COMPARE GUIDE
Natural AlexandriteVSColor Change Spinel
Side-by-side comparison of physical properties, fluorescence, and crystal system — to identify by observation.
- ◎ is higher in Natural Alexandrite, giving a numerical distinguishing point.
- ◎ is higher in Natural Alexandrite, giving a numerical distinguishing point.
- ◎ is higher in Natural Alexandrite, giving a numerical distinguishing point.
Note: properties whose numeric ranges do not overlap are auto-extracted. Both are measurable with a refractometer or heavy-liquid bath.
| Property | A: Natural Alexandrite | B: Color Change Spinel | Verdict |
|---|---|---|---|
| Refractive index (RI) | 1.745–1.755 | 1.712–1.736 | A higher |
| Specific gravity (SG) | 3.71–3.75 | 3.58–3.63 | A higher |
| Mohs hardness | 8.5 | 8.0 | A higher |
| Birefringence | 0.009 | — | — |
| Dispersion | — | — | — |
| Property | A: Natural Alexandrite | B: Color Change Spinel |
|---|---|---|
| Crystal system | 斜方晶系 | 等軸晶系 |
| Pleochroism | 強（緑・赤紫・黄橙） | — |
| Chelsea filter | red | — |
| UV (long-wave) | weak (red) | — |
| UV (short-wave) | weak (red) | inert |
◆Alexandrite (BeAl₂O₄ chrysoberyl coloured by trace Cr³⁺, Mohs 8.5, SG 3.70–3.75, RI 1.746–1.755, doubly refractive biaxial positive, dramatic three-axis showing distinct green-purple-red directional colours, dramatic green-to-red colour change) versus colour-change spinel (Mohs 8, SG 3.58–3.63, RI 1.712–1.736, singly refractive isotropic cubic, no , moderate blue-to-purple colour change). The test on the dichroscope is decisively diagnostic: alexandrite shows dramatic three-axis colour separation (green, purple, red along the three optical axes) while colour-change spinel shows uniform colour from all viewing directions. The polariscope test: alexandrite shows clear under crossed polars while colour-change spinel shows the dark isotropic cross. The colour-change effect itself differs in character: alexandrite's classical 'emerald by day, ruby by night' green-to-red shift versus spinel's typically blue-to-purple or grey-to-purple shift. The specific-gravity difference (3.70–3.75 versus 3.58–3.63) and refractive-index difference (1.746–1.755 versus 1.712–1.736) are diagnostic. Alexandrite commands substantially higher prices ($10,000–$60,000+ per carat for fine clean Russian Ural or Brazilian Hematita material) versus colour-change spinel ($500–$15,000 per carat).
Distinguishing tools
Tools that decide between Natural Alexandrite and Color Change Spinel in practice.
Note: this page is auto-generated from published GIA / CGL reference values. Individual stones, treatments, and synthetics may fall outside these ranges. For a definitive identification, consult an accredited gem laboratory.