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Oligoclase is a member of the plagioclase feldspar group. Two oligoclase varieties, sunstone and moonstone, are prized for their phenomenal optical properties.

Oligoclase Polished
Oligoclase Classification
Common Name Oligoclase
Species Feldspar
Oligoclase Optical Properties
Transparency Translucent - Opaque
Refractive Index 1.539-1.547
Birefringence 0.007-0.01
Optic Character Biaxial
Optic Sign Negative
Polariscope Reaction Aggregate (AGG), Doubly Refractive (DR)
Fluorescence SWUV: Inert
LWUV: Inert
Pleochroism Unobservable
Oligoclase Characteristic Physical Properties
Hardness 6-6.5
Specific Gravity 2.620-2.670 Typical:2.650
Toughness Poor
Inclusions Oligoclase feldspar has parallel closely spaced twinning planes. Transparent material might show eye-visible iridescent platelets.
Luster Vitreous
Stability Good
Fracture Uneven, Splintery
Cleavage Perfect, in two directions
Oligoclase Chemistry & Crystallography
Chemical Name calcium or sodium silicate
Chemical Formula NaAlSi3O8 or CaAl2Si2O8
Crystal System Triclinic
Chemistry Classification Silicate

Oligoclase Colors

  • Colorless Oligoclase Colorless
  • Yellow Oligoclase Yellow
  • Green Oligoclase Green
  • White Oligoclase White
  • Gray Oligoclase Gray
  • Orange Oligoclase Orange
  • Brown Oligoclase Brown

Countries of Origin

Brazil; Kenya

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Tim Matthews


Tim Matthews

Tim Matthews is President and Chief Executive Officer of Jewelry Television® (JTV), as well as a member of the company's Board of Directors. He oversees and leads all aspects of the company's powerful omni-digital retail platform that uniquely specializes in fine jewelry and gemstones. His passion for business and gemstones has led him to become a recognized expert in the field of gemology. He is a life member of the Gemmological Association of Great Britain (Gem-A) and has earned Gem-A's highest degrees, the Gemmology (FGA) and Diamond (DGA) diplomas. He is also a Graduate Gemologist (GG) of the Gemological Institute of America (GIA) and has also completed GIA's Graduate Diplomas in Diamonds, Colored Stones and Pearls. Under his leadership, JTV has become the leader in the sourcing and selling of color gemstones and jewelry.

This page was created on June 27, 2014.

This page was last edited on October 24, 2019.