Alexandrite
Last updated: April 2026
The color-change variety of chrysoberyl, appearing green in daylight and red in incandescent light.
Alexandrite has a specific gravity of 3.73 and a refractive index of 1.746–1.755, with a Mohs hardness of 8.5. 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.
Related: Chrysoberyl Varieties
Key Differentiators
- Dramatic color change
- Strong trichroism
- High hardness
Natural vs. Synthetic
Synthetic alexandrite is commercially available (Flux (Creative Crystals/Inamori), Hydrothermal, Czochralski (pulled), and others). Distinguishing natural from synthetic typically requires microscopic examination of internal features.
- Microscopy (10x loupe): Two- and three-phase fluid inclusions, growth tubes, fine twinning lamellae, irregular stress fractures. No platinum or gas bubbles. Synthetic: Flux: curved flux inclusion clouds, platinum crystal platelets (from growth crucible). Hydrothermal: straight parallel growth lines, two-phase inclusions along growth planes. Czochralski-grown stones show concentric curved growth striae and spherical gas bubbles.
- UV Fluorescence: Inert to weak red-orange under LW and SW. Iron quenches fluorescence. Synthetic: Often stronger, more intense red to orange-red, especially under SW UV. Higher Cr purity and lower Fe content in synthetics enhances response.
- RI / SG: RI 1.746–1.755; SG 3.70–3.78. Note: RI and SG do NOT distinguish natural from synthetic chrysoberyl — use microscopy. Synthetic: Identical range — RI and SG do NOT distinguish natural from synthetic chrysoberyl. Use microscopy.
Loupewise Pro includes a two-phase natural vs. synthetic testing protocol for Alexandrite.
Common Simulants
- Color-change sapphire: Uniaxial negative DR; color shift is typically blue→purple, not green→red; lower dispersion; RI 1.762–1.770.
- Color-change garnet: Isotropic (SR); no dichroism; RI 1.740–1.765 range depending on variety; inert to UV.
- Color-change glass: Isotropic; gas bubbles or swirl marks under loupe; conchoidal fracture; no dichroism.
Commonly Confused With
Commonly confused with: Color-Change Sapphire, Color-Change Garnet, Color Change Glass, Diaspore, Synthetic Color-Change Corundum, Synthetic Spinel.
Treatments
- Fracture Filling (resin/glass)
Related Comparisons
Measurement Guides
Identifying an alexandrite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Alexandrite 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 →