Oligoclase

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Oligoclase
Oligoclase-4jg47a.jpg
Oligoclase from Chihuahua , Mexico
General and classification
chemical formula
  • (Na, Ca) [(Si, Al) 4 O 8 ]
  • (Ca, Na) [(Al, Si) 2 Si 2 O 8 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.FA.35 ( 8th edition : VIII / J.07)
76.01.03.02
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group C 1 (No. 2, position 3)Template: room group / 2.3
Lattice parameters a  = 8.16  Å ; b  = 12.82 Å; c  = 7.14 Å,
α  = 94.0 °; β  = 116.5 °; γ  = 88.6 °
Formula units Z  = 4
Twinning Carlsbad and Periclin twins similar to the albite
Physical Properties
Mohs hardness 6 to 6.5
Density (g / cm 3 ) measured: 2.63 to 2.66; 2.624 to 2.652
Cleavage perfect after {001}, imperfect after {010} and {110}
Break ; Tenacity shell-like to uneven; brittle
colour colorless, white, yellow, red, green, multicolored
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Birefringence δ = 0.007
Optical character biaxial positive
Pleochroism colorless
Other properties
Special features fluorescence

Oligoclase is a very common mixed crystal from the series of "plagioclase" with the end members albite and anorthite . Like this, oligoclase belongs to the group of feldspars within the mineral class of " silicates and germanates ".

Until 2009, oligoclase was still listed as a so-called intermediate member of the International Mineralogical Association (IMA) , but is not considered an independent mineral species and is also viewed in some sources as a variety of albite.

Oligoclase consists of 70–90% albite or 10–30% anorthite with the chemical composition (Na, Ca) [(Si, Al) 4 O 8 ]. It crystallizes in the triclinic crystal system and is usually found ingrown in granular mineral aggregates with different colors from yellow to red, green or even multicolored depending on the foreign admixture.

Etymology and history

The name Ologoklas was coined by August Breithaupt in 1826 and is made up of the Greek words ὀλίγος oligos for “little” and κλάω klas for “break” or “split”, which means “little splitting” or “less easily split”. The name refers to the property of cleavage , which is less pronounced in oligoclase than in other feldspars, especially albite ( tetartin ).

Varieties and modifications

Natural sunstone from India

The variety aventurine feldspar or sunstone has a reddish-brownish color and glitters strongly through microcrystalline inclusions of hematite and other iron oxides. It is often confused with aventurine quartz and imitated by the flow of gold .

Education and Locations

Oligoclase is a typical, rock-forming mixed crystal and forms either igneously in granite , syenite , andesite or pegmatite and metamorphically in gneiss or migmatite .

The main locations are Ontario in Canada , Oregon in the USA , Arendal and Tvedestand in Norway , the Urals in the Russian Federation , Badajoz in Spain and Vežná in the Czech Republic .

use

Oligoclase in various shapes

Colorless oligoclase in gem quality is rarely found. In addition, due to its ability to be completely split, it is sensitive to pressure and the effects of heat during barrel and repair work. For collectors, however, it is occasionally offered in different shapes .

The sunstone variety is processed into gemstones. It occurs for example in India, Norway, South Africa and the USA and is often imitated. The best known imitation is the so-called gold river (also gold stone or aventurine glass ). Copper or hematite in microcrystalline form is added to molten glass . The process was already practiced by Venetian glass manufacturers in the 17th century . After cooling, the broken pieces of glass are cut into various gemstone shapes or processed into tumbled stones.

See also

List of minerals

literature

  • U. Kraeft, H. Saalfeld: About the aventurine oligoclase from Tvedestrand and Bjordam (Norway) . In: Switzerland. Min. And Petr. Mitt. Band 47 , 1967, p. 247-256 .
  • Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Villager Nature ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 265 .
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 783 (first edition: 1891).
  • Bernhard Bruder: Beautified stones. Recognizing imitations and manipulations in gemstones and minerals . Neue Erde Verlag, 2005, ISBN 978-3-89060-079-6 , pp. 45 .

Web links

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

Individual evidence

  1. ^ A b c 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 .
  2. ^ Berthold Ottens , Michael Huber: Chemistry, Structure & Properties . In: Feldspar. The most common mineral (= Christian Weise [Hrsg.]: ExtraLapis . Volume  30 ). Christian Weise Verlag, 2010, ISSN  0945-8492 , p. 64 .
  3. ↑ The numbering of this axis position does not correspond to the order of the International Tables for Crystallography , because it is not listed there.
  4. ↑ a b c d oligoclase . 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; 85  kB ; accessed on November 1, 2017]).
  5. ↑ IMA / CNMNC List of Mineral Names 2009 (PDF 1.8 MB)
  6. ↑ Mineral Atlas: Oligoclase (Wiki)
  7. ↑ Mindat - Oligoclase (English)
  8. ↑ 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. 285 .
  9. ↑ August Breithaupt : Comments on the sex of the feldspar - Grammit's and description of the oligoclase, a new species of the same . In: Annals of Physics and Chemistry . tape  8 , 1826, pp. 231–242 ( rruff.info [PDF; 565 kB ; accessed on November 1, 2017]).