Precious opal
Varietyof Opal
Precious opal is opal showing play-of-color. As a variety of Opal, it shares that species' composition (SiO2·nH2O), crystal structure, and hardness; the distinction is the appearance defined above.
About Opal
Full reference data — crystallography, X-ray diffraction, and cited physical properties — is on the Opal species page.
| Formula | SiO2·nH2O |
|---|---|
| Streak | white |