COMPARE GUIDE
Gray SapphireVSGray Spinel
Side-by-side comparison of physical properties, fluorescence, and crystal system — to identify by observation.
Decisive distinctionsDECISIVE
- ◎ is higher in Gray Sapphire, giving a numerical distinguishing point.
- ◎ is higher in Gray Sapphire, giving a numerical distinguishing point.
- ◎ is higher in Gray 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.
Physical propertiesPROPERTIES
| Property | A: Gray Sapphire | B: Gray Spinel | Verdict |
|---|---|---|---|
| Refractive index (RI) | 1.762–1.770 | 1.712–1.736 | A higher |
| Specific gravity (SG) | 3.95–4.03 | 3.58–3.61 | A higher |
| Mohs hardness | 9.0 | 8.0 | A higher |
| Birefringence | 0.008 | — | — |
| Dispersion | — | — | — |
Optics & fluorescenceOPTICS & UV
| Property | A: Gray Sapphire | B: Gray Spinel |
|---|---|---|
| Crystal system | 六方晶系（三方晶系） | 等軸晶系 |
| Pleochroism | 弱（灰・淡灰） | — |
| Chelsea filter | — | — |
| UV (long-wave) | — | — |
| UV (short-wave) | inert | inert |
ObservationOBSERVATION
◆Gray spinel is singly refractive (cubic system) with a single refractometer reading near 1.72; gray sapphire is doubly refractive (hexagonal system) with two readings around 1.76 and weak dichroism.
Color categoriesCATEGORIES
A: Gray Sapphire
Black / gray
B: Gray Spinel
Black / gray
DISTINGUISHING TOOLS · 2 ITEMS
Distinguishing tools
Tools that decide between Gray Sapphire and Gray 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.