Anorthite

Big Photo

Miyake Island, Miyake Subprefecture, Tokyo Metropolis, Japan
0.52 carats
© Stefan Ix

Anorthite is the calcium-rich endmember of the Plagioclase solid solution series, it is a rare compositional variety of Plagioclase.

Anorthite Gemstones by Colour

This table shows the variety of hues this gemstone can be found in. Click on a photo for more information.
 
General Information
A variety or type of:Feldspar
Chemical Formula
CaAl
 
2
Si
 
2
O
 
8
Michael O’Donoghue, Gems, Sixth Edition (2006)
Physical Properties of Anorthite
Mohs Hardness6 to 6.5
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Specific Gravity2.77
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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TenacityBrittle
Michael O’Donoghue, Gems, Sixth Edition (2006)
Cleavage QualityPerfect
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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FractureUneven,Conchoidal
Michael O’Donoghue, Gems, Sixth Edition (2006)
Optical Properties of Anorthite
Refractive Index1.575 to 1.588
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Optical CharacterBiaxial/-
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Birefringence0.013
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Colour
Colour (General)Usually white, grey or colourless but can be pale shades of other colours. Occassionally reddish
Michael O’Donoghue, Gems, Sixth Edition (2006)
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TransparencyTransparent,Translucent
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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LustreVitreous,Dull (Earthy)
Michael O’Donoghue, Gems, Sixth Edition (2006)
Fluorescence & other light emissions
Fluorescence (Long-Wave UV)Cream, pale brown
Michael O’Donoghue, Gems, Sixth Edition (2006)
Crystallography of Anorthite
Crystal SystemTriclinic
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
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Geological Environment
Where found:Anorthite is usually found in contact metamorphic limestones and as a constituent in some basic calc-alkali plutonic rocks and lavas.
Michael O’Donoghue, Gems, Sixth Edition (2006)
Further Information
Mineral information:Anorthite information at mindat.org
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