sedimentary
Chert Pebble (Water-worn Quartz/Chalcedony)
Silicon Dioxide (SiO2)
AI-generated identification · may be incorrectHardness 7 on the Mohs scale, waxy to dull luster, greenish-gray color with quartz veinlets, conchoidal fracture, microcrystalline structure, specific gravity ~2.65.
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Physical properties
Hardness 7 on the Mohs scale, waxy to dull luster, greenish-gray color with quartz veinlets, conchoidal fracture, microcrystalline structure, specific gravity ~2.65.
Formation & geological history
Formed from the accumulation of siliceous oozes or chemical precipitation of silica in ocean or lake beds, followed by diagenesis, erosion, and rounding by river or beach water action.
Uses & applications
Historically used for flintknapping tools; modern uses include landscaping gravel, decorative stone, and educational rock specimens.
Geological facts
Water-rounded chert pebbles are often found on riverbeds and ocean beaches. Due to high microcrystalline quartz content, chert is highly resistant to chemical and physical weathering.
Field identification & locations
Identify by its hardness (scratches glass readily), smooth water-rounded surface, waxy luster, and lack of visible mineral grains. Commonly found on pebble beaches, gravel bars, and glacial till deposits.
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