COMPARE GUIDE
Black SpinelVSBlack Star Sapphire
Side-by-side comparison of physical properties, fluorescence, and crystal system — to identify by observation.
- ◎ is higher in Black Star Sapphire, giving a numerical distinguishing point.
- ◎ is higher in Black Star Sapphire, giving a numerical distinguishing point.
- ◎ is higher in Black Star Sapphire, 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: Black Spinel | B: Black Star Sapphire | Verdict |
|---|---|---|---|
| Refractive index (RI) | 1.712–1.736 | 1.762–1.770 | B higher |
| Specific gravity (SG) | 3.58–3.90 | 3.95–4.05 | B higher |
| Mohs hardness | 8.0 | 9.0 | B higher |
| Birefringence | — | 0.008 | — |
| Dispersion | — | — | — |
| Property | A: Black Spinel | B: Black Star Sapphire |
|---|---|---|
| Crystal system | 等軸晶系 | 六方晶系（三方晶系） |
| Pleochroism | — | — |
| Chelsea filter | — | — |
| UV (long-wave) | — | — |
| UV (short-wave) | inert | inert |
◆Black spinel is singly refractive (RI 1.71–1.72), SG 3.58–3.61, and shows no asterism — it is a flat, opaque black stone without star rays. Black star sapphire is doubly refractive (RI 1.76–1.77), SG 4.00, and shows a six-rayed star under a point light.
Distinguishing tools
Tools that decide between Black Spinel and Black Star Sapphire 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.