sedimentary
Chert (Flint / Banded Chalcedony)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness of 7 on the Mohs scale. Colors range from dark gray, bluish-gray, to brownish tones with banding. Exhibits waxy to dull luster, conchoidal fracture, sharp edges when broken, and lacks cleavage.
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Physical properties
Hardness of 7 on the Mohs scale. Colors range from dark gray, bluish-gray, to brownish tones with banding. Exhibits waxy to dull luster, conchoidal fracture, sharp edges when broken, and lacks cleavage.
Formation & geological history
Formed through biochemical or chemical precipitation of silica in marine sedimentary environments, or as secondary nodules replacing calcium carbonate in limestone and chalk deposits.
Uses & applications
Historically used for stone tools, flintknapping arrowheads, and spark-striking fire starters. Modern uses include decorative rock tumbling, gravel aggregate, and gemstone lapidary projects.
Geological facts
Chert was one of the most critical resources for prehistoric humans due to its ability to break into razor-sharp conchoidal flakes, making it ideal for blades, scrapers, and arrowheads.
Field identification & locations
Identified in the field by its hardness (scratches glass), smooth conchoidal fracture surfaces, sharp broken edges, and waxy luster. Widely found in limestone beds, riverbeds, and gravel pits across North America and Europe.
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