Diaspore

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Diaspore
Diaspore-Margarite-215043.jpg
Diaspor and Margarit from Muğla, Aegean Region, Turkey (size: 3.8 cm × 2.6 cm × 2.3 cm)
General and classification
chemical formula α-AlOOH
Mineral class
(and possibly department) 		Hydroxides and oxide hydrates
System no. to Strunz
and to Dana 		4.FD.10 ( 8th edition : IV / F.06)
01/06/01/01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Pbnm (No. 62, position 3)Template: room group / 62.3
Lattice parameters a  = 4.40  Å ; b  = 9.42 Å; c  = 2.84 Å
Formula units Z  = 4
Twinning to {021}
Physical Properties
Mohs hardness 6.5 to 7
Density (g / cm 3 ) 3.3 to 3.5
Cleavage perfectly
Break ; Tenacity clamshell; very brittle
colour colorless, white, wine yellow, pink, reddish, violet, gray
Line color White
transparency transparent to translucent
shine Glass gloss, pearlescent gloss
Crystal optics
Refractive indices n α  = 1.682 to 1.706
n β  = 1.705 - 1.725
n γ  = 1.730 to 1.752
Birefringence δ = 0.048
Optical character biaxial positive
Axis angle 2V = 84 to 86 ° (measured); 80 to 84 ° (calculated)
Pleochroism strong: X = violet blue; Y = light green; Z = pink to dark red

Diaspor (also called diasporite ) is a rather seldom occurring mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the orthorhombic crystal system with the chemical composition AlO (OH) or α-AlOOH and develops mostly leafy, granular or massive aggregates , but also small, finely striped crystals up to about 12 cm in size in wide columns with a predominantly developed longitudinal surface.

Pure diaspore is colorless. However, it can be white to gray, yellow, pink, green, reddish to violet or brownish in color due to foreign admixtures. Its Mohs hardness is 6.5 to 7 and its density 3.3 to 3.5 g / cm³.

Diaspor is sometimes confused with the lead silver antimonite diaphorite due to the similarity of its name .

Etymology and history

The name diaspore is derived from the Greek word διασπείρειν (diaspeirein) for disperse . With the name chosen in his mineral description in 1801, René-Just Haüy wanted to refer to its property of atomizing or shattering into small particles when heated in front of the soldering tube , releasing water. This property is also called decrepitation ( decrepitation called).

The type locality is Mramorskii Zavod (Mramorsk Zavod, Мраморский Завод) near the city of Yekaterinburg in the Russian Oblast of Sverdlovsk .

classification

In the 8th edition of the mineral systematics according to Strunz , which is outdated, but still in use , the diaspor belonged to the mineral class of "oxides and hydroxides" and there to the department of "hydroxides and oxidic hydrates", where together with akaganeit , boehmite , feitknechtite , feroxyhyte , Goethite , groutite , lepidokrokite , manganite , sword mannite and tsumgallite formed the unnamed group IV / F.6 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), assigns the diaspore to the class of "oxides and hydroxides" and then to the department of "hydroxides (without V or U)" . However, this section is further subdivided according to the possible presence of crystal water and according to the crystal structure, so that the mineral is classified in the sub-section “Hydroxides with OH, without H 2 O; can be found with chains of edge-sharing octahedra "where it along with Bracewellit , goethite, Groutit, Guyanait , montroseite and Tsumgallit the unnamed group 4.FD.10 forms.

The systematics of minerals according to Dana also assigns the diaspore to the class of "oxides and hydroxides" and there into the department of "hydroxides and hydroxides containing oxides". Here the diaspor is named after and with the other members Groutit, Montroseit, Bracewellit and Tsumgallit in the "Diaspor group (Orthorhombic, Pnma or Pnmd)" with the system no. 06.01.01 to be found within the sub-section of " Hydroxides and hydroxide-containing oxides with the formula: X 3+ O OH ".

Crystal structure

Structure of diaspore, viewing direction almost parallel to the c-axis. Hydrogen bonds are highlighted in green.
  • H
  • Al 3+
  • O 2−

    • Diaspore crystallizes in orthorhombically in the space group Pbnm (space group no. 62, position 3) , the lattice parameters a  = 4.40  Å , b  = 9.42 Å and c  = 2.84 Å and four formula units per unit cell . Template: room group / 62.3

    Oxygen and hydroxide ions form a hexagonal close packing of spheres with gaps in the octahedron spaces that are filled by aluminum. In this way, long double chains of AlO 6 octahedra are formed in the direction of the c-axis , which are held together by hydrogen bonds .

    properties

    Diaspore shows strong pleochroism , that is, it appears purple-blue in the direction of the x-axis, light green in the direction of the y-axis and pink to dark red in the direction of the z-axis.

    Chemically, diaspore consists essentially of aluminum hydroxide Al 2 O 2 (OH) 2 or AlO (OH), with 85.02% alumina and 14.98% water and some iron oxide. It turns blue with cobalt solution, acids do not dissolve it and only after a strong glow does it become soluble in sulfuric acid.

    Modifications and varieties

    Bright red manganese diaspore from the Wessels Mine, Hotazel , Kalahari Manganese fields, North Cape, South Africa (size: 6.9 cm × 5.7 cm × 4.9 cm)

    The compound AlO (OH) is dimorphic , so it occurs in nature in addition to the orthorhombically crystallizing diaspore also as orthorhombic boehmite , but in a different space group crystallizing boehmite .

