Dickit

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Dickit
Dickite-262230.jpg
Dickit from the "Magmont Mine", Bixby , Iron County (Missouri) , USA ( overall size : 7.0 × 4.5 × 4.2 cm)
General and classification
chemical formula Al 4 [(OH) 8 | Si 4 O 10 ]
Mineral class
(and possibly department)
Silicates and Germanates
System no. to Strunz
and to Dana
9.ED.05 ( 8th edition : VIII / H.25)
71.01.01.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic; m
Room group (no.) Cc (No. 9)
Lattice parameters a  = 5.15  Å ; b  = 8.94 Å; c  = 14.42 Å
β  = 96.7 °
Formula units Z  = 2
Physical Properties
Mohs hardness 2 to 2.5
Density (g / cm 3 ) measured: 2.60; calculated: [2.62]
Cleavage completely after {001}
Break ; Tenacity uneven
colour white, yellowish
Line color White
transparency transparent
shine Silky gloss
Crystal optics
Refractive indices n α  = 1.561 to 1.564
n β  = 1.561 to 1.566
n γ  = 1.566 to 1.570
Birefringence δ = 0.005 to 0.006
Optical character biaxial positive
Axis angle 2V = 50 to 80 ° (measured); 72 to 80 ° (calculated)

Dickit is a rather seldom occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the monoclinic crystal system with the chemical composition Al 4 [(OH) 8 | Si 4 O 10 ], so from a chemical point of view it is an aluminum silicate with additional hydroxide ions . Structurally, it belongs to the layered silicates .

Dickit only develops small, tabular and pseudo-hexagonal crystals a few millimeters in diameter. It is mostly found in the form of platy, earthy or massive mineral aggregates , whereby the stacked crystal tablets occasionally have a book-like appearance. In its pure form, Dickit is colorless and transparent. However, since it occurs predominantly in polycrystalline form , it usually appears white with a silk-like sheen on the surfaces due to multiple refraction . However , it can also take on a yellowish color as a result of foreign admixtures, whereby the transparency decreases accordingly.

Etymology and history

Dickit was first discovered in the "Pant-y-Gaseg" mine near Amlwch on the island of Anglesey off the north-west coast of Wales . The mineral was first described by the Scottish metallurgist and chemist Allan Brugh Dick (1833-1926), who dealt with the Anglesey minerals in general and described their properties in detail. In 1930 Clarence S. Ross and Paul F. Kerr took up his report and named the newly discovered mineral after the person who first described it.

classification

In the meantime outdated, but still in use 8th edition of the mineral classification by Strunz of dickite belonged to the department of " phyllosilicates (phyllosilicates)," where he, together with halloysite 7 Å , 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 assigns Dickit to the category of "phyllosilicates". This is, however, further subdivided according to the layer structure, so that the mineral, according to its structure, can be found in the sub-section "Layered silicates (phyllosilicates) with kaolinite layers, composed of tetrahedral or octahedral networks", where together with kaolinite, nacrite and odinite it forms the "kaolinite group “With the system no. 9.ED.05 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking area , also classifies the Dickit in the "layered silicate minerals" department. Here it is together with kaolinite, nakrite, halloysite-7Å, 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 ”.

Crystal structure

Dickite crystallizes monoclinically in the space group Cc (space group no. 9) with the lattice parameters a  = 5.15  Å ; b  = 8.94 Å; c  = 14.42 Å and β = 96.7 ° as well as two formula units per unit cell .

properties

When heated, loses dickite above a temperature of 510 ° C to 575 ° C be constitutionally bound water of crystallization .

Modifications and varieties

Dickite forms a polymorphic series with halloysite-7Å, kaolinite and nakrite , which means that all minerals have the same chemical composition, but crystallize in different crystal systems or within a crystal system in different space groups .

Education and Locations

Dickit from Mas d'Alary, Lodève , France (size: 4.2 × 3.8 × 2.8 cm)

Dickite forms in cavities in hydrothermal veins , where it usually occurs in paragenesis with quartz or its variety chalcedony and with various carbonates and / or sulfides.

As a rather rare mineral formation, Dickite can sometimes be abundant at various sites, but overall it is not very common. Around 500 sites are known to date. In addition to its type locality "Pant-y-Gaseg" near Amlwch , the mineral occurred in the United Kingdom in several places in the English counties of Cornwall and Cumbria , near Lochgilphead in the Scottish region of Strathclyde and in other places in Wales such as the Rhondda Cynon Open up.

Significant amounts of the mineral were discovered at Kara Čeku in central Kazakhstan , among others .

In Germany, the mineral could be found in Wildschapbachtal and near Triberg in the Black Forest in Baden-Württemberg, near Sankt Andreasberg in Lower Saxony, in several places in the Bergisches Land , the Ruhr area , in the Sauerland and Siegerland in North Rhine-Westphalia, in many places in the Eifel from North Rhine-Westphalia to Rhineland-Palatinate, in some places in the Saxon Ore Mountains (Altenberg, Schneeberg) and near Ronneburg and Weida in Thuringia.

In Austria, Dickit has so far only been found in a few locations in Carinthia, among others in the Kreuzeck group and near Bleiburg , in the Salzburg Hohe Tauern as well as in the municipality of Sankt Stefan ob Leoben and the Murau district in Styria.

In Switzerland, the mineral has so far been found in the municipality of Scuol , in Splügen (municipality of Rheinwald ) and the Val Renastga in the canton of Graubünden, in the "Lengenbach mine" in the Binn valley in the canton of Valais and in rock samples near Airolo that were examined during the construction of the Gotthard tunnel were.

Other sites are in Afghanistan, Argentina, Armenia, Australia, Belgium, Bolivia, Brazil, Bulgaria, Chile, China, Ecuador, France, Georgia, Greece, India, Indonesia, Italy, Japan, Canada, Kazakhstan, in Kosovo, in Kyrgyzstan, Luxembourg, Malaysia, Morocco, Mexico, Mongolia, the Netherlands, New Zealand, Norway, Panama, Papua New Guinea, Peru, the Philippines, Poland, Romania, Russia, Sweden, Serbia, Slovakia, Spain, South Africa, South Korea, Tajikistan, Turkey, the Czech Republic, Ukraine, Hungary, Uzbekistan, the United Kingdom (Great Britain) and the United States of America (USA).

See also

literature

  • Clarence S. Ross, Paul F. Kerr: Dickite, a kaolin mineral , In: American Mineralogist , Volume 15 (1930), pp. 34–39 ( PDF 309.4 kB )
  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 257 ( Dörfler Natur ).

Web links

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

Individual evidence

  1. 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.  675 .
  2. Webmineral - dickites
  3. a b c Dickite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 74.3 kB )
  4. a b c Mindat - Dickite
  5. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke , Stuttgart 1978, ISBN 3-432-82986-8 , pp.  759 (first edition: 1891).
  6. Mindat - Number of localities for Dickite
  7. 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.  565 .
  8. List of localities for Dickit in the Mineralienatlas and Mindat