Synthetic Color-Change Corundum

Key Differentiators

• RI 1.762–1.778 — 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 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 1.762–1.778 — 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

Commonly Confused With

Commonly confused with: Alexandrite.

Price Context

Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.

About Synthetic Color-Change Corundum

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 1.762–1.778; chrysoberyl reads 1.746–1.755. Color change is purple-blue to purple-red, not the green-to-red shift of true alexandrite.