mineral

Tumbled chalcedony (likely agate or common quartz)

Microcrystalline quartz, SiO₂; possible iron-oxide staining

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; blue-gray to gray, waxy-to-dull luster, translucent edges, cryptocrystalline structure, and no visible cleavage. The rounded shape and smooth surface indicate tumbling or natural water abrasion.

Identified August 16, 2026More mineral →

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Physical properties

Formation & geological history

Chalcedony forms when silica-rich groundwater fills cavities and fractures, commonly in volcanic rocks; iron-bearing fluids can create the rusty seam. Precise geological age and locality cannot be determined from the photograph.

Uses & applications

Used for inexpensive cabochons, beads, carvings, lapidary pieces, and decorative objects; agate varieties are also collected and used in ornaments.

Geological facts

Chalcedony is quartz composed of extremely fine intergrown crystals, making individual crystals difficult to see. The specimen may be a naturally rounded pebble rather than a deliberately tumbled stone.

Field identification & locations

Look for its waxy appearance, translucency, quartz hardness, and conchoidal fracture; it should scratch ordinary glass but not be scratched by a steel knife. Common in volcanic terrains, river gravels, and silica-rich cavities worldwide.