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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.

Moonstone has a specific gravity of 2.58 and a refractive index of 1.518–1.526, with a Mohs hardness of 6.0–6.5. It is biaxial −.

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
ColorlessYellow OrangeBrownGreenRed Pink

AmazoniteLabradoriteRainbow MoonstoneSunstone

Key Differentiators

Commonly Confused With

Commonly confused with: Rainbow Moonstone.

Treatments

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

How to Identify a GemstoneHow to Measure Specific GravityHow to Use a RefractometerUV Fluorescence Testing

Identifying a moonstone? GemID walks through these tests in order — RI, SG, fluorescence, and more.

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Studying for the GIA, FGA, or FEEG practical? Moonstone is one of the 130 species in GemID’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.

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