Sunstone Feldspar

Oligoclase is really a types of plagioclase feldspar. The range utilized in jewellery is known as sunstone or, less commonly, aventurine feldspar. It's reflective inclusions of red, orange, or green platy crystals, which provide a metallic glitter. Sunstone might be faceted or carved - frequently cabochons.
Sunstone happens in metamorphic and igneous rocks in Norway, the United States, India, the first kind USSR, and Canada.

Properties

Chemical Composition: 

Aluminum silicate of potassium, sodium and calcium. KAlSi₃O₈. Isomorphous series made up of Albite (Na), Oligoclase, Andesine, Labradorite, Bytownite and Anorthite (Ca) where the two end member are NaAlSi₃O₈ and CaAl₂Si₂O₈.

Classification / Type: 

-

Colors / Varieties: 

Plagioclase:

• Albite: Moonstone (orthoclase-albite)
• Labradorite: Transparent (white, grey, yellow); Phenomena: chatoyancy, asterism, play of color i.e., labradorescence); Spectrolite: dark background with play of color.
• Oligoclase: Sunstone: Phenomena: aventurescent, chatoyancy

Crystal System / Forms: 

Triclinic System

Hardness: 

6.5

Specific Gravity: 

2.63 - 2.72

Cleavage / Fracture: 

Easy 2 directional / Uneven.

Optic Character: 

Anisotropic, D.R.; Biaxial negative

Lustre: 

Vitreous

Refractive Index / Birefringence: 

1.542 - 1.549 / 0.00

Pleochroism: 

Not common.

Dispersion: 

0.012

Magnification: 

Platelets of goethite, copper, hematite, fingerprints and crystal inclusions.

U.V. Fluorescence: 

Variable.

Spectrum: 

Not characteristic.

Cause of Color: 

Aventurescent effect due to reflections from metallic inclusion like hematite, goethite or copper.

Treatment (Enhancement): 

None.

Specific Tests & Remarks: 

-

Synthesis: 

None.

Simulants (with key separation tests): 

Sunstone simulated by aventurine quartz (structure), goldstone glass (inclusions).

Geological Occurrence: 

Igneous rocks, pegmatite.

Sources: 

U.S.A. (Oregon), India, Kenya, Norway, Russia.

Cuts & Uses: 

Facetted, cabochon, beads and carving.