sedimentary
Flint / Chert Pebble
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness 7 on Mohs scale; dull to waxy luster; conchoidal fracture; microcrystalline structure with a chalky weathering cortex and yellowish-tan interior.
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Physical properties
Hardness 7 on Mohs scale; dull to waxy luster; conchoidal fracture; microcrystalline structure with a chalky weathering cortex and yellowish-tan interior.
Formation & geological history
Formed as diagenetic silica nodules precipitating within Cretaceous chalk or marine limestone beds, subsequently rounded by fluvial or coastal wave erosion.
Uses & applications
Historically used for prehistoric stone tools, strike-a-light fire starters, and flintlock firearms; modern uses include landscaping gravel and stone polishing.
Geological facts
The distinctive white outer crust, known as a patina or cortex, results from chemical weathering that leaches minerals from the silica matrix.
Field identification & locations
Easily identified on coastal shingle beaches and chalk downlands by its rounded form, hard scratch resistance against steel, and fractured white weathering rind.
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