Allophane
| Allophane | |
|---|---|
 |
|
| General and classification | |
| chemical formula | x Al 2 O 3 · y SiO 2 · z H 2 O x: y = 1: 1 |
|
Mineral class (and possibly department) |
Layered silicates (phyllosilicates) |
|
System no. to Strunz and to Dana |
9.ED.20 ( 8th edition : VIII / H.26) 01.01.04.01 |
| Crystallographic Data | |
| Crystal system | amorphous |
| Physical Properties | |
| Mohs hardness | 3 |
| Density (g / cm 3 ) | measured: 2.75 |
| Cleavage | no |
| Break ; Tenacity | shelly to earthy |
| colour | white, gray, bluish, greenish, brown |
| Line color | White |
| transparency | transparent opaque |
| shine | Glass shine, fat shine, earthy |
| Crystal optics | |
| Refractive index | n = 1.468 to 1.512 (when dry) |
| Optical character | isotropic |
Allophane (also Elhuyarit , Ilbait or Riemannit ) is a mineral from the mineral class of " silicates and germanates ," more specifically, a layer silicate. Along with the well-known opal, it is one of the few minerals that do not belong to a crystal system , but solidify amorphously .
Its chemical composition is x Al 2 O 3 · y SiO 2 · z H 2 O, where the variables x and y have a ratio of 1: 1. The molecular groups aluminum oxide and silicon dioxide as well as the water of crystallization they contain occur in different contents.
Allophane forms grape, stalactitic or earthy mineral aggregates of white, gray, bluish, greenish and brown color with white streak color .
Etymology and history
The name allophane is derived from the Greek words ἄλλος allos for "other" and φαίνεσθαι phainesthai for "appear", means something like "that which appears as another" and refers to the often existing similarity with other copper minerals.
Allophane was first discovered near Graefenthal in the Saalfeld-Rudolstadt district in Thuringia and described in 1816 by JFL Hausmann and F. Stromeyer : About Silberkupferglanz and Allophan , Göttingische Gelehre Anzeige 2, pp. 1251–1253.
classification
In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of allophane belonged to the mineral class of "silicates and Germanates" and then to the Department of " phyllosilicates (phyllosilicates)" where he collaborated with Hisingerite , Imogolith , Neotokit and Odinit a 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 allophane to the class of “silicates and germanates” and there to the “phyllosilicates” section. This division is, however, further subdivided according to the crystal structure, so that the mineral, according to its structure, can be found in the sub-division of "phyllosilicates (phyllosilicates) with kaolinite layers, composed of tetrahedral or octahedral networks", where it can be found together with bismuth ferrite , chapmanite , chrysocolla , Imogolith and Neotokit the "Chapmanite group" with the system no. 9.ED.20 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the allophane to the class of "silicates and Germanates" and there in the department of "layered silicate minerals". Here he is the namesake of the "allophane group" with the system no. 71.01.04 and the other members Hisingerite, Imogolite, Neotocite and Zinalsite can be found within the sub-section “ Layered Silicates: Layers of six-membered rings with 1: 1 layers ”.
Crystal structure
Allophane solidifies in amorphous or semi-crystalline form with aluminum [6], [5] and [4] coordination .
properties
Due to its loose structure with many cavities and the high water content, allophane has a very low density (dry bulk density of allophane-containing soils <0.9 g / cm³). In addition, it has a very high reactive surface (~ 800 m² / g), which is mainly formed by " pores " in the hollow spheres (actually defective areas that interrupt the hollow spheres). Desiccation and water loss lead to irreversible structural destruction.
Allophane is infusible in front of the soldering tube.
The two main types of aluminum-rich allophane (Al: Si, 2: 1) and silicon-rich allophane (Al: Si, 1: 1) arise depending on the availability of the substances in the soil solution.
