Moonstone
Last updated: April 2026
Characterized by a billowy, bluish-white light effect called adularescence. IMPORTANT: "Rainbow moonstone" is a trade name for white labradorite (plagioclase feldspar), NOT orthoclase moonstone. Distinguish by RI: labradorite reads above 1.559; true moonstone reads 1.518–1.526 on the refractometer. One of the most commonly misidentified feldspars in consumer jewelry.
Physical & Optical Properties
RI Range1.518–1.526
SG Range2.56–2.59
SG Typical2.58
Hardness (Mohs)6–6.5
Crystal SystemMonoclinic
Optic CharacterDR Biaxial (−)
Birefringence0.008
Dispersion0.012
Fluorescence LWWeak blue
Fluorescence SWInert
Chelsea FilterInert
PleochroismNone
ColorsColorless, Yellow Orange, Brown, Green, Red Pink
SpeciesFeldspar
VarietyOrthoclase
Related: Feldspar Varieties
Key Differentiators
- Adularescence (schiller)
- Two cleavage directions at 90 degrees
- Typical RI and SG
Commonly Confused With
Commonly confused with: Rainbow Moonstone.
Treatments
- Fracture Filling (occasional)
- Surface Coating / Bleaching (inferior material)
Price Context
Natural — low ($/ct)$20
Natural — high ($/ct)$200
NotePer carat; fine blue-white adularescence on a colorless body commands premium; Sri Lankan material top quality
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a moonstone? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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