mineral

Fire Opal in Host Rock

Amorphous Hydrous Silica (SiO2·nH2O)

Hardness: 5.5-6.5; Color: Milky white, orange, and blue-green flashes (play-of-color); Luster: Vitreous to waxy; Structure: Amorphous; Specific Gravity: 1.9-2.3

Hardness: 5
Color: Milky white, orange, and blue-green flashes (play-of-color)
Luster: Vitreous to waxy

Identified May 24, 2026More mineral →

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Physical properties

Hardness: 5.5-6.5; Color: Milky white, orange, and blue-green flashes (play-of-color); Luster: Vitreous to waxy; Structure: Amorphous; Specific Gravity: 1.9-2.3

Formation & geological history

Formed from silica-rich water seeping into cracks and cavities in volcanic host rock (often rhyolite or basalt) during the Cenozoic era.

Uses & applications

Used primarily in jewelry as gemstones, mineral collecting, and metaphysical ornamental pieces.

Geological facts

Opals contain between 3% and 21% water by weight. Precious opal is unique for its diffraction of light, which creates a characteristic rainbow play-of-color.

Field identification & locations

Identify by looking for waxy or glassy patches within a duller volcanic matrix; wet the stone to reveal hidden colors. Common in Virgin Valley (Nevada), Mexico, and Australia.

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