mineral

Tumbled chalcedony pebble

Chalcedony, microcrystalline quartz (SiO₂), possibly cream-colored agate

AI-generated identification · may be incorrect

Hardness 6.5–7; cream to tan, with a waxy-to-glassy luster and no visible cleavage. It appears smoothly tumbled and may contain subtle translucent quartz banding or inclusions; specific gravity is about 2.6.

Identified September 4, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures, precipitating microscopic quartz fibers; the source material may range from Cenozoic to older volcanic or sedimentary host rocks. Its rounded shape is human-produced by tumbling.

Uses & applications

Used for beads, cabochons, carvings, ornaments, and inexpensive lapidary specimens; chalcedony is also valued for durability and attractive translucence.

Geological facts

Chalcedony is quartz too fine-grained to show ordinary crystal faces, giving it a smooth, waxy appearance. Color variations may result from iron oxides or other trace impurities.

Field identification & locations

Identify it by its glassy/waxy surface, lack of cleavage, conchoidal fracture, and ability to scratch ordinary glass; a steel file should not scratch it easily. Common sources include Brazil, Uruguay, India, Madagascar, Mexico, and the United States.