sedimentary
Chert (River Pebble)
Cryptocrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness 6.5-7 (Mohs), waxy to dull luster, conchoidal fracture, opaque to translucent, grey with iron-staining (yellow/brown).
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Physical properties
Hardness 6.5-7 (Mohs), waxy to dull luster, conchoidal fracture, opaque to translucent, grey with iron-staining (yellow/brown).
Formation & geological history
Formed through the accumulation of silica-rich microfossils or chemical precipitation in sedimentary basins; rounded by water erosion in a river environment.
Uses & applications
Used historically for stone tools due to sharp edges; currently used for landscaping, road base, and occasionally as a polishing material for tumble-finish jewelry.
Geological facts
Chert is so durable that it often survives long-distance transport in rivers and glacial till while other rocks break down. It is the parent material for flint.
Field identification & locations
Identify by its waxy texture and shell-like (conchoidal) fracture lines. Commonly found in riverbeds, gravel pits, and coastal beaches.
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