Education and Locations
Allophane is mainly produced hydrothermally in crevices in sedimentary rocks . During soil formation, it is created in particular by the chemical weathering of volcanic glass and then forms so-called loose brown earth. Allophane can also be found in coal and ore deposits. Accompanying minerals include chrysocolla , cristobalite , gibbsite , imogolite, limonite , quartz and vermiculite .
In total, allophane has so far (as of 2011) been detected at around 370 sites. In addition to its type locality Graefenthal, the mineral was also found in Germany in several places in the Black Forest in Baden-Württemberg; near Pechbrunn and Kropfmühl in Bavaria; Goldhausen and Kirschhausen in Hesse; in several places in the Harz Mountains from Lower Saxony to Saxony-Anhalt; near Untermaubach , Wülfrath and in several places in the Sauerland and Siegerland in North Rhine-Westphalia; near Antweiler in Rhineland-Palatinate; near Chemnitz-Markersdorf and Mechelgrün as well as in several places in the Ore Mountains in Saxony and near Gera , Garnsdorf ( Saalfeld / Saale ), on the Bergmannskopf near Graefenroda , near Brotterode-Trusetal and Weckersdorf in Thuringia.
In Austria, Allophan performed at Pauliberg in Burgenland, among others ; near Leoben in Styria, and near Freistadt in Upper Austria as well as in several places in the regions of Carinthia , Salzburg and Tyrol .
In Switzerland, the mineral found on Cavloc Lake in Fornotal (Valley of the Fornogletschers ) in the canton of Grisons and in Ayer (Val d'Anniviers) , Saint-Luc VS and Sierre ( Granges ) in the canton of Valais.
Other locations are Argentina , Australia , Moldova , Belgium , Bolivia , China , Ecuador , France , Greece , Ireland , Israel , Italy , Japan , Kazakhstan , Kyrgyzstan , Canada , Colombia , the Democratic Republic of the Congo , Mexico , New Zealand , the Netherlands , Norway , Poland , Romania , Russia , Zambia , Serbia , Zimbabwe , Slovakia , Spain , South Africa , Taiwan , Czech Republic , Turkmenistan , Ukraine , Hungary , United Kingdom (Great Britain) and United States of America (USA).
Allophane could also be detected in rock samples from the East Pacific Ridge .
See also
literature
- JFL Hausmann , F. Stromeyer : Report at the Royal Academy of Sciences Göttingen meeting 13 July, 1816 on silver copper luster and allophan . In: Göttingische Scholars Ads . tape 2 , 1816, p. 1249–1253 ( rruff.info [PDF; 346 kB ; accessed on August 7, 2017]).
- F. Stromeyer: Analysis of the sels de strontiane et de quelques mineraux . In: Annales de Chimie et de Physique . tape 3 , 1816, p. 395–403 ( rruff.info [PDF; 379 kB ; accessed on August 7, 2017]).
- Roger L. Parfitt, RJ Furkert, T. Henmi: Identification and structure of two types of allophane from volcanic ash soils and tephra . In: Clays and Clay Minerals . tape 28 , 1980, pp. 328-334 .
- Roger L. Parfitt: Allophane in New Zealand - a review . In: Australian Journal of Soil Research . tape 28 , 1990, pp. 343-360 , doi : 10.1071 / SR9900343 .
- Fritz Scheffer: Textbook of soil science . 15th edition. Spectrum, Akademischer Verlag, Heidelberg, Berlin 2002, ISBN 978-3-8274-1324-6 .
- Petr Korbel, Milan Novák: Mineral Encyclopedia (= Villager Nature ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 259 .
Web links
- Mineral Atlas: Allophane (Wiki)
- Webmineral - Allophane (English)
- RRUFF Database-of-Raman-spectroscopy - Allophane (English)
- Thomas Witzke : Discovery of Allophane
Individual evidence
- ↑ a b allophanes . 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; 72 kB ]).
- ^ 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. 676 .
- ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 760–761 (first edition: 1891).
- ↑ Mindat - Number of locations for Allophane (English)
- ↑ a b List of locations for allophane in the Mineralienatlas and Mindat