Chert (Flint)

Physical Properties

Hardness: 7 (Mohs), Color: Dark grey to black, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline, Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65

Formation & Geological History

Formed from the accumulation of siliceous remains of organisms or precipitation of silica-rich fluids in sedimentary basins. Often found as nodules in limestone or chalk beds.

Uses & Applications

Historically used for stone tools (arrowheads, scrapers) and fire-starting. Used today in road construction, as decorative stone, and in some ceramics.

Geological Facts

Flint is a variety of chert that was essential to prehistoric humans because it breaks into very sharp edges through a process called knapping.

Field Identification & Locations

Identify in the field by its distinctive curved (conchoidal) fracture surfaces and its ability to scratch glass. Found globally in sedimentary environments.

Identified on: 4/27/2026

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