mineral

Tumbled chalcedony (likely agate)

Microcrystalline quartz, SiO₂; chalcedony with possible agate banding

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; typically white, cream, gray, and pale pink with waxy to vitreous luster. Quartz has a trigonal crystal structure, but chalcedony is composed of microscopic intergrowths and lacks visible cleavage; conchoidal fracture is typical.

Identified September 18, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, depositing fibrous quartz in layers over time. The specimen is likely naturally ancient, commonly associated with Cenozoic to Paleozoic volcanic terrains, though its precise age cannot be determined visually.

Uses & applications

Used as a lapidary stone for tumbled pieces, cabochons, carvings, beads, and decorative objects; attractive banded material may be used in jewelry.

Geological facts

The rounded shape and polished-looking surface indicate human tumbling or natural water abrasion. Its cloudy appearance may result from inclusions, microscopic pores, or iron staining.

Field identification & locations

Identify by its waxy feel, translucency, conchoidal fracture, and inability to scratch with a steel knife; it should scratch glass. Common sources include Brazil, Uruguay, Mexico, India, Madagascar, and the western United States.