Peridot vs Sinhalite: How to Tell Them Apart

Last updated: August 2026

Sinhalite was originally misidentified as a brown variety of peridot and only described as its own gem species in 1952 — and it remains a beloved trap in gemology practicals, a Gem-A FGA classic. The RI ranges overlap (1.665-1.690), both stones are biaxial with strong visible doubling, and the SG ranges touch. The separation rests on the spectroscope: sinhalite's three-band absorption pattern at 452, 475, and 493 nm is essentially unique to it.

Property Comparison

Property Peridot (Olivine) Sinhalite Diagnostic?
RI 1.654 – 1.690 1.665 – 1.712 No
SG 3.27 – 3.48 3.47 – 3.50 No
Hardness 6.5 – 7 6.5 – 7 No
Crystal System Orthorhombic Orthorhombic No
Optic Character DR B+ (biaxial positive) DR B− (biaxial negative) No
Birefringence 0.036 0.038 No
Facet Doubling Extreme Strong No
Fluorescence (LW) Inert Inert No
Pleochroism Weak (yellow-green / green / colorless) Strong trichroic (pale brown / dark brown / greenish brown) Yes
Spectroscope No 452/475/493 nm band set Absorption bands at 452, 475, and 493 nm Yes
Peridot vs Sinhalite: where the ranges part Where the ranges part Peridot and Sinhalite, each recorded property on an axis scaled to the pair Peridot Sinhalite Refractive index overlaps ranges overlap from 1.665 to 1.690 — a reading there decides nothing 1.654–1.690 1.665–1.712 1.651 1.683 1.715 Specific gravity overlaps ranges overlap from 3.47 to 3.48 — a reading there decides nothing 3.27–3.48 3.47–3.50 3.26 3.38 3.51 Birefringence too close to call a gap of 0.002, within the ±0.003 the engine allows a reading — too close to call 0.036 0.038 0.033 0.037 0.041 Ranges as recorded in gems.json for Peridot and Sinhalite; every axis is scaled to the pair, so read the tick labels. A gap wider than the instrument's tolerance (RI ±0.010, SG ±0.10, birefringence ±0.003, as the identification engine applies them) means a single clean reading settles it; an overlap, or a gap inside that tolerance, means that instrument cannot, on its own. Hardness is not drawn: a scratch test damages a cut stone. Birefringence is a single recorded value per material.

The Definitive Tests

  1. Spectroscope — the three-band pattern. Sinhalite shows diagnostic absorption bands at 452, 475, and 493 nm — a pattern essentially unique to sinhalite. This is the definitive call, and it is exactly the kind of spectrum reading the FGA practical rewards.
  2. Refractometer — the upper shadow edge. The ranges overlap between 1.665 and 1.690, but only sinhalite reads above 1.690 (up to 1.712). An upper reading beyond 1.690 rules peridot out. A reading inside the overlap zone means the refractometer alone cannot decide — go to the spectroscope.
  3. SG and pleochroism — supporting evidence. Per the reference data, SG separates at the upper end: sinhalite sits at 3.47-3.50 while peridot spans 3.27-3.48 with a typical value of 3.34, so most peridot weighs in clearly lighter. The dichroscope adds a pointer: sinhalite is strongly trichroic in browns (pale brown / dark brown / greenish brown), while peridot's pleochroism is weak.

Common Mistakes

Frequently Asked Questions

How was sinhalite discovered hiding as peridot?

Sinhalite was originally misidentified as a brown variety of peridot: the two overlap in RI, show similar strong doubling, and occur in similar colors. It was first described as a distinct gem species in 1952, and the separation has been a gemology-exam favorite ever since.

What is the definitive test to separate peridot from sinhalite?

The spectroscope. Sinhalite shows absorption bands at 452, 475, and 493 nm — a pattern essentially unique to it. Supporting evidence: sinhalite's RI can read up to 1.712 (above peridot's 1.690 maximum) and its SG of 3.47-3.50 sits at the very top of peridot's range.

Can specific gravity separate peridot from sinhalite?

Usually, but not always. Sinhalite is 3.47-3.50 while peridot spans 3.27-3.48 (typically 3.34), so the ranges technically touch at the top. A low reading indicates peridot; a reading of 3.47+ favors sinhalite but should be confirmed with the spectroscope.

Identifying a yellow-green or brownish stone? Loupewise walks you through refractometer and spectroscope tests step by step.

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Preparing for the FGA practical? Peridot vs sinhalite is a Gem-A syllabus classic. Loupewise’s timed exam simulators drill exactly this call — separating look-alike stones by their measured properties.

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