sedimentary

Chert

Chert (SiO2)

Hardness: 7 Mohs; Color: White to off-white/beige; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 7 Mohs
Color: White to off-white/beige
Luster: Dull to waxy

Identified July 21, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: White to off-white/beige; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed by the precipitation of silica in sedimentary environments, often replacing carbonate materials or through the accumulation of siliceous microfossils like radiolaria on the seafloor. This specimen exhibits the characteristic sharp, shell-like fracture lines.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as road aggregate, in glass manufacturing, and as decorative stone.

Geological facts

Chert is essentially the same material as flint, but the term flint is usually reserved for dark varieties found in chalk beds. It is extremely chemically stable and resistant to weathering.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel) and smooth, curved conchoidal fractures. Commonly found in limestone or dolomite beds as nodules or layers.