Grossular Garnet
Last updated: April 2026
Grossular garnet ranges from colorless (leuco-grossular) to delicate mint green (Merelani mint, Tanzania); the mint variety owes its subtle color to trace vanadium and chromium and is softer in tone than the vivid tsavorite variety of the same species.
Grossular Garnet has a specific gravity of 3.61 and a refractive index of 1.734–1.759, with a Mohs hardness of 6.5–7.5. It is singly refractive.
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
- Colorless (leuco) to delicate mint green — paler, softer green than tsavorite (which is rich saturated green)
- Isotropic SR garnet — no birefringence, no pleochroism; distinguishes from peridot (birefringent) and tourmaline (birefringent)
- Hessonite variety: diagnostic roiled 'heat-wave' / treacle inclusions under loupe — a reliable indicator
- RI 1.734–1.759 — lower than tsavorite (1.740–1.742 typical) and well below andradite/demantoid
- Chelsea filter inert in colorless and mint green (Cr-bearing tsavorite shows red on Chelsea)
Common Simulants
- White Sapphire: Uniaxial DR, birefringent (0.008), RI 1.762–1.770, SG 3.99–4.01. Much higher SG and birefringent — easy separation from isotropic grossular.
- White Topaz: Biaxial DR, RI 1.609–1.643, birefringence 0.008–0.010, SG 3.49–3.57. Lower RI and birefringent — clearly separable from grossular on refractometer.
- Green Tourmaline (mint / Paraiba-type): Uniaxial DR, birefringent (0.014–0.021), RI 1.616–1.650. Birefringence visible under loupe. Lower RI and birefringent vs. isotropic grossular.
- Prehnite (mint green): Biaxial DR, RI 1.616–1.649, SG 2.82–2.94. Much lower RI and SG than grossular; commonly shows botryoidal inclusions.
- Cubic Zirconia (colorless): Isotropic SR, RI over refractometer limit (~2.15), SG 5.6–6.0 — far denser than grossular. Easy separation by SG.
Treatments
- Fracture Filling (very rare)
Measurement Guides
Identifying a grossular garnet? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Grossular Garnet 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 →