Halloysite-7Å

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Halloysite
Mineraly.sk - halloyzit.jpg
Halloysite
General and classification
other names
  • Endellite
  • Metahalloysite
  • Pelicanite
chemical formula Al 4 [(OH) 8 | Si 4 O 10 ]
Mineral class
(and possibly department)
Silicates and germanates - sheet silicates (phyllosilicates)
System no. to Strunz
and to Dana
9.ED.10 ( 8th edition : VIII / H.25)
01/01/01/04
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic; m
Room group (no.) Cc (No. 9)
Lattice parameters a  = 5.14  Å ; b  = 8.90 Å; c  = 14.9 Å
β  = 101.9 °
Formula units Z  = 2
Physical Properties
Mohs hardness 2 to 2.5
Density (g / cm 3 ) 2.55 to 2.65 / average 2.59
Cleavage is missing
Break ; Tenacity shell-like
colour white, gray, yellowish, reddish, greenish, bluish, brownish
Line color White
transparency translucent to opaque
shine Wax gloss

Halloysite-7Å (also metahalloysite or endellite ) is a mineral from the mineral class of " silicates and germanates ", more precisely a layered silicate (phyllosilicate) with the chemical composition Al 4 [(OH) 8 | Si 4 O 10 ]. It crystallizes in the monoclinic crystal system and develops exclusively bulbous or earthy aggregates in white, gray, yellowish, reddish, greenish, bluish or brownish color.

Special properties

Halloysit-7Å shows some parallels with kaolinite . A distinction is made, however, by treating the sample with glycerine or urea . The crystal lattice is expanded so that a distinction between the halloysite-10Å and kaolinite produced by means of X-ray diffraction is clear.

Etymology and history

Halloysite was first discovered near Angleur / Liège in Belgium and described in 1826 by Pierre Berthier , who named the mineral after the Belgian geologist JBJ Baron d'Omalius d'Halloy (1707–1789).

classification

In the outdated but still partially in use 8th edition of the mineral classification by Strunz of halloysite 7 Å belonged to the department of " phyllosilicates (phyllosilicates)" where he collaborated with dickite , kaolinite and nacrite the "kaolinite" with the system no. VIII / H.25 .

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 halloysite-7Å in the “phyllosilicates” department. However, this is further subdivided according to the crystal structure, so that the mineral, according to its structure, can be found in the subdivision of "layered silicates (phyllosilicates) with kaolinite layers, composed of tetrahedral or octahedral networks", where it is named together with halloysite-10Å as the namesake Halloysite group "with the system no. 9.ED.10 and the other member Hisingerit forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns halloysite-7Å to the “layered silicate minerals” department. Here it is together with dickite, kaolinite, nakrite, endellite and odinite in the "kaolinite group" with the system no. 71.01.01 can be found in the sub-section “ Layered Silicates: Layers of six-membered rings with 1: 1 layers ”.

Education and Locations

Halloysite-7Å is formed either through the weathering of volcanic glasses or through hydrothermal processes . As a component of many clays and soils, halloysite is also counted among the clay minerals .

As a rare mineral formation, halloysite-7Å has so far (as of 2012) only been proven at a few sites, with around 20 sites being known. Its type locality Angleur is the only known site in Belgium so far.

In Germany, the mineral has so far been found at Thelenberg and In den Dellen near Mendig in the Eifel and in the Käusersteimel pit near Kausen in the Siegerland.

Other locations include China, Indonesia, New Zealand, Peru, Russia and the United States of America.

Crystal structure

Halloysite-7Å crystallizes monoclinically in the space group Cc (space group no. 9) with the lattice parameters a  = 5.14  Å ; b  = 8.90 Å; c  = 14.9 Å and β = 101.9 ° as well as 2 formula units per unit cell .

See also

literature

  • Bernd Schwaighofer: On the weathering of volcanic rocks - a contribution to halloysite genesis , in: Mitteilungen der Geologische Gesellschaft in Wien , 66. – 67. Volume, 1973/74 ( PDF 1.6 MB ).

Web links

Commons : Halloysite  - collection of images, videos and audio files

Individual evidence

  1. Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 5th completely revised and supplemented edition. Weise, Munich 2008, ISBN 978-3-921656-70-9 .
  2. a b c d e 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.  676 .
  3. Webmineral - Halloysite (English)
  4. Martin Okrusch, Siegfried Matthes: Mineralogie: An introduction to special mineralogy, petrology and deposit science . 7th edition. Springer Verlag, Berlin, Heidelberg, New York 2005, ISBN 3-540-23812-3 , pp. 107 .
  5. Mindat - Number of localities for halloysite-7Å
  6. Mindat - Halloysite-7Å