Synthetic Color-Change Corundum
Last updated: April 2026
Vanadium-doped synthetic corundum sold as 'alexandrite' in estate jewelry since the mid-20th century. A large proportion of 'alexandrite' in estate rings is this material. Immediately separable from true alexandrite (chrysoberyl) by RI: corundum reads 1.762–1.770; chrysoberyl reads 1.746–1.755. Color change is purple-blue to purple-red, not the green-to-red shift of true alexandrite.
Synthetic Color-Change Corundum has a specific gravity of 4.00 and a refractive index of 1.762–1.770, with a Mohs hardness of 9. It is uniaxial −.
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
- RI 1.762–1.770 — immediately distinguishable from true alexandrite (chrysoberyl) at 1.746–1.755
- SG ~4.00 vs chrysoberyl 3.70–3.78
- Uniaxial negative (DR_U−) vs chrysoberyl biaxial positive (DR_B+)
- Color change: purple-blue→purple-red (not the green→red of true alexandrite)
- Verneuil origin: curved growth striae visible under loupe in transmitted light
Natural vs. Synthetic
Synthetic Color-Change Corundum is commercially available (Flame fusion (Verneuil)). Distinguishing natural from synthetic typically requires microscopic examination of internal features.
- Refractometer: True alexandrite (chrysoberyl): RI 1.746–1.755 Synthetic: Synthetic color-change corundum: RI 1.762–1.770 — conclusive separator
- Polariscope / Optic Figure: True alexandrite: biaxial positive (DR_B+) Synthetic: Synthetic corundum: uniaxial negative (DR_U−)
- Microscopy (Loupe): True alexandrite: natural two-phase fluid inclusions, straight growth planes Synthetic: Verneuil corundum: curved growth striae and gas bubbles visible in transmitted light
Loupewise Pro includes a two-phase natural vs. synthetic testing protocol for Synthetic Color-Change Corundum.
Commonly Confused With
Commonly confused with: Alexandrite.
Measurement Guides
Identifying a synthetic color-change corundum? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Synthetic Color-Change Corundum 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 →