further divided according to the relative size of the involved cations and the crystal structure, so that the mineral according to its composition in the subsection "With large (± medium-sized ) cations; " Is to find where it is also the eponymous " chains of edge-sharing octahedra Euxenitgruppe "with the system no. And the other members constituting 4.DG.05 Fersmit, Kobeit - (Y) Loranskit - (Y) Polycrase - (Y) Tanteuxenit (Y ), and Uranopolykras Yttrokrasit ( Y).
The mainly common in English-speaking classification of minerals according to Dana assigns the euxenite - (Y) in the category of " oxides and hydroxides ," there but in the department of " Multiple Oxides with Nb, Ta and Ti " one. Here he is in the unnamed group 08:03:08 within the subdivision " Multiple Oxides with Nb, Ta and Ti and the formula A ( B2O6 ) " to find.
Education and Locations
Euxenite - (Y) is formed in a magmatic granitic and alkaline pegmatites, but may be secondarily enriched in soaps. Accompanying minerals can occur, among other aeschynite - (Y), albite, allanite, beryl, Betafit, biotite, columbite, Gadolinit, grenade, ilmenite, magnetite, microcline, monazite, muscovite, thorite, uraninite, xenotime and zircon.
As a rather rare mineral formation can euxenite - (Y) indeed be in different localities partly abundant, but overall he is not widespread. So far (as of 2013) are considered to be known around 400 localities. Apart from its type locality Jølster in Sogn og Fjordane, the mineral occurred in Norway, among others, still at Nesodden in Akershus; in several places in the municipalities Arendal, Evje og Hornnes, Iveland and Risr in Aust -Agder; at Hurum in Buskerud; for drag and Hundholmen in Nordland; at Tverrbotntind and Sel, Oppland; at various places in Østfold; at Tordal and Kragerø in Telemark; on Kvaloya in Troms; at some points Fund in Vest-Agder and at Hedrum in Vestfold. Known due to exceptional Euxenitfunde include Kragerø in Telemark and Hitterø in Vest-Agder, where euxenite crystals were up to 15 centimeters in length have been found.
In Germany you know euxenite - (Y) so far mainly from Saxony, so among other things Biesig, Königshain, Thiemendorf ( Waldhufen ) and Döbschütz in the district Görlitz, but also from the quarry " Steinerleinbach " at Roehrnbach in Lower Bavaria.
In Austria, found the mineral so far in Artolz and Gebhart in Lower Austria, at Hopffeldboden ( Hohe Tauern ) in Salzburg and in Zamser reason im Zillertal in Tyrol.
In Switzerland could euxenite - (Y) so far only for Cavloc Lake in Fornotal (Val Forno ) in the canton of Grisons, on Gridone in the Canton of Ticino and Crête de Thyon Herens Valley in the canton of Valais be found.
Other localities lie among other things in Egypt, Ethiopia, Australia, Brazil, China, Finland, France, French Guyana, Guyana, India, Italy, Japan, Kazakhstan, Kenya, Laos, Madagascar, Mozambique, Namibia, Niger, Portugal, Russia, Sweden, Slovakia, South Africa, South Korea, Swaziland, Czech Republic and the United States of America (USA).
Crystal structure
Euxenite - (Y ) crystallizes in the orthorhombic space group Pbcn ( Raumgruppen-Nr. 60) with the lattice parameters a = 14.64 Å; b = 5.55 Å and c = 5.19 Å and four formula units per unit cell.