Dumortierite

  • Al6 0.5 to 7 [ (O, OH) 3 | BO3 | (SiO4 ) 3]
  • Al6 (Al, Mg, Fe 3 , □ ) [ (O, OH) 3 | BO3 | (SiO4 ) 3]

Dumortierite is a rarely occurring mineral from the mineral class of " silicates and Germanates ". It crystallizes in the orthorhombic crystal system with the idealized composition Al6 0.5 to 7 [ (O, OH) 3 | BO3 | (SiO4 ) 3], and is therefore chemically seen an aluminum borosilicate with additional oxygen or hydroxide ions. Structurally Dumortierite is one of the island silicates.

In natural Dumortierite is often a small percentage of aluminum with magnesium (Mg) or iron ( Fe) is replaced ( substituted). In addition, this structure is not always completely occupied space ( □ ), which generally also of formula Al6 (Al, Mg, Fe3 , □ ) [ (O, OH) 3 | ( SiO4) 3 | BO3 ] is expressed.

The mineral is usually found in the form parallelfaseriger or radialstahliger crystals and aggregates of blue, greenish blue, violet or red-violet to brown violet color with white stroke color. Visible crystal faces have a glass-like shine, in coarse aggregate forms Dumortierite other hand, is dull.

The well-known natural stone places Azul Do Macaubas contains about 15 % Dumortierite, what is the reason for the strong blue color of the stone.

Special Features

Through strong glow Dumortierite goes into the mineral mullite under release of water (H2O) and boric oxide (B2O3 ).

Etymology and history

Dumortierite was first discovered in the quarry " Ducarre " in the community Chaponost in the Rhône region of France and described in 1881 named by MF Gonnard, of the minerals by the French paleontologist Eugene Dumortier ( 1801-1876 ).

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Dumortierite belonged to the department of " island silicates with tetrahedral foreign anions ( Neso - Subsilikate ) " where he along with Grandidierit the " Dumortierite - Grandidierit group " with the system No. Formed VIII/B.31 and the other members Boralsilit, Harkerit, Holtit, Kornerupine, Magnesiodumortierit, Ominelit, Prismatin and Werdingit.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the Dumortierite in the department of " island silicates ( nesosilicates ) ". However, this is further subdivided according to the possible presence of other anions and the coordination number of the cations involved, so that the mineral according to its composition in the subsection " island silicates with BO3 triangles and / or B, Be tetrahedra eckenteilend with SiO4 " can be found where it forms the unnamed group 9.AJ.10 together with Holtit and Magnesiodumortierit.

The mainly common in English-speaking classification of minerals according to Dana assigns the Dumortierite in the class of " silicates and Germanates " and then in the same department and sub-department of the " island silicates: borosilicates and some Beryllosilikate with (BO3 ) " a. Here he is as the namesake of the " Dumortieritgruppe " with the system no. 54.01.02 and to find the only other member Magnesiodumortierit.

Education and Locations

Dumortierite forms in aluminum-rich, regionally metamorphosed granitic pegmatites, migmatites and gneisses. Accompanying minerals occur among others andalusite, cordierite, kyanite, muscovite, quartz, rutile, sillimanite, scapolite, topaz and tourmaline.

As a rather rare mineral formation Dumortierite 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 200 localities. Apart from its type locality, the quarry " Ducarre " was the mineral in France or also belong to Rhône department town of Saint -Laurent -de- Chamousset and in Rouquié (municipality Lamontélarié ) in the Tarn department be found.

In Germany Dumortierite occurred among others Egerten in Baden -Württemberg, Drachselsried and maple mountain in Bavaria, Rockeskyll (Eifel ) in Rhineland -Palatinate and in the Council quarry near Hartmann village ( near Chemnitz ) and Waldheim in Saxony.

In Austria, the mineral has been able at Arlinggraben at Kötsch ( Wolfsberg ) on Ladinger Spitz and in Bad St. Leonhard in the Lavant valley in the Kärntener Saualpe; be found at Amstall in Lower Austria, and at Kupper reason at Easter joke on Wild Bachgraben and Swan mountain in Styria at Meidling (municipality Paudorf ) on Unterkienstock near Rossatz - Arnsdorf and on Zwettlerstrasse passing near Felling (municipality Gföhl ) Ebersdorf (municipality bodying forth ) and.

In Switzerland, you know Dumortierite Currently only the Fornogletscher in canton Graubünden, from the Pontetal and Crodolotal near Brissago and from Castione TI in the canton of Ticino.

Other localities lie among other things in Antarctica, Australia, Austria, Bolivia, Botswana, Brazil, Bulgaria, Chile, Finland, India, Italy, Japan, Canada, Madagascar, Mozambique, Namibia, New Zealand, Norway, Peru, Poland, Russia, Sweden, Switzerland, Slovakia, South Africa, South Korea, Czech Republic, Ukraine, the United Kingdom ( England) and the United States of America ( Alaska, Arizona, California, Main, Montana, Nevada, New Mexico, New York, North Carolina, Pennsylvania, Utah, Washington).

Crystal structure

Dumortierite crystallizes in the orthorhombic space group Pmcn ( Raumgruppen-Nr. 62) with the lattice parameters a = 11.83 Å; b = 20.24 Å and c = 4.70 Å and four formula units per unit cell.

Use

As a gemstone

Much like sodalite and lapis lazuli also Dumortierite is predominantly used as a gemstone. This cabochon and other smooth cuts and different for crystals Faceted surface are preferred for dense aggregate forms. In addition, aggregate forms are also processed into various arts and crafts items such as animal sculptures.

Because of its color similarity with sodalite and lapis lazuli, as well as in crystal form with Azurite, Blue Quartz is a certain confusion with these minerals. Blue Quartz with inclusions of Dumortierite is precisely referred to as Dumortieritquarz or Dumortierite quartz.

The raw material

Occasionally Dumortierite is used as raw material for ceramic insulators and laboratory equipment.

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