sedimentary
Chert (River Pebble)
Microcrystalline silica (SiO2)
Hardness: 7 (Mohs scale), Color: Brownish-gray with white patination, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal
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Physical properties
Hardness: 7 (Mohs scale), Color: Brownish-gray with white patination, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal
Formation & geological history
Forms from the accumulation of siliceous remains of marine organisms or through chemical precipitation in groundwater; shaped and rounded by river erosion.
Uses & applications
Historically used for stone tools (arrowheads); currently used for road aggregate, landscaping, or as a common collector's find.
Geological facts
Chert is so hard it can strike sparks from steel. Flint is a high-quality variety of chert. This specific specimen shows a 'heavy patina' or weathering rind common in alluvial deposits.
Field identification & locations
Identify by its hardness (cannot be scratched by a steel knife) and its smooth, water-worn surface. Commonly found in riverbeds and glacial tills worldwide.
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