Oligoclase

Big Photo

Kenya
2.57 carats
© Rarestone.com

A feldspar comprising 70-90% Albite and 10-30% Anorthite.

The name oligoclase derived from the Greek "oligos" - little, and "clasein" - to break, because the mineral was thought to have a less perfect cleavage than albite. This name was given by August Breithaupt in 1826.

Oligoclase Gemstones by Colour

This table shows the variety of hues this gemstone can be found in. Click on a photo for more information.
 
 
 

Oligoclase Gemstones by Size

This table shows distribution of Oligoclase gemstone sizes that are listed on this site. This can give a good indication as to the general availability of this gemstone in different sizes.
Contributed photos
Lightest:0.74 cts
Heaviest:8.95 cts
Average:2.90 cts
Total photos:21
Do you have a larger Oligoclase? Why not upload a photo?
0.74ct to 1.56ct1.56ct to 2.38ct2.38ct to 3.20ct3.20ct to 4.02ct4.02ct to 4.85ct4.85ct to 5.67ct5.67ct to 6.49ct6.49ct to 7.31ct7.31ct to 8.13ct8.13ct to 8.95ct
General Information
A variety or type of:Feldspar
Chemical Formula
Na(90-70%)Ca(10-30%)(Al,Si)AlSi
 
2
O
 
8
Michael O’Donoghue, Gems, Sixth Edition (2006)
Photos of natural/un-cut material from mindat.org

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Oligoclase Treatments
Irradiation may turn colourless material blue if lead and water impurities are present (see amazonite). Oligoclase has also been reported to turn orange and green upon irradiation.
Physical Properties of Oligoclase
Mohs Hardness6 to 6.5
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
More from other references
Specific Gravity2.62 to 2.67
Walter Schumann, Gemstones of the world (2001)
More from other references
Cleavage QualityPerfect,Good
Michael O’Donoghue, Gems, Sixth Edition (2006) Perfect in one and good in another direction
FractureConchoidal
Michael O’Donoghue, Gems, Sixth Edition (2006)
Optical Properties of Oligoclase
Refractive Index1.538 to 1.550
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
More from other references
Optical CharacterBiaxial/-
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
More from other references
Birefringence0.010
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
More from other references
DispersionWeak
Michael O’Donoghue, Gems, Sixth Edition (2006)
Colour
Colour (General)Colourless to bluish
Walter Schumann, Gemstones of the world (2001)
More from other references
Causes of ColourBlue (moonstone), Rayleight scattering of light by lamellar structure. Red (sunstone), red lepidocrocite or hematite platelets give the aventurescence
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyTransparent
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
LustreVitreous,Pearly
Walter Schumann, Gemstones of the world (2001) On cleavage surfaces mother-of-pearl lustreMore from other references
Fluorescence & other light emissions
Fluorescence (Long-Wave UV)Pale brownish white, pale brown
Michael O’Donoghue, Gems, Sixth Edition (2006)
Crystallography of Oligoclase
Crystal SystemTriclinic
Walter Schumann, Gemstones of the world (2001)
More from other references
Geological Environment
Where found:As a major part of many rocks, especially igneous rocks such as granites, syenites and pegmatites. Also in intermediate lavas, schists and some amphibolites.
Michael O’Donoghue, Gems, Sixth Edition (2006)
Inclusions in Oligoclase
Red hematite platelets (aventurism) - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 8
Further Information
Mineral information:Oligoclase information at mindat.org
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