sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs, Color: shades of brown and tan, Luster: waxy to dull, Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7.
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Physical properties
Hardness: 7 Mohs, Color: shades of brown and tan, Luster: waxy to dull, Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine or freshwater environments. This specific specimen has been further shaped and smoothed by fluvial erosion in a riverbed.
Uses & applications
Historically used for stone tools (flintknapping); currently used as river rock for landscaping, road base, and occasionally as a low-cost tumble rock for hobbyists.
Geological facts
Chert is so durable that it often remains as pebbles in rivers long after other rocks have eroded away. It was one of the most important materials for early human technology due to its predictable fracture patterns.
Field identification & locations
Identify by its high hardness (cannot be scratched by a steel blade) and its smooth, waxy texture. Commonly found in riverbeds, gravel pits, and coastal areas.
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