Anatase
| Anatase | |
|---|---|
 |
|
| General and classification | |
| other names |
|
| chemical formula | TiO 2 |
|
Mineral class (and possibly department) |
Oxides and hydroxides |
|
System no. to Strunz and to Dana |
4.DD.05 ( 8th edition : IV / D.14) 04.04.04.01 |
| Crystallographic Data | |
| Crystal system | tetragonal |
| Crystal class ; symbol | ditetragonal-dipyramidal; 4 / m 2 / m 2 / m |
| Space group | I 4 1 / amd (No. 141) |
| Lattice parameters | a = 3.78 Å ; c = 9.51 Å |
| Formula units | Z = 4 |
| Frequent crystal faces | usually prismatic according to [001] with {110}, {010} |
| Twinning | rarely after {112} |
| Physical Properties | |
| Mohs hardness | 5.5 to 6 |
| Density (g / cm 3 ) | measured: 3.79 to 3.97; calculated: [3.89] |
| Cleavage | completely according to {001} and {011} |
| Break ; Tenacity | slightly scalloped, brittle |
| colour | black gray, brown to reddish brown, indigo blue, green; rarely colorless |
| Line color | White |
| transparency | transparent to opaque |
| shine | Diamond gloss to metallic gloss |
| Crystal optics | |
| Refractive indices |
n ω = 2.561 n ε = 2.488 |
| Birefringence | δ = 0.073 |
| Optical character | uniaxial negative; abnormally biaxial with strongly colored crystals, s. Notes in the text |
| Pleochroism | mostly weak, but stronger in brightly colored crystals |
Anatase (also octahedral or octahedral Schörl ) is a frequently occurring mineral from the mineral class of " oxides and hydroxides " with the chemical composition TiO 2 and is therefore chemically titanium dioxide .
Anatase crystallizes in the tetragonal crystal system and develops mostly dipyramidal and tabular crystals from a few millimeters to several centimeters in size, the colors of which vary between black-gray, brown, reddish-brown and blue. The colors are based on contamination with foreign atoms ; pure anatase is colorless, but rarely occurs naturally.
Etymology and history
Anatas was named after the Greek word ἀνάτασις anátasis for expansion, stretching or stretching up, since most of the dipyramidal crystals found, in contrast to other tetragonally oriented minerals, show an above-average linear expansion in the direction of the Z-axis.
Blue anatase was first mentioned in 1783 by Jacques Louis de Bournon in a letter to Jean-Baptiste Romé de L'Isle as an indigo blue Schörl . Furthermore, anatase varieties have been described by various scientists and given different names. This is how Horace-Bénédict de Saussure described Octaèdrit , Jean-Claude Delamétherie Oisanit . In 1801, René-Just Haüy first examined colorless anatase, which was found at Le Bourg-d'Oisans in the French department of Isère , and also recognized that the various previously known minerals are varieties of the same mineral that he called anatase .
classification
In the outdated, but still in use 8th edition of the mineral classification according to Strunz , the anatase belonged to the mineral class of "oxides and hydroxides" and there to the department of "oxides with the molar ratio of metal: oxygen = 1: 2", where together with Downeyite it was one formed an independent group.
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 the anatase to the class of "oxides and hydroxides" and there in the department of "metal: oxygen = 1: 2 and comparable "a. However, this section is further subdivided according to the size of the cations involved and the crystal structure, so that the mineral is classified in the sub-section “With medium-sized cations; Scaffolding of edge-linked octahedra “can be found, where it is the only member of the unnamed group 4.DD.05 .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the anatase to the class of "oxides and hydroxides" and there in the department of "oxides". Here it is the only member of the unnamed group 04:04:04 within the subdivision " Simple oxides having a cationic charge of 4 + (AO 2 ) ".
Crystal structure
Anatase crystallizes tetragonally in the space group I 4 1 / amd (space group no. 141) with the lattice parameters a = 3.78 Å and c = 9.51 Å and 4 formula units per unit cell .
Crystal optics
Anatase as a tetragonal crystal is usually described as an optically uniaxial material in accordance with Neumann's principle . Some sources describe a biaxial optical behavior for strongly colored crystals, which is not in accordance with the crystal structure. There are various possible reasons for this:
- Lowering of symmetry through the incorporation of foreign atoms, analogous to the lowering of symmetry in grenades
- Lowering of symmetry due to mechanical stresses that produce stress-induced birefringence.
