Chert (often called Flint)

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.

Identified on: 5/3/2026

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