gemstone

Opal cabochon

Hydrated amorphous silica, SiO₂·nH₂O; likely common or synthetic opal

AI-generated identification · may be incorrect

Translucent, polished oval with green play-of-color; vitreous to waxy luster and no crystal cleavage. Hardness is approximately 5.5–6.5 Mohs; specific gravity about 1.98–2.25.

Identified September 2, 2026More gemstone →

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Physical properties

Translucent, polished oval with green play-of-color; vitreous to waxy luster and no crystal cleavage. Hardness is approximately 5.5–6.5 Mohs; specific gravity about 1.98–2.25.

Formation & geological history

Opal forms when silica-rich groundwater deposits hydrated silica in cavities and fractures, commonly in volcanic or sedimentary rocks. Its age depends on locality, generally ranging from Cenozoic to younger deposits; the image may also show laboratory-created opal.

Uses & applications

Used primarily in jewelry and ornamental cabochons; industrial silica opal has limited applications. Fine natural precious opal can be valuable, while synthetic or common opal is inexpensive.

Geological facts

The green flashes are caused by diffraction from ordered silica spheres, producing opalescence rather than ordinary surface reflection. Opal contains water and can craze or crack with drying, heat, or sudden temperature changes.

Field identification & locations

Identify by its rounded cabochon cut, translucent body, and shifting spectral flashes under directional light; natural material may show irregular color patches and inclusions. Major sources include Australia, Ethiopia, Mexico, and Nevada.