Boehmite
| Boehmite | |
|---|---|
 |
|
| General and classification | |
| chemical formula |
|
|
Mineral class (and possibly department) |
Oxides and hydroxides |
|
System no. to Strunz and to Dana |
4.FE.15 ( 8th edition : IV / F.06) 01/06/02/01 |
| Crystallographic Data | |
| Crystal system | orthorhombic |
| Crystal class ; symbol | orthorhombic-dipyramidal; 2 / m 2 / m 2 / m |
| Space group |
Amam (No. 63, position 4) (also A 2 1 am (No. 36, position 4) )
|
| Lattice parameters | a = 3.693 (1) Å ; b = 12.221 (2) Å; c = 2.865 (1) Å |
| Formula units | Z = 4 |
| Physical Properties | |
| Mohs hardness | 3.5 |
| Density (g / cm 3 ) | measured: 3.02 to 3.05; calculated: [3.08] |
| Cleavage | perfect after {010}, good after {100} |
| colour | white, light yellow, yellow-green, red-brown |
| Line color | White |
| transparency | translucent |
| shine | Glass gloss to pearlescent gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.644 to 1.648 n β = 1.654 to 1.657 n γ = 1.661 to 1.668 |
| Birefringence | δ = 0.017 to 0.020 |
| Optical character | biaxial positive |
| Axis angle | 2V = measured: 74 to 88 °; calculated: 80 ° |
Boehmite is a frequently occurring mineral from the mineral class of " oxides and hydroxides " with the chemical composition AlO (OH) or γ-AlOOH and is therefore an aluminum oxide hydroxide from a chemical point of view .
Boehmite crystallizes in the orthorhombic crystal system , but only rarely develops tabular to short prismatic crystals up to about two millimeters in size. It is mostly found in the form of granular to massive aggregates . In its pure form, boehmite is colorless and transparent. Due to the multiple refraction of light due to the polycrystalline structure in aggregate form, it can also be translucent white and take on a light yellow, yellow-green or red-brown color due to foreign additions. His line color , however, is always white.
Etymology and history
It is unclear whether boehmite was named after the German geologist and paleontologist Johannes Böhm (1857–1938) or after the German-Bohemian chemist and corresponding member of the Czechoslovak Academy of Sciences Johann (Hans, Jan) Böhm (1895–1952).
It was first found and described in 1925 by the chemist Johann Böhm (1895–1952) and the geologist J. de Lapparent in 1927, who called it boehmite.
classification
In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , boehmite belonged to the mineral class of "oxides and hydroxides" and there to the department of "hydroxides and oxidic hydrates", where together with Akaganeit , Diaspor , Feitknechtit , Feroxyhyt , Goethite , groutite , lepidokrokite , manganite , sword mannite and tsumgallite make up the "Akaganeit group" with the system no. IV / F.06 .
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 assigns boehmite to the class of "oxides and hydroxides", but in the department of "hydroxides (without V or U) " a. This is further subdivided according to the possible presence of hydroxide ions (OH) and crystal water (H 2 O) as well as the crystal structure, so that the mineral according to its composition and structure in the sub-section “Hydroxides with OH, without H 2 O; Layers of edge-linked octahedra "can be found, where it is named after the" boehmite group "with the system no. 4.FE.15 and the only other member forms Lepidokrokit.
The systematics of minerals according to Dana also assigns boehmite to the class of "oxides and hydroxides" and there in the department of "hydroxides and hydroxide-containing oxides". Here he is also the namesake of the "boehmite group" with the system no. 06.01.02 and the other members lepidocrocite and guyanaite can be found in the subsection " Hydroxides and hydroxide-containing oxides with the formula: X 3+ O OH ".
Crystal structure
Boehmite crystallizes orthorhombically in the space group Amam (space group No. 63, position 4) (also A 2 1 am (No. 36, position 4) ) with the lattice parameters a = 3.693 (1) Å , b = 12.221 (2) Å and c = 2.865 (1) Å and four formula units per unit cell .
Modifications and varieties
Boehmite is a modification of aluminum hydroxide and is closely related to diaspore (α-AlO (OH)).
