mineral

Tumbled chalcedony (likely pale agate or common opal)

Microcrystalline quartz, SiO₂; possibly hydrated silica, SiO₂·nH₂O, if opal

AI-generated identification · may be incorrect

Creamy white to tan, translucent, waxy-to-glassy luster, and rounded tumbled form; chalcedony hardness is about 6.5–7 Mohs, while opal is 5.5–6.5. No visible cleavage; cryptocrystalline or amorphous structure.

Identified September 15, 2026More mineral →

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Physical properties

Formation & geological history

Silica-rich groundwater deposited silica in cavities or fractures of volcanic rock, generally during the Cenozoic or earlier; tumbling is human processing. The specimen’s uniform pale appearance prevents definitive separation of chalcedony from common opal by photo alone.

Uses & applications

Used as an inexpensive lapidary stone, cabochon, bead, craft material, and collector specimen; non-gem-quality material has little industrial importance.

Geological facts

A steel file or quartz scratch test can help distinguish it: chalcedony resists scratching better than glass, whereas opal is softer. Agate varieties may show banding, but none is clearly visible here.

Field identification & locations

Common sources include Brazil, Uruguay, Madagascar, India, Mexico, and the western United States. Check translucency, waxy luster, conchoidal fracture, and hardness; avoid confusing it with glass or ceramic.