sedimentary

Chert (Flint)

Cryptocrystalline Quartz (SiO2)

Hardness: 7 Mohs; Color: Tan, brown, or gray; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs
Color: Tan, brown, or gray
Luster: Dull to waxy

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Tan, brown, or gray; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed in sedimentary environments as nodules or layered deposits when silica-rich fluids replace carbonate material or precipitate from groundwater. This specimen appears to be of the 'common chert' variety.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to conchoidal fracturing. Modernly used in construction aggregate and as a specimen for geological education.

Geological facts

Chert has been used by humans for over two million years to create sharp cutting tools. It can spark when struck against steel, which is why the dark variety (flint) was crucial for early firearms.

Field identification & locations

Identify in the field by its sharp, glass-like edges where broken and its ability to scratch glass. It often has a weathered white or tan 'rind' and a smoother, denser interior.