Education and Locations
Boehmite, together with diaspore , gibbsite and the iron minerals hematite and goethite, is a component of bauxite .
As a rather rare mineral formation, boehmite can sometimes be abundant at various sites, but overall it is not very widespread, with almost 190 sites known worldwide so far (as of 2017). In Germany, the mineral has so far only been found on Bärenstein in the Ore Mountains. In Austria, boehmite was found at Dreistetten in Lower Austria, in the bauxite deposits of the Untersberg in Salzburg and at Weißwasser in the Reichraminger Hintergebirge in Upper Austria. In Switzerland, the mineral has so far only appeared in the municipality of Collombey-Muraz in the canton of Valais.
Other locations are Australia , Brazil , China , Dominican Republic , France , Ghana , Greece , Greenland , Guyana , Iraq , Israel , Italy , Jamaica , Japan , Cambodia , Canada , Colombia , Madagascar , Mexico , New Zealand , Nigeria , Norway , Russia , Sweden , Slovakia , Sudan , Czech Republic , Turkey , Hungary , the United States of America (USA) and Vietnam .
use
As a component of bauxite, boehmite is an important raw material for the extraction of aluminum .
By careful dehydration (dehydration) of boehmite, aluminum oxide (Al 2 O 3 ) can be produced chemically , which is mainly used for the production of ceramics, as a refractory material or in modern armor for vehicles.
"Boehmite layers" are used for corrosion protection. Correctly created layers (by boiling deionized water or steam) are colorless to milky, largely pore-free, tasteless and completely harmless to health. The pH range is between 3.5 and 9. Boehmite layers protect against attacks from boiling tap water, fruit acids, lactic acids and slightly aggressive foods and beverages. They are also used to protect the inner walls of tanks, heat exchangers and pipe systems, as they can also be applied after installation.
See also
literature
- Jacques de Lapparent: L'alumine hydratée des bauxites . In: Comptes Rendus de L'Académie des Sciences Paris . tape 184 , 1927, pp. 1661–1662 (French, rruff.info [PDF; 151 kB ; accessed on January 31, 2017]).
- William F. Foshag: New mineral names . In: American Mineralogist . tape 13 , 1928, pp. 72–72 ( rruff.info [PDF; 70 kB ; accessed on January 31, 2017]).
- Gary G. Christoph, Charles E. Corbato, Douglas A. Hofmann, Rodney T. Tettenhorst: The crystal structure of boehmite . In: Clays and Clay Minerals . tape 27 , no. 2 , 1979, p. 81–86 ( clays.org [PDF; 505 kB ; accessed on January 31, 2017]).
- Roderick J. Hill: Hydrogen atoms in boehmite: A single crystal X-ray diffraction and molecular orbital study . In: Clays and Clay Minerals . tape 29 , 1981, pp. 435–445 ( clays.org [PDF; 951 kB ; accessed on January 31, 2017]).
Web links
- Mineral Atlas: Boehmite (Wiki)
- RRUFF Database-of-Raman-spectroscopy - Boehmite
- American-Mineralogist-Crystal-Structure-Database - Boehmite
Individual evidence
- ↑ a b IMA List of Mineral Names; November 2016 - Boehmite ( Memento from January 1, 2017 in the Internet Archive ) (English, PDF 1.8 MB; p. 23)
- ^ A b Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 239 .
- ↑ Webmineral (English)
- ↑ a b c Roderick J. Hill: Hydrogen atoms in boehmite: A single crystal X-ray diffraction and molecular orbital study . In: Clays and Clay Minerals . tape 29 , 1981, pp. 435–445 ( clays.org [PDF; 951 kB ; accessed on January 31, 2017]).
- ↑ a b c d Boehmite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 65 kB ; accessed on January 31, 2017]).
- ↑ a b c d e f Mindat - Boehmite (English)
- ↑ Web of Science v České republice: Buletin 04_2000
- ↑ " My dear Hildička!" Conjectures about Hans Böhm. By Peter Lachnit and Heike Possert , radio program Ö1, December 18, 2010
- ↑ Mindat - Number of localities for boehmites
- ↑ Find location list for boehmite in the Mineralienatlas and Mindat