- Misinterpretation of polarization microscopy results due to the interaction of color and interference figures
Modifications and varieties
The compound TiO 2 is trimorphic and, in addition to the tetragonal anatase, occurs as orthorhombically crystallizing brookite and also as tetragonal, but in a different space group, crystallizing rutile . From 915 ° C anatase changes monotropically to rutile.
Education and Locations
Anatase is usually secondary to the transformation of other titanium-containing minerals in hydrothermal veins and fissures in granite , mica schist , gneiss and diorite , but can also arise in volcanic and metamorphic rocks . Besides brookite and rutile, accompanying minerals are also titanite , ilmenite , titanium-containing magnetite , hematite and quartz . In addition, anatase can be found in the form of pseudomorphoses after titanite and ilmenite. Since the mineral itself transforms into rutile, pseudomorphoses from rutile to anatase are also found.
So far (as of 2011) anatase has been found at around 1500 sites worldwide.
In Germany, anatase was found in the Black Forest (Baden-Württemberg), in the Bavarian Fichtel Mountains as well as in the Swabian-Franconian , Bavarian and Upper Palatinate Forests , in Hesse , in the Harz (Lower Saxony, Saxony-Anhalt, Thuringia), the Eifel (North Rhine-Westphalia , Rhineland-Palatinate), in the Taunus , in Saarland , in the Saxon Ore Mountains , in Schleswig-Holstein and in the Thuringian Forest .
In Austria, the mineral appeared mainly in the regions of Carinthia , Lower Austria , Salzburg , Styria , Tyrol , Upper Austria and Vienna and in Switzerland it was found in the cantons of Bern , Glarus , Graubünden , Canton Ticino , Uri and Valais .
Other locations are Andorra , Antarctica , Argentina , Armenia , Ethiopia , several regions in Australia , Belgium , Bolivia , Brazil , Bulgaria , Chile , China , Ivory Coast , Finland , many regions in France , Cambodia , Cameroon , Greece , Greenland , Guyana , India , Indonesia , Iraq , Ireland , many regions in Italy , Japan , several regions in Canada , Jersey Channel Island , Kazakhstan , Madagascar , Malawi , Morocco , Mexico , Mongolia , Namibia , New Zealand , Niger , North Korea , several regions in Norway , Pakistan , Peru , Poland , Portugal , Réunion , Romania , several regions in Russia , Sweden , Slovakia , Spain , South Africa , Sudan , Czech Republic , Turkey , Uganda , Ukraine , Hungary , Uzbekistan , in several regions of the United Kingdom (Great Britain) as well as in many Regions of the United States of America (USA).
Anatase crystals can also be produced artificially using the CTR process ( chemical transport reactions ).
use
As a pigment
Anatase is used as a white pigment in the colorant industry. It is made using the sulphate process. Due to the higher photocatalytic activity compared to rutile , which leads to the decomposition of organic components, e.g. B. polymers, leads, the area of application is limited. Typical areas of application are photocatalysts, synthetic fibers, food and cosmetic colors E171 and as raw material for industry, e.g. B. special ceramics or glasses . Nanoparticulate anatase is sometimes used in sun protection creams. UV radiation with a wavelength less than about 380 nm is absorbed.
As a gem
Anatase is rarely used as a gem stone because it is very brittle and, due to its good cleavage properties, tends to break when grasped and soldered. But it has a certain value among collectors.
See also
literature
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 104 .
- Walter Schumann: Precious stones and gemstones. All species and varieties in the world. 1600 unique pieces . 13th revised and expanded edition. BLV Verlags GmbH, Munich et al. 2002, ISBN 3-405-16332-3 , p. 228 .
- Roland Hengerer: Single crystal anatase TiO2: growth and surface investigations . Thèse EPFL, no 2272 (2000). Dir .: Michael Graetzel.
Web links
Individual evidence
- ↑ Webmineral - Anatase (English)
- ^ A b c 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. 214 .
- ↑ a b c d e Anatase , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 68.9 kB )
- ↑ a b c Mindat - Anatase (English)
- ↑ Thomas Witzke : Discovery of Schörl. Retrieved May 5, 2013 .
- ↑ René-Just Haüy: Anatase. In: Traité de Minéralogie. 1801, 3, pp. 129–136 ( full text, French ; PDF; 518 kB)
- ↑ polarization optical microscopy on anatase
- ↑ 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. 399 .
- ↑ Areas of application of TiO 2 , source Kronos Titan (PDF; 374 kB)