Riebeckite

The mineral riebeckite is a rarely occurring chain silicate from the group of alkali amphiboles. It crystallizes in the monoclinic crystal system with the composition □ Na2Fe2 3 Fe3 2 [( OH) 2 | Si8O22 ], and is therefore in chemical terms, a complex composed of sodium iron silicate, wherein the structural place of sodium ( symbolized by □ ) is not fully occupied.

Riebeckite developed rarely long, prismatic crystals, but can then be up to 20 cm long. In general, it can be found in the form feinnadeliger to fibrous mineral aggregates, which are referred to as crocidolite. The translucent to opaque mineral is usually from black to dark blue, also in thin layers of dark blue to yellow- green color. On the dash panel leaves Riebeckite a blue-gray line. Visible crystal faces have a glass-like luster, whereas fibrous varieties shimmer like silk.

With Magnesioriebeckite □ Na2 (Mg, Fe) 3Fe3 2 [( OH) 2 | Si8O22 ] riebeckite forms a complete solid solution series.

Etymology and history

Was first discovered by the German ethnologist Riebeckite, mineralogist and naturalist Emil Riebeck (1853-1885) in the Socotra archipelago ( Socotra ) in Yemen and described in 1888 by Adolf Sauerland, who named the mineral after its discoverer.

Classification

Already in the now outdated but still in use 8th edition of the mineral classification by Strunz was one of Riebeckite the mineral class of " silicates and Germanates " and then to the Department of " chain silicates and phyllosilicates ( inosilicates ) " where he along with Arfvedsonite, crossite, Dellaventurait, Eckermannit, Ferrinybøit, ferric Ferronybøit, Ferripedrizit, Ferriwhittackerit, Ferro - Eckermannit, Ferroleakeit, Ferroglaukophan, fluoro- Ferroleakeit, fluoro - magnesio - Arfvedsonite, Fluoronybøit, glaucophane, Kaliumarfvedsonit, Kaliumleakeit, Kornit, Kozulith, Leakeit, magnesio - Arfvedsonite, Magnesioriebeckite, sodium ferric Ferropedrizit, sodium Ferripedrizit, Nybøit, Obertiit and Ungarettiit the independent " amphibole group, subgroup alkali amphiboles " with the system no. VIII/F.08 formed.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the Riebeckite also in the class of " silicates and Germanates " and there in the department of " chains and chain silicates ( inosilicates ) " one. This division, however, is further subdivided according to the type of chain or belt structure and partly by membership of particular mineral affinities, so that the mineral is found according to its composition in the subsection " Klinoamphibole " where there along with Arfvedsonite, Dellaventurait, Eckermannit, ferric Ferronybøit, ferric Klinoferroholmquistit, Ferrinybøit, ferric Ottoliniit, Ferriwhittakerit, Ferro - Eckermannit, Ferroglaukophan, Ferroleakeit, Ferronybøit, Ferropedrizit, fluorine Arfvedsonite, fluoro- Ferroleakeit, fluoro- potassium magnesio - Arfvedsoni, fluoro - magnesio - Arfvedsonite, fluoro- Natriumpedrizit, Fluoronybøit, fluorine - riebeckite, glaucophane, Klinoferroholmquistit, Kornit, Kôzulith, Leakeit, magnesio - Arfvedsonite, Magnesioriebeckite, Nybøit, Obertiit, Ottoliniit, Pedrizit, potassium magnesio - Arfvedsonite, Kaliumarfvedsonit, Kaliumleakeit, sodium ferric Klinoferroholmquistit, sodium ferric Ferropedrizit, sodium Ferripedrizit, sodium Ferropedrizit, Natriumpedrizit, Ungarettiit and Whittakerit the " alkali - Klinoamphibole, glaucophane Eckermannit group " with the system no. 9.DE.25 forms.

The mainly common in English-speaking classification of minerals according to Dana assigns to the category of " silicates and Germanates " there, however, in the fine already divided the department " chain silicates: Double unbranched chains, W = 2". Here he is the only member / together with the " Group 4, sodium amphiboles " with the system no. 66.01.03c within the sub-division of " chain silicates: Double unbranched chains, W = 2 amphibole configuration " to find.

Modifications and varieties

The only variety is known at crocidolite (also hornblende asbestos or blue asbestos ).

Education and Locations

Riebeckite forms either magmatic granite, rhyolite and syenite, where it is usually found in paragenesis with aegirine, nepheline, albite or Arfvedsonite, or with tremolite and ferro - actinolite associated in metamorphic rocks as quartzite or iron-rich shales. Other accompanying minerals include grunerite, magnetite, hematite, stilpnomelane, ankerite, siderite, calcite.

Weathering by oxidation and partial replacement of Riebeckits by silica ( silicification ) is the mineral with time initially in the variety Hawkeye and finally to the variety tiger eye.

As a rather rare mineral formation Riebeckite can be abundant in part to different sites, overall it is not very common. So far (as of 2011) are considered to be known around 300 localities.

Known due to extraordinary finds of riebeckite, among other Khangay in Mongolia, where crystals to about 15 cm in length were revealed. In the United States there is the Great Blue Hill a mountain that was named after the bluish sheen of his granite rock that contains riebeckite.

The only known locality in Austria is the Schlossberg at Gloggnitz in the industrial district of Lower Austria. In Switzerland, Riebeckite found on Glärnisch in the canton of Glarus, at Piz Lunghin, Plaun Grand ( near Sils im Engadin / Segl ) and Kistenpass in the canton of Graubünden and Uri on the ground and in Ängisort (near Seedorf UR) in the canton of Uri.

Other localities lie among others in Algeria, Antarctic, Argentina, Australia, Bolivia, Brazil, China, France, Greenland, India, Israel, Italy, Jamaica, Japan, Yemen, Canada, Kazakhstan, Kenya, Kyrgyzstan, Madagascar, Malawi, Mongolia, Namibia, New Zealand, Niger, Nigeria, North Korea, Norway, Pakistan, Portugal, Reunion, Russia, Saudi Arabia, Sweden, Zimbabwe, Slovakia, Spain, South Africa, Tajikistan, Ukraine, Venezuela, the United Kingdom (Great Britain, inter alia Ailsa Craig ) and the United States (U.S.).

Crystal structure

Riebeckite crystallizes in the monoclinic space group C2 / m ( Raumgruppen-Nr. 12) with the lattice parameters a = 9.81 Å; b = 18.01 Å; c = 5.33 Å and 103.7 ° and β = 2 formula units per unit cell.

Use

Of industrial importance as " asbestos " was mainly the fibrous variety crocidolite, since it can be readily spun and like the other forms of asbestos is heat-and acid-resistant. Due to the strong health hazards caused by the fine asbestos fibers, but also crocidolite asbestos is now no longer used.