| Property | Alexandrite | Obsidian |
|---|---|---|
| Category | Semi-Precious Gems | Semi-Precious Gems |
| Primary Color | various | black |
| Mohs Hardness | 8.5 | 5.0–5.5 |
| Specific Gravity | 3.69 | 2.35 |
| Refractive Index | 1.739 | 1.45 |
| Crystal System | Orthorhombic | Amorphous |
| Luster | — | Vitreous |
| Chemical Formula | — | — |
| Price Tier | Fine ($500-5,000/ct) | Budget (< $50/ct) |
| Daily Wear | Yes | No |