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Labradorite

Last updated: April 2026

Displays a spectacular iridescent effect known as labradorescence.

Labradorite has a specific gravity of 2.70 and a refractive index of 1.559–1.573, with a Mohs hardness of 6.0–6.5. It is biaxial +.

Physical & Optical Properties

RI Range1.559–1.573
SG Range2.68–2.75
SG Typical2.70
Hardness (Mohs)6–6.5
Crystal SystemTriclinic
Optic CharacterDR Biaxial (+)
Birefringence0.011
Dispersion0.012
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismWeak
ColorsMulti, Brown, Black, Blue Violet
SpeciesFeldspar
VarietyPlagioclase
MultiBrownBlackBlue Violet

Measured with a polariscope, a refractometer, a hydrostatic balance, a Chelsea filter, a UV torch, a loupe, a darkfield loupe and a spectroscope — step-by-step for each.

Through the refractometer

Labradorite reads 1.560 – 1.571 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 REFRACTIVE INDEX DORotate the stone through a full 360°, reading both edges atevery 45°. SEETwo boundaries, 0.011 apart at their widest separation. MEANSThat gap IS the birefringence. Take max minus min across thewhole rotation — a single position understates it, so onereading is an incomplete one. Computed from gems.json — edge positions are arithmetic, not drawn. RI increases upward; the field above the boundary is the dark one.

Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.

AmazoniteMoonstoneRainbow MoonstoneSunstone

Key Differentiators

Treatments

Measurement Guides

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

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

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Studying for the GIA, FGA, or FEEG practical? Labradorite is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.

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