sedimentary
Chert (River Pebble)
Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: tan to light brown, Luster: waxy to dull, Crystal structure: Microcrystalline/Trigonal, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: tan to light brown, Luster: waxy to dull, Crystal structure: Microcrystalline/Trigonal, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or lacustrine environments. This specimen has been water-worn and smoothed in a river or stream bed.
Uses & applications
Historically used for tool making (arrowheads/scrapers) due to its sharp edges; currently used for landscaping, aggregate in construction, and lapidary tumbling.
Geological facts
Chert is so durable that it often survives long after the surrounding rock has weathered away. It is chemically identical to quartz but contains tiny impurities that give it opaque colors.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and waxy texture. Commonly found in riverbeds, gravel pits, and limestone outcrops worldwide.
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