mineral

Common opal (rough opalized material)

Hydrated amorphous silica, SiO₂·nH₂O; likely common opal with dark mineral inclusions

AI-generated identification · may be incorrect

Opaque to translucent, cream-gray with brown patches and dark specks; vitreous to waxy luster and conchoidal fracture. Hardness about 5.5–6.5 Mohs; amorphous, with no cleavage. The photo does not show the play-of-color typical of precious opal.

Identified October 11, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich water deposited gel-like silica in rock cavities or fractures, later dehydrating into opal. Opal forms in many geological periods and settings; age cannot be determined from the image.

Uses & applications

Cut or polished for ornamental objects and inexpensive jewelry; rough pieces are mainly collected. Opal has limited industrial use.

Geological facts

Opal is hydrated silica rather than a crystalline quartz mineral; its water content varies. Dark flecks may be inclusions, but their identity cannot be established visually.

Field identification & locations

Look for waxy luster, uneven conchoidal fractures, and translucency at thin edges; these pieces appear to be rough, non-play-of-color opal. Found in silica-rich volcanic and sedimentary settings, notably Australia, Ethiopia, Mexico, and the western United States.