mineral

Tumbled or naturally water-worn chalcedony

Chalcedony, microcrystalline quartz (SiO₂)

AI-generated identification · may be incorrect

Typically Mohs hardness 6.5–7, with a waxy to dull luster, translucent gray-blue color, and no visible cleavage; it commonly breaks with a conchoidal fracture. The rounded edges indicate abrasion by water or tumbling.

Identified August 31, 2026More mineral →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater fills cavities and fractures in volcanic rocks, precipitating as microscopic quartz fibers; later weathering releases it as pebbles. Formation ages range from recent alluvial reworking to much older volcanic host-rock deposits.

Uses & applications

Used for cabochons, beads, carvings, ornamental objects, and lapidary work; tougher and more durable than many opaque decorative stones. This small, subdued specimen has modest commercial value.

Geological facts

Gray-blue chalcedony may be informally sold as gray agate, though agate properly implies visible banding or patterned chalcedony. Its fine texture gives it a smooth, almost porcelain-like appearance when polished.

Field identification & locations

Identify it by its glassy-to-waxy surface, hardness sufficient to scratch glass, lack of cleavage, and uniformly fine texture; common sources include volcanic terrains and river gravels worldwide. Exact identification would benefit from a hardness, translucency, and specific-gravity test.