Sinhalite
Last updated: April 2026
Sinhalite is a rare borate mineral first described as a gem species in 1952 (originally misidentified as a brown peridot variety). It is still frequently misidentified as peridot, brown tourmaline, or zircon. The diagnostic triple absorption bands at 452, 475, and 493 nm in the spectroscope (Anderson 1990) are the definitive test. The high birefringence (0.038) produces strong facet doubling visible under 10× loupe.
Physical & Optical Properties
RI Range1.665–1.712
SG Range3.47–3.50
SG Typical3.48
Hardness (Mohs)6.5–7
Crystal SystemOrthorhombic
Optic CharacterDR Biaxial (−)
Birefringence0.038
Dispersion0.018
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismStrong Trichroic
ColorsBrown, Yellow Orange, Green
SpeciesSinhalite (MgAlBO₄)
Key Differentiators
- Diagnostic spectroscope absorption bands at 452, 475, and 493 nm — essentially unique to sinhalite
- Strong facet doubling visible under 10× loupe (birefringence 0.038)
- RI 1.665–1.712 with biaxial negative optic sign
- SG 3.47–3.50 — heavier than peridot (3.28–3.48)
- Distinct trichroism: pale brown / dark brown / greenish brown
Commonly Confused With
Commonly confused with: Peridot.
Price Context
Natural — low ($/ct)$50
Natural — high ($/ct)$500
NotePer carat; rare collector gem; fine brown to golden stones from Sri Lanka; small market
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a sinhalite? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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