sedimentary

Likely weathered gray flint/chert pebble

Microcrystalline quartz (SiO₂), commonly with chalcedony and minor impurities

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray to bluish-gray, dull to waxy luster, very fine-grained and non-cleavable. The rounded form and surface grooves appear natural weathering or abrasion, though the image is insufficient for certainty.

Identified August 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica replaces sediment or accumulates as biogenic silica in marine or freshwater deposits, commonly during the Paleozoic–Cenozoic. This specimen was likely rounded by stream, beach, or glacial transport.

Uses & applications

Used historically for sharp-edged tools and fire-starting; crushed chert is used as aggregate and road material. Ordinary pebbles have little jewelry or collector value.

Geological facts

Chert fractures conchoidally, producing sharp edges similar to glass. Flint is a dark, commonly nodular variety of chert, while chalcedony is its more translucent fibrous form.

Field identification & locations

Test carefully for a glassy conchoidal fracture and inability to scratch it with a steel knife; quartz should scratch ordinary glass. Common in limestone regions, gravel beds, river channels, and beaches.