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Kornerupine

Last updated: April 2026

Rare borosilicate mineral from Madagascar, Sri Lanka, and Greenland. Green chromium-bearing variety is the most valued. Strong trichroism is the primary field diagnostic.

Kornerupine has a specific gravity of 3.33 and a refractive index of 1.660–1.699, with a Mohs hardness of 6.5. It is biaxial −.

Physical & Optical Properties

RI Range1.660–1.699
SG Range3.27–3.45
SG Typical3.33
Hardness (Mohs)6.5
Crystal SystemOrthorhombic
Optic CharacterDR Biaxial (−)
Birefringence0.013
Dispersion0.018
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterVariable
PleochroismStrong Trichroic
ColorsGreen, Brown, Yellow Orange
SpeciesKornerupine
GreenBrownYellow Orange

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

Kornerupine varies 1.660 – 1.699 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, 0.013 apart at their widest separation. Thepair drawn here is one specimen: this species is publishedat 1.660 – 1.699, 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.

Key Differentiators

Treatments

Measurement Guides

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

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

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Studying for the GIA, FGA, or FEEG practical? Kornerupine 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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