sedimentary
Chert (often called Flint)
Chert (Cryptocrystalline Quartz, SiO2)
Hardness: 7 (Mohs), Color: Grey, brown, or tan, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.65
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Physical properties
Hardness: 7 (Mohs), Color: Grey, brown, or tan, Luster: Waxy to dull, Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary basins. Most deposits date from the Precambrian to the present, often found as nodules in limestone or chalk.
Uses & applications
Historically used for stone tools and arrowheads. Currently used in road construction, as a source for silicon, and in some jewelry as 'flint nodules'.
Geological facts
Chert's ability to break into extremely sharp edges made it the most important material for early human technology. 'Flint' is specifically a term used for chert found in chalk or marly limestone.
Field identification & locations
Identified by its waxy luster, extreme hardness (scratches glass), and shell-like (conchoidal) fracture pattern. Found globally in sedimentary environments.
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