gemstone

Opal cabochon pendant

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

AI-generated identification · may be incorrect

Pale greenish body with iridescent play-of-color, vitreous-to-waxy luster, and no crystal structure because opal is amorphous. Mohs hardness is about 5.5–6.5; it has conchoidal fracture, low specific gravity (about 2.0–2.2), and is relatively porous and delicate.

Identified August 24, 2026More gemstone →

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Physical properties

Formation & geological history

Opal forms when silica-rich groundwater deposits hydrated silica in cavities, fractures, or sedimentary layers; some varieties form in volcanic cavities. Geological ages range from modern deposits to Cretaceous and younger formations.

Uses & applications

Used primarily in jewelry and ornamental objects; its attractive color flashes make it a popular cabochon gemstone, though it should be protected from impact, heat, and sudden drying.

Geological facts

The rainbow effect is caused by diffraction from regularly arranged microscopic silica spheres, while common opal lacks this effect. The image may also show dyed or treated opal, and exact identification requires magnification and testing.

Field identification & locations

Common sources include Australia, Ethiopia, Mexico, Brazil, and the western United States. Field clues are low density, waxy appearance, curved fracture, and play-of-color; avoid prolonged soaking or harsh chemicals.