sedimentary
Flint / Chert
Silicon Dioxide (SiO2)
Hardness of 7 on the Mohs scale; waxy to dull luster; microcrystalline or cryptocrystalline structure; sharp, conchoidal fracture edges; color ranges from yellowish-brown, grey, to dark charcoal and black.
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Physical properties
Hardness of 7 on the Mohs scale; waxy to dull luster; microcrystalline or cryptocrystalline structure; sharp, conchoidal fracture edges; color ranges from yellowish-brown, grey, to dark charcoal and black.
Formation & geological history
Formed through chemical sedimentary processes, often by the accumulation of siliceous organism remains (like sponges or radiolarians) in marine chalk or limestone beds during diagenesis.
Uses & applications
Historically used for prehistoric tools, arrowheads, and spark-striking fire starters. Modernly used in road construction, ceramics, and as lapidary decorative specimens.
Geological facts
Flint produces sparks when struck against iron or steel due to tiny iron particles igniting upon chipping. It was one of the first minerals extensively mined by prehistoric humans in Neolithic flint mines.
Field identification & locations
Look for smooth, waxy surfaces with razor-sharp conchoidal fractures and a soft, chalky white outer rind (cortex). Widely found in chalk outcrops, coastal beaches, and limestone riverbeds across the UK, Europe, and North America.
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