Sodalite

Sodalite is a local accumulation at While abundant, but overall rather little spread mineral from the mineral class of " silicates and Germanates ". It crystallizes in the cubic crystal system with the chemical composition Na8 [ Cl2 | ( AlSiO4 ) 6] and usually develops granular to massive aggregates of a size of up to about one meter, rare small, millimeter - to centimeter-sized crystals in mostly gray-blue to dark blue color. Depending on the foreign admixtures or sodalite inclusions can also be white, yellow or purple be colored to pink ( Hackmannit ). Even colorless crystals are known.

Sodalite is one of the Foiden and together with Bicchulith, Danalith, Genthelvin, Haüyn, Helvin, Kamaishilith, Lazurite, nosean, tsaregorodtsevite and Tugtupite a group of minerals named after him.

Special Features

Depending on the locality has sodalite under long-wave and short-wave UV light has a strong orange-red fluorescence and phosphorescence on yellow.

Sodalite is readily soluble in weak to moderately strong acids such as hydrochloric acid, which is initially discolored and dissolves after some time, with precipitation of silica gel. Under the action of heat, the reactions, especially the loss of color even faster. Already boiling water is in a position to withdraw the sodalite sodium and chlorine.

Etymology and history

The name sodalite composite loan word from the Latin Sodium sodium and the Greek λίθος lithos for stone and refers to its high sodium content.

Was first found in the sodalite Ilímaussaq massif in the province Kitaa (West Greenland) and described in 1812 by Thomas Thomson.

Linus Pauling published in 1930 a first proposal for the structure of sodalite, the 1967 Jürgen Lons and H. Schulz by their crystallographic work confirmed.

Classification

In the old ( 8th edition ) and new classification of minerals ( 9th Edition ) by Strunz is associated with the tectosilicates the sodalite. The entire mineral class and its departments, however, were partially re- sorted in the new Strunz'schen Mineral classification and divided more finely. Sodalite is therefore due to its crystal chemical structure now under the "framework silicates ( tectosilicates ) with additional anions, without zeolitic H2O" to find.

The classification of minerals according to Dana assigns the sodalite likewise in the Department of framework silicates, but renames them precisely according to the crystal structure with " Al- Si lattice, feldspar and related species ". The sodalite group has opposed the Strunz'schen Systematics three members less, since the minerals Helvin, Danalith Genthelvin and form their own group.

Modifications and varieties

As Hackmanite a sulfate-containing, purple - pink variety is referred to, in Quebec (Canada) was discovered in abrasive decent quality for the first time in 1991. A special feature of Hackmanits from Sar -e -Sang is its photochromism, probably caused by color centers. In contrast to "normal colored " sodalite its color does not fade in sunlight, but is more intense. Even stronger is the effect when using a UV lamp, under whose influence the color can be increased within tenths of a second to a vivid violet. In addition, there is a pink to orange fluorescence. Hackmanite other sites, however, invite their color in the dark again.

Education and Locations

Sodalite usually forms in igneous rocks with medium to low SiO2 content such as, among others, nepheline syenites, phonolites and related rocks, but also in metasomatic calciferous stones and marble. Accompanying minerals include aegirine, ankerite, albite, andradite, barite, calcite, cancrinite, fluorite, nepheline, microcline and sanidine.

Overall, sodalite has so far (as of 2011) are detected in more than 300 localities. Apart from its type locality Ilímaussaq solid sodalite was also found in other regions of the province and the province Kitaa tunu in Greenland.

Other previously known localities (as of 2009 ) include Badakhshan ( Sar -e -Sang ) and Lugar in Afghanistan; Antarctica; Shvanidzorskii in Armenia; New South Wales and Tasmania in Australia; Cochabamba in Bolivia; the northeast and southeast regions of Brazil; Shaanxi in China; Baden- Württemberg (Kaiser chair) and Rhineland -Palatinate (Eifel ) in Germany; Auvergne and Rhône -Alpes in France; Thrace in Greece; Los Archipelago in Guinea; Puglia, Campania and Lazio in Italy; the southern region of Cameroon; British Columbia, Ontario and Quebec in Canada; in Almaty and Aktobe in Kazakhstan; Chonashu ( Irtashskii ) in Kyrgyzstan; Kivu in the Congo; Pokchin -san in Korea; in Balaka and Chitipa in Malawi; in Kidal in Mali; Meknès- Tafilalet in Morocco; Chihuahua in Mexico; in the Gobi Desert (Mongolia ); Mandalay in Myanmar; Khomas in Namibia; several regions in Norway; Burgenland and Styria in Austria; Puno in Peru; in the Azores and at Faro in Portugal; in Harghita County in Romania; some regions in Russia; South Africa; in the Canary Islands in Spain; several regions in Sweden; Ticino in Switzerland; Arusha in Tanzania; Scotland in the UK; Bohemia in the Czech Republic; Donetsk in Ukraine; several regions of the U.S.; and the Amazon in Venezuela. In Zambia, two localities in Solwezi and Lusaka.

Crystal structure

Sodalite crystallized in the cubic crystal system in the space group ( Raumgruppen-Nr. 218 ) with the lattice parameters a = 8.88 Å, and one formula unit per unit cell.

The sodalite structure (Fig. 1) can be described as a cubic close packing of 6- rings in direction. Aluminium, silicon and oxygen atoms form the covalent structure of the grating. Figure 2 shows the positions of the Al and Si. Between the Al and Si near the red lines connecting each one O. The grid carries a negative charge and is an ionic bond with sodium cations. (see aluminosilicate ) This structure requires the chemical composition Na6 [ Al6Si6O24 ] and is colorless. Each sodalite cage of this composition has an empty interior space and may contain other substances ( cations and anions or water). These materials may be the cause of the colors of the based on the sodalite minerals.

Related Minerals

• Lazurite (also ultramarine ) is a component of the mineral mixture lapis lazuli. Sodalite with S3 - and S2 - radicals generated by the arrangement (coordination) in the sodalite cages an intense blue color.
• Nosean also has the skeletal structure of sodalite, but only every second cage with the divalent sulfate anion is busy. The compound is colorless.

Use

Sodalite is due to the often lively spotted coloration like processed into semi-precious stones in the form of cameos and small sculptures, but also beads or cabochons for necklaces and rings. Large deep blue stones are sometimes referred to as the " Royal Blue " blue stones as " Blue Sapo " blue stones with a few bright inclusions as " Blue Tiger " and light blue stones with white inclusions as " Nuvolato ".

When decorating sodalite is also used in the aquarium hobby.

Large deposits such as, among others, in Bolivia, Brazil, Zambia and Namibia are processed into floor and wall tiles and cladding panels. Where the Namibian occurrence is not currently being terminated. Bolivian material is very rarely available in the market because of the degradation takes place under difficult conditions. Blue King of Zambia is also not degraded because as decorative rock not visually attractive. Introduced in the market is only the Brazilian material, trade name Azul Bahia.

As the pigment sodalite is of subordinate importance. His him related mineral Lazurite and the mineral lapis lazuli mixture are preferred as a pigment supplier.

In science serve synthetic sodalites whose composition is often different from that of the mineral, as a model system for the substance group zeolites. The sodalith cage is a structural component of compounds with important zeolite A, zeolite X and zeolite Y. The technical synthesis of the sodalites is usually hydrothermally.