sedimentary

Polished flint/chert pebble

Microcrystalline quartz (SiO₂), commonly called chert or flint

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; dark gray, brown, tan, and olive colors with waxy to glassy luster, conchoidal fracture, and no visible cleavage. The smooth surface appears naturally water-worn or lightly polished, with possible iron-oxide staining and contrasting veins/inclusions.

Identified August 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica from microscopic marine organisms or groundwater replaces carbonate sediments, commonly in limestone; it may range from Paleozoic to younger deposits. This specimen was likely rounded by stream or beach transport.

Uses & applications

Historically used for sharp stone tools and fire-starting; attractive pieces are used as lapidary stones, ornaments, and collector specimens. Ordinary pebbles have low commercial value.

Geological facts

Its conchoidal fracture can produce exceptionally sharp edges, and flint is a variety of chert traditionally associated with fire-making. The apparent dark patches may be iron/manganese staining or included rock rather than a separate mineral.

Field identification & locations

Identify by its very hard, dense, opaque-to-translucent body, waxy luster, and inability to scratch with a steel knife easily; quartz-rich chert may scratch glass. Common in sedimentary regions, gravel bars, and beaches.