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.
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
Key Differentiators
- Strong trichroism (colorless / brown-yellow / green) — visible to naked eye in some specimens
- Biaxial negative — separates from tourmaline (uniaxial negative)
- Higher SG (3.27–3.45) than tourmaline (3.00–3.26)
- Rare: most misidentified 'kornerupine' at gem shows is tourmaline
Treatments
- Metallic Coating (documented by GIA)
Measurement Guides
Identifying a kornerupine? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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