Peridot
Last updated: April 2026
Known for its distinctive olive-green color and strong birefringence.
Peridot has a specific gravity of 3.34 and a refractive index of 1.654–1.690, with a Mohs hardness of 6.5–7.0. It is biaxial +.
Physical & Optical Properties
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
Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.
Key Differentiators
- Very strong facet doubling
- Characteristic 'lily pad' inclusions
- Vitreous luster
Common Simulants
- Green Tourmaline: Tourmaline: uniaxial negative DR; RI 1.624–1.644; SG 3.06; less characteristic doubling than peridot.
- Demantoid Garnet: Demantoid: isotropic SR; no doubling; very high RI (1.888); higher dispersion (fire); SG 3.84.
- Green Glass: Isotropic; no facet doubling; gas bubbles under loupe; conchoidal fracture.
Commonly Confused With
Commonly confused with: Tourmaline, Demantoid Garnet, Glass, Prasiolite, Prehnite, Sinhalite, Synthetic Spinel.
Treatments
- Fracture Filling (rare)
Related Comparisons
Measurement Guides
Identifying a peridot? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Peridot 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 →