Arfvedsonite

  • Arfwedsonit

Arfvedsonite (also Arfwedsonit ) is a rarely occurring mineral from the mineral class of " silicates and Germanates ". It crystallizes in the monoclinic crystal system with the composition NaNa2 ( Fe2 ) 4Fe3 [( OH) 2 | Si8O22 ], and is therefore chemically seen a sodium iron silicate, which structurally to the double chain silicates and to the group of amphiboles with the general composition A0 1B2C5T8O22 (OH ) 2, belongs. The unusually appearing twice naming of sodium at the beginning of the chemical formula of the Arfvedsonits indicates precisely this belonging, since the positions A and B are each occupied in its crystal structure of sodium.

Arfvedsonite is translucent to opaque and developed mostly tabular to prismatic, striped crystals of up to 60 centimeters in length with glass-like sheen on the surfaces. Occasionally, it is also found in the form radialstrahliger, fibrous mineral aggregates. The mineral occurs only in dark blue to black in color before, with thin edges may also appear dark green. His stroke color varies from dark bluish gray and gray-green.

With a Mohs hardness 5-6 Arfvedsonite belongs to the medium-hard minerals that can be (5) and orthoclase (6 ) scratch with a good pocket knife or a steel file similar to the reference minerals apatite.

Arfvedsonite forms a solid solution series with magnesio - Arfvedsonite ( NaNa2 (Mg, Fe) 4Fe3 [( OH) 2 | Si8O22 ] ).

Special Features

Due to its similarity in color and hardness Arfvedsonite can be confused with aegirine and augite. However, aegirine, unlike the Arfvedsonite a light yellow gray line and augite has a stronger birefringence with optically positive character ( Arfvedsonite optically negative).

Before the blowpipe Arfvedsonite melts very easily with a yellow flame coloration and form a magnetic bead.

Etymology and history

Was first discovered in the Arfvedsonite Ilímaussaq intrusion of Kangerdluarssuq Fjord in southwest Greenland and described in 1823 by Henry James Brooke ( 1771-1857 ), who named the mineral after the Swedish chemist Johan August Arfwedson.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Arfvedsonite belonged to the general ward of the " chain silicates and phyllosilicates ( inosilicates ) " where he along with Dellaventurait, Eckermannit, Ferrinybøit, ferric Ottoliniit, Ferriwhittackerit, Ferro - Eckermannit, Ferroglaukophan, Ferroleakeit, fluoro- Ferroleakeit, fluoro- potassium magnesio - Arfvedsonite, fluoro - magnesio - Arfvedsonite, fluoro- Natriumpedrizit, Fluoronybøit, glaucophane, Kaliumarfvedsonit, Kaliumleakeit, Kornit, Kôzulith, Leakeit, magnesio - Arfvedsonite, Magnesioriebeckite, sodium Ferripedrizit, sodium ferric Ferropedrizit, Nybøit, Obertiit, riebeckite, Ungarettiit the subgroup of " alkali amphiboles " with the system no. VIII/F.08 formed within the amphibole group.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the Arfvedsonite also included in the department's " chain and chain silicates ( inosilicates ) ". However, this is further subdivided according to the type of chain formation and / or membership of larger mineral families, so that the mineral according to its construction in the subsection " Klinoamphibole " and then in the group of " alkali Klinoamphibole, glaucophane Eckermannit group " with system no. Is to find 9.DE.25.

The mainly common in English-speaking classification of minerals according to Dana assigns the Arfvedsonite in the class of " silicates and Germanates " and there in the department of " chain silicates: Double unbranched chains, W = 2". Here he is in Group 4, sodium amphiboles within the subdivision " chain silicates: Double unbranched chains, W = 2 amphibole configuration " to find.

Modifications and varieties

As Juddit a manganese-containing variety of Arfvedsonite is called. Juddit 1908 was named by Lewis Leigh Fermor in honor of the British geoscientist John Wesley Judd.

Education and Locations

Arfvedsonite is next to aegirine and Aegirinaugit a typical mineral in igneous rocks such as granite bright alkaline and pegmatite. He rarely formed by regional metamorphism. Accompanying minerals occur side Aegirin on, you still albite, Katophorit, Magnesiokatophorit, nepheline, quartz and riebeckite.

As a rather rare mineral formation Arfvedsonite can indeed be abundant in part to different sites, overall it is not very common. So far (as of 2013) are considered to be known around 270 localities. Apart from its type locality Ilímaussaq / Kangerdluarssuq where the mineral was found in many places, Arfvedsonite yet entered into Greenland at Ivittuut and Narsaarsuk in West Greenland and East Greenland Kangerlussuaq.

In Germany Arfvedsonite was previously on cat's back in the Odenwald (Baden- Württemberg), on Gabbrosteinbruch (Bear quarry ) near Bad Harzburg ( Lower Saxony) and in the pit " brothers unity " at Bösenbrunn in the Saxon Vogtland be found.

Other localities lie among others in Algeria, Antarctica, Argentina, Armenia, Australia, Brazil, Chile, China, the Democratic Republic of Congo, France and French Polynesia, Greece, Guinea, Guyana, India, Italy, Japan, Cameroon, Canada, on the Channel Island of jersey, Kazakhstan, Kenya, Korea, Libya, Madagascar, Malawi, Morocco, Macedonia, Mongolia, Namibia, New Zealand, Niger, Nigeria, Norway, Portugal, Réunion, Romania, Russia, on St. Helena, in Saudi Arabia, Spain, Sweden, South Africa, Tajikistan, Czech Republic, Uganda, Ukraine, Hungary, Uruguay, the United Kingdom ( UK) and the United States of America (USA).

Crystal structure

Arfvedsonite crystallizes in the monoclinic space group C2 / m ( Raumgruppen-Nr. 12) with the lattice parameters a = 10.01 Å; b = 18.08 Å; c = 5.33 Å and 104.1 ° and β = 2 formula units per unit cell.

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