$Chalcedony (likely flint/chert), possibly an impact-fractured pebble (Microcrystalline quartz, SiO₂; chalcedony/chert) — sedimentary$

sedimentary

Chalcedony (likely flint/chert), possibly an impact-fractured pebble

Microcrystalline quartz, SiO₂; chalcedony/chert

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray-brown, waxy to dull luster, cryptocrystalline structure, no visible cleavage, and conchoidal fracture. The smooth rounded form and dark translucent-looking interior may reflect natural weathering or polishing, while the triangular markings could be fracture surfaces or inclusions.

Identified August 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich groundwater replaces or precipitates within sediment, commonly in limestone or marine sediments; ages range from Precambrian to recent. The specimen appears water-worn and may have been tumbled or naturally rounded.

Uses & applications

Used for stone tools, abrasives, ornamental objects, cabochons, and beads; attractive patterned pieces have modest lapidary value.

Geological facts

Chert and flint are compositionally similar varieties of microcrystalline quartz, with flint traditionally referring to dark, high-quality chert. Conchoidal fracture can produce very sharp edges.

Field identification & locations

Common in river gravels, limestone regions, and glacial deposits. Test carefully with a steel file or streak-free scratch test: it should resist scratching and leave no colored streak; identification from the photo is not definitive.