sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Gray, tan, and blue-gray banding; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs scale
Color: Gray, tan, and blue-gray banding
Luster: Waxy to dull

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Gray, tan, and blue-gray banding; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed in marine environments through the precipitation of silica-rich fluids within limestone or chalk beds. Often associated with rhythmic deposition of silica-secreting organisms like diatoms or radiolarians.

Uses & applications

Historically used for stone tools and weapons. Currently used as a silica source in glassmaking, road construction aggregate, and as a decorative landscaping stone.

Geological facts

Flint is a variety of chert that occurs primarily in chalk and marly limestone. It was the most important material for early human technology (Stone Age) due to its ability to produce sharp edges when knapped.

Field identification & locations

Look for a waxy luster and smooth, shell-like (conchoidal) fractures. It will easily scratch glass and often shows sharp, brittle edges where pieces have broken off. Commonly found in riverbeds or within limestone outcrops.