mineral

Tumbled chalcedony (likely gray/pink chalcedony)

Chalcedony, microcrystalline quartz (SiO₂)

AI-generated identification · may be incorrect

Hardness 6.5–7 Mohs; translucent milky gray, beige, and pink with a waxy-to-glassy luster. It has cryptocrystalline quartz structure, no visible cleavage, conchoidal fracture, and specific gravity about 2.58–2.64.

Identified September 15, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities, fractures, or vesicles in volcanic rocks, commonly as silica gel that crystallizes into microfibrous quartz. Most specimens are Cenozoic to older, depending on the host rock and deposit.

Uses & applications

Used for beads, cabochons, carvings, ornaments, and lapidary material; attractive banded varieties are sold as agate. Common tumbled pieces have modest collector value.

Geological facts

The specimen appears water-worn or machine-tumbled and may contain faint dendritic or cloudy internal patterns. Chalcedony is the material composing agate, onyx, and much jasper.

Field identification & locations

Identify by its smooth waxy surface, translucency, hardness, and lack of cleavage; it should scratch glass but not be scratched by a steel knife. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the western United States.