Ottrelith
| Ottrelith | |
|---|---|
 |
|
| General and classification | |
| other names |
Salmit |
| chemical formula | Mn 2+ Al 2 [O | (OH) 2 | SiO 4 ] |
|
Mineral class (and possibly department) |
Silicates and germanates - island silicates ( nesosilicates ) |
|
System no. to Strunz and to Dana |
9.AF.85 ( 8th edition : VIII / B.24) 52.03.03.03 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic ( m ) or prismatic (2 / m ) |
| Room group (no.) | Cc or C 2 / c (No. 9 or 15) |
| Lattice parameters |
a = 9.50 Å ; b = 5.48 Å; c = 18.21 Å β = 101.8 ° |
| Formula units | Z = 8 |
| Twinning | polysynthetic twins in parallel [001] |
| Physical Properties | |
| Mohs hardness | 6 to 7 |
| Density (g / cm 3 ) | measured: 3.52 (2); calculated: [3.48] |
| Cleavage | completely after {001}; clearly after {110} |
| Break ; Tenacity | not defined |
| colour | pistachio green, greenish to dark gray |
| Line color | greenish gray |
| transparency | translucent |
| shine | Glass gloss to diamond gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.709 to 1.725 n β = 1.712 to 1.726 n γ = 1.716 to 1.732 |
| Birefringence | δ = 0.007 |
| Optical character | biaxial positive |
| Axis angle | 2V = measured: 46 to 70 °; calculated: 46 to 82 ° |
| Pleochroism | visible: X = olive yellow; Y = light yellow with a greenish tinge; Z = very light yellow to almost colorless |
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 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 part of the manganese in naturally formed ottrelites can be replaced ( substituted ) by iron and / or magnesium , the formula is occasionally also with (Mn 2+ , Fe 2+ , Mg) Al 2 [O | (OH) 2 | SiO 4 ], whereby the elements indicated in the round brackets can represent each other in the formula, but are always in the same proportion to the other constituents of the mineral.
Ottrélith is translucent and rarely develops well-formed, hexagonal-tabular crystals up to about four millimeters in size. It is mostly found in the form of irregular grains or granular aggregates of greenish to dark gray color, which is sometimes also described as pistachio green . Its stroke color is also greenish-gray. Uninjured crystal surfaces show a glass-like luster . However , this can be almost diamond-like on cleavage surfaces .
Etymology and history
Ottrélith was first discovered in the area around Ottré near the municipality of Vielsalm in the Belgian province of Luxembourg . The mineral was first described in 1818 by Laurent-François Dethier and again in 1842 by Alfred Des Cloizeaux and Augustin Alexis Damour .
The mineral was named after its type of locality .
classification
Already in the outdated, but partly still in use 8th edition of the mineral systematics according to Strunz , the Ottrélith belonged to the mineral class of "silicates and germanates" and there to the department of "island silicates with non-tetrahedral anions (Neso subsilicates)", where together with chloritoid and Magnesiochloritoid the "chloritoid group" with the system no. VIII / B.24 .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies the Ottrélith in the category of "island silicates (nesosilicates)". In addition to the possible presence of additional anions, this is further subdivided according to the coordination of the cations involved , so that the mineral is classified according to its composition in the subsection “Island silicates with additional anions; Cations in [4] er, [5] er and / or only [6] er coordination ”can be found, where, together with chloritoid and magnesiochloritoid, the“ chloritoid group ”with the system no. 9.AF.85 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Ottrélith to the class of "silicates and Germanates" and there in the department of "island silicates: SiO 4 groups and O, OH, F and H 2 O". Here it is together with chloritoid, magnesiochloritoid and carboirite in the " chloritoid group " with the system no. 52.03.03 can be found in the subsection “ Island silicates: SiO 4 groups and O, OH, F and H 2 O with cations only in [6] coordination”.
Education and Locations
Ottrélith forms in corridors and cavities of low to medium grade, metamorphic rocks , but can also be precipitated from medium grade hydrothermal solutions . As accompanying minerals may include andalusite different, chlorite , Davreuxit , dickite , kaolinite , pyrophyllite , quartz and rutile occur.
As a rare mineral formation, Ottrélith could only be proven at a few sites, whereby so far (as of 2014) around 60 sites are known. In addition to its type locality Ottré, the mineral occurred in Belgium at Tier des Carrières and Bihain (municipality of Vielsalm ) in the Stavelot massif and in the quarry "Sur les Roches" near Bastogne in the province of Luxembourg and at Rahier (municipality of Stoumont ) in the province of Liège .
In Germany, Ottrélith has so far only been found in a metamorphic rock zone near Wippra and in the Sengelbachtal near Biesenrode in Saxony-Anhalt and near Chemnitz-Rabenstein in Saxony.
Other previously known sites include the “La Pierre Plantée” pass near Mas Aubert in the French department of Gard , the Tignai quarry in the northern Italian community of Bussoleno ; some sites in the communities of Abitibi-Témiscamingue and Les Appalaches in the Canadian province of Québec; the "La Hueca Mine" (Sapo Negro) near Coalcomán de Vázquez Pallares in the Mexican state of Michoacán ; Nyberget ( municipality of Smedjebacken ) in Dalarna, the Västanå iron mine near Näsum ( municipality of Bromölla ) and Vånga ( municipality of Kristianstad ) in Skåne and Ransäter ( municipality of Munkfors ) in Värmland in Sweden, as well as several locations in various states of the USA .
Crystal structure
Ottrélith crystallizes monoclinically in the space group Cc or C 2 / c (space group no. 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 .
See also
literature
- Alfred Des Cloizeaux , Augustin Alexis Damour : De l'ottrélite, nouvelle espèce minérale. In: Annales des Mines. Volume 2 (1842), pp. 357–361 ( PDF 277.6 kB )
- Helmut Schrätze, Karl-Ludwig Weiner: Mineralogy. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 705-706 .
Web links
Individual evidence
- ↑ Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 491 .
- ↑ a b IMA / CNMNC List of Mineral Names; October 2013 (PDF 1.5 MB)
- ↑ a b c d Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 552 .
- ↑ a b c d e Ottrélite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 73.7 kB )
- ↑ a b c Mindat - Ottrélite
- ^ Vaughan DC Daltry, Michel Deliens: The type mineralogy of Belgium. In: Annales de la Société géologique de Belgique. Volume 116 (1993), pp. 15-28 PDF 1.12 MB ; Ottrélith / Ottrelite p. 6)
- ↑ Mindat - Number of localities for Ottrélith
- ↑ Find location list for Ottrélith at the Mineralienatlas and at Mindat