| Property | Black Opal | Tiger's Eye |
|---|---|---|
| Category | Semi-Precious Gems | Semi-Precious Gems |
| Primary Color | white | various |
| Mohs Hardness | 6.0–6.5 | 6.5–7.0 |
| Specific Gravity | 1.97 | 2.58 |
| Refractive Index | 1.37 | 1.534 |
| Crystal System | Amorphous | Trigonal |
| Luster | Vitreous | Vitreous |
| Chemical Formula | — | — |
| Price Tier | Moderate ($50-500/ct) | Moderate ($50-500/ct) |
| Daily Wear | No | No |