sedimentary

Weathered brown chert or flint pebble

Microcrystalline quartz (SiO₂), likely chert/flint

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; brown to tan, dull-to-waxy luster, very fine-grained cryptocrystalline structure, and no visible cleavage. The rounded shape and small surface cavities indicate natural abrasion and weathering.

Identified September 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica replaces or accumulates within sedimentary deposits, often from microscopic marine organisms, during diagenesis. Its exact age cannot be determined from the image; such pebbles commonly derive from limestone or chalk-bearing formations and later become stream- or beach-rounded.

Uses & applications

Used historically for sharp tools and fire-starting; attractive pieces may be tumbled or used decoratively. This specimen appears common and has little commercial jewelry value.

Geological facts

Chert breaks with a characteristic conchoidal fracture and can produce razor-sharp edges. Flint is generally a dark, dense variety of chert, while brown varieties are often simply called chert.

Field identification & locations

Look for extreme hardness, a smooth waxy surface, absence of cleavage, and conchoidal chips; it should scratch glass but not be scratched by a steel knife. Common as stream, beach, and glacial gravels worldwide.