gemstone

Polished fire opal

Opal, hydrated amorphous silica (SiO₂·nH₂O), likely precious fire opal

AI-generated identification · may be incorrect

Mohs hardness 5.5–6.5; translucent orange-red body with vivid play-of-color, vitreous-to-waxy luster, and no cleavage. Opal is noncrystalline (amorphous) and relatively light, with specific gravity about 1.98–2.25.

Identified August 13, 2026More gemstone →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater deposits hydrated silica in cavities and fractures, commonly in volcanic rocks; most gem fire opal formed in Cenozoic volcanic terrains. The image’s intense backlit colors are consistent with polished precious opal, though exact identification requires examination.

Uses & applications

Cut and polished for jewelry and collecting; valuable specimens are used as cabochons, beads, and display stones. It is unsuitable for structural or industrial construction use.

Geological facts

Orange body color comes mainly from iron impurities, while play-of-color results from diffraction by regularly arranged microscopic silica spheres. Heat, sudden temperature changes, and harsh chemicals can cause cracking or crazing.

Field identification & locations

Common sources include Querétaro, Mexico; Ethiopia; Australia; and Brazil. Field clues are low hardness, light weight, waxy appearance, conchoidal fracture, and spectral flashes when moved under directional light; test cautiously because opal can be porous and delicate.