Fire opal (variety of opal)
gem · uncommon
Quick facts
- Formula
- SiO2·nH2O
- Hardness
- 5–6
- Luster
- vitreous to resinous
- Colors
- yellow to orange to red; may or may not show play‑of‑color
Fire opal is a variety of opal valued for its warm yellow to red body color, classically from Mexico but also found in several other localities. It is hydrous silica composed of submicroscopic spheres; some stones show play‑of‑color, while many are prized purely for their body color.
Look for a resinous to vitreous ‘jelly’ translucency in warm yellow–orange–red cabochons, conchoidal chips with no cleavage, lower hardness than quartz, and an absence of chalcedony banding.
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