Sunstone
Last updated: April 2026
A plagioclase feldspar (typically oligoclase or andesine) displaying aventurescence — a metallic shimmering or spangling caused by flat metallic inclusions. Oregon sunstone (often andesine-labradorite, RI up to ~1.568) may show red, green, or bicolor zones. Indian sunstone (oligoclase) shows a golden glitter from hematite/goethite platelets. Copper-bearing Oregon sunstones are natural and untreated.
Physical & Optical Properties
RI Range1.537–1.572
SG Range2.62–2.65
SG Typical2.63
Hardness (Mohs)6–6.5
Crystal SystemTriclinic
Optic CharacterDR Biaxial (−)
Birefringence0.010
Dispersion0.012
Fluorescence LWWeak orange
Fluorescence SWInert
Chelsea FilterInert
PleochroismWeak
ColorsYellow Orange, Red Pink, Colorless, Green
SpeciesFeldspar
VarietyPlagioclase (Oligoclase / Andesine)
Related: Feldspar Varieties
Key Differentiators
- Aventurescence (schiller) — metallic spangling from copper or hematite/goethite platelets
- Feldspar RI (1.537–1.572) and SG (2.62–2.65)
- Biaxial positive — distinct from uniaxial gems
Treatments
- Copper Diffusion ('Congo Sunstone' / 'Red Labradorite')
Price Context
Natural — low ($/ct)$10
Natural — high ($/ct)$300
NotePer carat; Oregon sunstone (bicolor, deep red, or large copper inclusions) commands significant premium; Indian material more common and less expensive
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a sunstone? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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