Alexandrite

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Physical & Optical Properties

RI Range1.746–1.755

SG Range3.70–3.78

SG Typical3.73

Hardness (Mohs)8.5

Crystal SystemOrthorhombic

Optic CharacterDR Biaxial (+)

Birefringence0.009

Dispersion0.015

Fluorescence LWModerate Red

Fluorescence SWInert

Chelsea FilterRed

PleochroismStrong Trichroic

ColorsColor Change, Green, Red Pink

SpeciesChrysoberyl

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 1.746–1.763; SG 3.70–3.84. 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.

GemID Pro includes a two-phase natural vs. synthetic testing protocol for Alexandrite.

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Common Simulants

Color-change sapphire: Uniaxial negative DR; color shift is typically blue→purple, not green→red; lower dispersion; RI 1.762–1.778.
Color-change garnet: Isotropic (SR); no dichroism; RI 1.730–1.760 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)

Price Context

Natural — low ($/ct)$5,000

Natural — high ($/ct)$30,000

NotePer carat; fine color-change; exceptional stones can exceed $70,000/ct

Synthetic — low ($/ct)$100

Synthetic — high ($/ct)$500

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

Related Comparisons

Measurement Guides

Identifying an alexandrite? GemID walks through these tests in order — RI, SG, fluorescence, and more.

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