Oligoclase - Occurrence, Properties, and Distribution

Oligoclase, a rock-forming mineral, is a member of the plagioclase feldspars. It has intermediate characteristics between albite and anorthite. The mineral was named by August Breithaupt in 1826 after the Greek words ‘oligos’ and ‘clasein’ which mean little and to break, respectively.

Properties of Oligoclase

The following are the key properties of Oligoclase:

  • Cell Data
    • Space Group: C1 (low)
    • a = 8.152
    • b = 12.821
    • c = 7.139
    • α = 93.99°
    • β = 116.46°
    • γ = 88.58°
    • Z = 4
    • Space Group: C1 (high)
    • a = 8.163
    • b = 12.875
    • c = 7.107
    • α = 93.39°
    • β = 116.27°
    • γ = 90.29°
    • Z = 4
  • Crystal Data
    • Triclinic
    • Point Group: 1
    • Crystals uncommon, flattened and tabular along [010], to 6 cm
    • More commonly cleavable to compact, massive
    • Twinning: Typically twinned according to the Albite, Carlsbad, and Pericline laws.
    • X-ray powder pattern: 3.18 (100), 4.03 (80), 3.20 (80), 3.76 (70), 2.93 (70), 6.38 (60), 3.69 (60)
  • Chemical Composition
    Elements Content 1 Content 2 Content 3
    SiO2 64.92 66.04 60.76
    Al2O3 22.20 21.26 24.82
    Na2O 9.72 10.57 8.12
    CaO 2.64 2.13 6.30
    K2O 0.68 - -
    H2O 0.09 - -
    Total 100.25 100.00 100.00
  • Optical Properties
    • Optical Class: Biaxial (+) or (-)
    • Dispersion: r > v; weak
    • α= 1.533-1.545
    • β= 1.537-1.548
    • γ= 1.542-1.552
    • 2V(meas.) = 84° to -87° to 90°(low); -52° to -73° (high).
  • Estimated Properties
    Electron density Bulk density (electron density)=2.63 g/cm3
    note: Specific gravity of Oligoclase =2.65 g/cm3
    Photoelectric PEOligoclase = 1.98 barns/electron
    U= PEOligoclase x ρElectron density= 5.19 barns/cm3
    Fermion index Fermion index = 0.01
    Boson index = 0.99
    Radioactivity
    Oligoclase is not radioactive

How to Identify Oligoclase

Oligoclase can be identified in greenish, gray, yellowish, brown or colorless forms. This mineral has transparent to translucent appearance. It is a fluorescent mineral with a vitreous lustre, a white streak and perfect cleavages. The fractures on the flat surfaces are uneven. Its granular crystals appear as anhedral to subhedral crystals in a matrix. An excellent external pattern is developed with the well-formed euhedral crystals. The oligoclase has an average density of 2.65 g/cm3 and relative hardness of 7.

A cluster of tabular Oligoclase crystals. Image source:http://en.wikipedia.org/wiki/File:Oligoclase-4jg47a.jpg Original Image: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Global Distribution

Oligoclase is distributed in the following places:

  • Danviken, near Stockholm, Sweden
  • Arendal, on TromÄoy Island at Alve, Tvedestrand
  • Ytterby at Sweden
  • KemiÄo (Kimito) Island, Finland
  • Silberberg, near Bodenmais, Bavaria, Germany
  • Tenerife, Canary Islands
  • Fine and Macomb, St. Lawrence Co., NewYork
  • Corundum Hill, Chester Co
  • Media, Delaware Co., Pennsylvania
  • Bakersville east, near Hawk, Mitchell Co., North Carolina
  • Lake Harbour, Baffin Island, Northwest Territories, Canada.

Occurrence of Oligoclase and Useful Mineral Association

Oligoclase occurs in amphibolite facies metamorphic rocks, gneiss, serpentinite, andesite, rhyolite, sedimentary rocks as clastic grains, syenite, granite and nepheline syenite. It is closely associated with corundum, tourmaline, sanidine, orthoclase and quartz.

References

G.P. Thomas

Written by

G.P. Thomas

Gary graduated from the University of Manchester with a first-class honours degree in Geochemistry and a Masters in Earth Sciences. After working in the Australian mining industry, Gary decided to hang up his geology boots and turn his hand to writing. When he isn't developing topical and informative content, Gary can usually be found playing his beloved guitar, or watching Aston Villa FC snatch defeat from the jaws of victory.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Thomas, G.P.. (2019, September 19). Oligoclase - Occurrence, Properties, and Distribution. AZoMining. Retrieved on October 23, 2019 from https://www.azomining.com/Article.aspx?ArticleID=264.

  • MLA

    Thomas, G.P.. "Oligoclase - Occurrence, Properties, and Distribution". AZoMining. 23 October 2019. <https://www.azomining.com/Article.aspx?ArticleID=264>.

  • Chicago

    Thomas, G.P.. "Oligoclase - Occurrence, Properties, and Distribution". AZoMining. https://www.azomining.com/Article.aspx?ArticleID=264. (accessed October 23, 2019).

  • Harvard

    Thomas, G.P.. 2019. Oligoclase - Occurrence, Properties, and Distribution. AZoMining, viewed 23 October 2019, https://www.azomining.com/Article.aspx?ArticleID=264.

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Submit