Ottrelite

• Salmit

Ottrélith is a rarely occurring mineral from the mineral class of " silicates and Germanates ". It crystallizes in the monoclinic crystal system with the idealized chemical composition of Mn 2 Al 2 [O | (OH ) 2 | SiO 4 ], so it is a manganese -aluminum silicate with additional oxygen and hydroxide ions. Structurally Ottrélith is one of the island silicates ( nesosilicates ).

Since naturally formed Ottrélithen some of the manganese replaced by iron and / or magnesium ( substituted ) may be, the formula is also occasionally with ( Mn2 , Fe2 , Mg) Al2 specified, the [O | SiO 4 | (OH ) 2] in the parentheses specified items may indeed represent each other in the formula, but are always in the same proportions to the other components of the mineral.

Ottrélith is translucent and develops rarely well-trained, hexagonal tabular crystals to about four millimeters size. He usually can be found in the form of irregular grains or grain aggregates of greenish to dark gray color, which is sometimes described as pistachio green. His stroke color is greenish gray. Uninjured crystal faces show a glass-like shine. On cleavage planes but it could be almost similar to diamond.

Etymology and history

Ottrélith was first discovered in the area of Ottré near the village of Durbuy in the Belgian province of Luxembourg. The mineral was first described in 1818 by Laurent -François Dethier 1842 and again by Alfred Des Cloizeaux and Augustin Alexis Damour.

The mineral was named after its type locality.

Classification

Already in the outdated, but partly still in use 8th edition of the mineral classification by Strunz was one of Ottrélith to the mineral class of " silicates and Germanates " and then to the Department of " island silicates with tetrahedral foreign anions ( Neso - Subsilikate ) ", where he, together with chloritoid and Magnesiochloritoid the " Chloritoidgruppe " with the system number. VIII/B.24 formed.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the Ottrélith also in the department of " island silicates ( nesosilicates ) ". This is in addition to the possible presence of additional anions, however, are further subdivided by the coordination of the cations involved, so that the mineral according to its composition in the subsection " island silicates with additional anions; Cations iner, he " is to find where it also together with chloritoid and Magnesiochloritoid the " and / or nurer coordination Chloritoidgruppe "with the system no. 9.AF.85 forms.

The mainly common in English-speaking classification of minerals according to Dana assigns the Ottrélith in the class of " silicates and Germanates " and then in the Department of: an " island silicates SiO4 Groups and O, OH, F, and H2O". Here he is with chloritoid, Magnesiochloritoid and Carboirit in the " Chloritoidgruppe " with the system no. ": With cations SiO4 Groups and O, OH, F, and H2O only in coordination island silicates " to find 52.03.03 within the subdivision.

Education and Locations

Ottrélith forms in passages and cavities of low to moderate, metamorphic rocks, but can also be precipitated from moderate hydrothermal solutions. Accompanying minerals, among others andalusite, various chlorites, Davreuxit, dickite, kaolinite, pyrophyllite, quartz and rutile may occur.

A rare mineral formation Ottrélith could be detected only in a few localities, where so far (as of 2014) are about 60 localities known as. Apart from its type locality Ottré the mineral occurred in Belgium nor in animals of Carrière and Bihain (municipality Vielsalm) in Stavelot Massif and in the quarry " Sur les Roches " at Bastogne in the province of Luxembourg and at Rahier (municipality Stavelot ) in the Province of Liege on.

In Germany Ottrélith found so far only in a metamorphic rock zone at Wippra and Sengelbachtal at Biesenrode in Saxony -Anhalt and in Chemnitz- Rabenstein in Saxony.

Other previously known localities include the " La Pierre Plantée " Pass near Mas Aubert in the French department of Gard, the quarry Tignai in the northern Italian municipality of Bussoleno; Fund some points in the Abitibi- Témiscamingue communities and Les Appalaches in the Canadian province of Quebec; "La Hueca Mine" ( Sapo Negro) at Coalcomán de Vázquez Pallares in the Mexican state of Michoacán; Nyberget (municipality Smedjebacken ) in Dalarna, the Västanå iron mine near Näsum (municipality Bromölla ) and Vånga ( Kristianstad municipality ) in Skåne and Ransäter (municipality Munkfors ) in Värmland in Sweden as well as several places in various states across the United States.

Crystal structure

Ottrélith crystallizes in the monoclinic space group Cc or C2 / c ( Raumgruppen-Nr. 9 or 15) with the lattice parameters a = 9.50 Å; b = 5.48 Å; c = 18.21 Å and β = 101.8 ° and 8 formula units per unit cell.