Chert (including Flint and Jasper variants)

Physical Properties

Hardness: 7 on Mohs scale; Color: variety of grays, blacks, and browns; Luster: waxy to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Formation & Geological History

Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.

Uses & Applications

Historically used for stone tools and weapons (arrowheads); currently used in road construction, as gemstones when colorful (jasper), and for starting fires (flint).

Geological Facts

Chert was one of the most important materials for early humans because its conchoidal fracture creates extremely sharp edges; it is also highly resistant to chemical weathering.

Field Identification & Locations

Identify in the field by checking for a smooth, glass-like fracture (conchoidal), high hardness (cannot be scratched by a steel knife), and a waxy texture. Commonly found as nodules in limestone or chalk beds.

Identified on: 4/26/2026

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