    Various varieties of diaspore are known:

    • Chromium diaspore contains small amounts of the element chromium and is therefore light to dark purple in color
    • Manganese diaspore contains additions of manganese , which gives the mineral a pink to dark red color

    Education and Locations

    Diaspor twin from Selçuk, Muğla Province, Aegean Region, Turkey (size: 3.6 cm × 3.6 cm × 2.6 cm)

    Diaspore forms either hydrothermally or metamorphically from aluminum-rich minerals or in aluminum-rich rocks . Accompanying minerals include pyrophyllite and corundum . Diaspore is also a part of the mixture of bauxite .

    Diaspor is one of the seldom occurring mineral formations, some of which can be abundant at different sites, but overall are not very common. A total of around 440 sites are known to date (as of 2015). In addition to its type locality Mramorskii Zavod and other places in the Urals Federal District , the mineral appeared in Russia at various sites in Eastern and Western Siberia , the Far Eastern Republic and in the Northwestern Federal District.

    In Germany, the mineral has so far only been found on Silberberg near Bodenmais in Bavaria and near Vierkirchen (Oberlausitz) , Königshain , Hetzdorf-Landberg / Mohorn (municipality of Wilsdruff ) and Callenberg in Saxony.

    In Austria, diaspores were found at Untere Grabner near Lölling in Carinthia, at Marchgraben near Dreistetten and near Wolfsbach and Zissersdorf in the municipality of Drosendorf-Zissersdorf in Lower Austria, in a bauxite pit at the northern foot of the Untersberg above Glanegg (market town of Grödig ) in the Salzburger Land, in a bauxite deposit near Hieflau and on the Brandberg near Leoben in Styria, near Brandenberg in the Inn Valley and on the Großer Greiner in the Zillertal in Tyrol.

    In Switzerland, the mineral is so far only known from Brunnihore (municipality of St. Stephan BE ) in the canton of Bern, Venett / Campolungo in Val Piumogna in the canton of Ticino and Pointe de Dréveneuse (municipality of Collombey-Muraz ) in the Valais.

    The Menderes River near Yatağan in the Turkish province of Muğla , where tabular crystals up to 12 cm in size were found, is worth mentioning due to the extraordinary finds of diaspore .

    Other locations include the Antarctic, Argentina, Australia, Bolivia, Brazil, Bulgaria, Chile, China, the Dominican Republic, Ecuador, Finland, France, Greece, Greenland, India, Indonesia, Italy, Japan, Cambodia, Canada, Kazakhstan, Madagascar, Malawi, Malaysia, Morocco, Macedonia, Mongolia, Myanmar (Burma), Namibia, New Zealand, Norway, Papua New Guinea, Peru, the Philippines, Portugal, Romania, the Solomon Islands, Sweden, Serbia, the Slovakia, Slovenia, Spain, South Africa, South Korea, Sudan, Swaziland, Taiwan, Tanzania, Czech Republic, Hungary, Uruguay, the United Kingdom (UK) and the United States of America (USA).

    use

    Diaspor as a color changing gemstone from Turkey, 2.92ct

    Diaspor is used as an abrasive and polishing agent .

    In the jewelry industry, diaspora is often sold as a gemstone under the brand name zultanite. Diaspore occasionally shows a color change from green in daylight to yellow to orange in artificial light.

    See also

    literature

    In compendia:

    • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 551 (first edition: 1891).
    • Martin Okrusch, Siegfried Matthes: Mineralogy. An introduction to special mineralogy, petrology and geology . 7th, completely revised and updated edition. Springer, Berlin [a. a.] 2005, ISBN 3-540-23812-3 , pp. 58 .

    Scientific articles:

    • Roderick J. Hill: Crystal structure refinement and electron density distribution in diaspore . In: Physics and Chemistry of Minerals . tape 5 , no. 2 , 1979, p. 179-200 , doi : 10.1007 / BF00307552 .

    Web links

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

    Individual evidence

    1. ↑ a b c d 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.  235 .
    2. ↑ a b c d e Mindat - Diaspore
    3. ^ A b Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 50 .
    4. ^ IMA / CNMNC List of Mineral Names; July 2015 ( Memento from September 5, 2015 in the Internet Archive ) (PDF 1.5 MB; p. 48)
    5. ↑ Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 203 .
    6. ^ RJ Haüy: VII. Diaspore (center), c'est-à-dire, qui se disperse . In: Traité de Minéralogie . tape 4 . Chez Louis, Paris 1801, p. 358–360 ( rruff.info [PDF; 326 kB ]).
    7. ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  486 .
    8. ^ Mineral Atlas: Diaspor
    9. ↑ Diaspore . 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; 64  kB ; accessed on April 6, 2018]).
    10. ↑ Mindat - Number of localities for diaspore
    11. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 109 .
    12. ↑ Mindat - example of a 12 cm diaspore crystal from Menderes, Yatağan, Muğla, Turkey
    13. ↑ Find location list for Diaspor in the Mineralienatlas and in Mindat
    14. ↑ Name search. Trade names and what they mean. EPI - Institute for Gemstone Testing , accessed on April 6, 2018 (entry of zultanite required).