← Back to Reference Database RI Chart SG Chart Fluorescence Hardness

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.

Sunstone has a specific gravity of 2.63 and a refractive index of 1.537–1.572, with a Mohs hardness of 6.0–6.5. It is biaxial −.

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)
Yellow OrangeRed PinkColorlessGreen

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

Sunstone varies 1.537 – 1.572 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, 0.010 apart at their widest separation. Thepair drawn here is one specimen: this species is publishedat 1.537 – 1.572, and the two edges slide together anywhereacross it, between the dashed marks. MEANSThat gap IS the birefringence — and it is the stable part.Where the pair sits varies by 3 printed divisions from stoneto stone, so the gap identifies and the position onlynarrows. Take max minus min across the whole rotation; asingle position understates it. 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.

AmazoniteLabradoriteMoonstoneRainbow Moonstone

Key Differentiators

Treatments

Measurement Guides

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

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

Try Loupewise Free →

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

Practice exams →