Opal vs Quartz
| Property | Opal | Quartz |
|---|---|---|
| Fórmula | SiO2·nH2O | SiO2 |
| Sistema Cristalino | N/A | Trigonal |
| Classe Mineral | N/A | 09 Silicates |
| Dureza Mohs | N/A | 7.0 |
| Cor | N/A | Colorless, white, purple, pink, brown, black |
| Brilho | N/A | Vitreous |
| Traço | N/A | White |
| Transparência | N/A | Transparent |
| Clivagem | N/A | None |
| Fratura | N/A | Conchoidal |
Key Differences
- ◆ Quartz is crystalline SiO2; opal is amorphous hydrated SiO2 (SiO2·nH2O) — same composition, different structure.
- ◆ Precious opal displays play-of-color (opalescence); quartz does not.
- ◆ Opal (hardness 5.5–6.5) is softer than quartz (hardness 7).
- ◆ Opal contains up to 20% water; quartz contains no water.
- ◆ Quartz is stable; opal can dehydrate and crack over time.