sedimentary
Chert (variant Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: Dull gray to grayish-brown, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline microquartz, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Dull gray to grayish-brown, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline microquartz, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds. Geological age can range from Precambrian to Holocene.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to conchoidal fracturing. Modernly used as a road aggregate, in jewelry (tumbled stones), and as 'flint' in fire-starting strike kits.
Geological facts
Chert and flint were among the first materials used by early humans for tool-making. Because it breaks with very sharp edges, it provides an insight into the stone-age technological transition. It can spark when struck against steel.
Field identification & locations
Identify in the field by its characteristic smooth, curved (conchoidal) breaks that look like a sea shell pattern. It will not be scratched by a steel knife. Commonly found in riverbeds, glacial tills, and embedded in limestone cliffs.
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