sedimentary

Tumbled chert or siliceous river pebble

Microcrystalline quartz (SiO₂), likely chert with possible fossil or weathering cavities

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; tan-brown, opaque, with dull to weakly waxy luster and very fine-grained texture. It appears water-worn and polished, with small pits and pale gray-white silica-rich zones; crystal structure is cryptocrystalline, with no visible cleavage.

Identified September 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich fluids replace or cement sediment, commonly during marine sedimentation; its age cannot be determined from the image. The rounded shape indicates later transport and abrasion in a river, beach, or glacial deposit.

Uses & applications

Suitable mainly as a curiosity, teaching specimen, or decorative tumbled stone; ordinary material has little industrial or jewelry value.

Geological facts

Chert is composed of quartz crystals too small to see individually and can fracture with sharp, conchoidal edges. Some surface pits may represent dissolved fossils, gas cavities, or weathering rather than true vesicles.

Field identification & locations

Identify it by its hardness, fine texture, lack of cleavage, and inability to scratch it with a steel knife; it should scratch glass if clean and fresh. Common in limestone regions, gravel beds, and river channels.