sedimentary

Tumbled chert or flint

Microcrystalline quartz (SiO₂), likely brown chert/flint

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; brown to honey-brown, opaque, with a smooth water-worn surface and waxy to dull luster. It has cryptocrystalline quartz structure, no visible cleavage, and conchoidal fracture; specific gravity is about 2.6.

Identified August 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills pores in limestone, chalk, or sediments, commonly during early diagenesis. The rounded shape indicates river, beach, or deliberate tumbling and polishing; its exact geological age cannot be determined from the image.

Uses & applications

Used historically for sharp tools, fire-starting, and construction aggregate; attractive pieces are collected as lapidary material or used in carvings and cabochons.

Geological facts

Chert and flint are compositionally similar; “flint” commonly refers to dark, high-quality chert associated with chalk. Brown coloration usually comes from iron oxides or organic impurities.

Field identification & locations

Look for uniform fine texture, waxy appearance, hardness sufficient to scratch glass, and curved conchoidal chips rather than granular fracture. Common in sedimentary regions, gravel beds, beaches, and glacial deposits.