sedimentary

Chert (Flint Pebble)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Gray, tan, white; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Gray, tan, white
Luster: Waxy to dull

Identified June 4, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Gray, tan, white; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed as nodules or beds in limestone/chalk through the precipitation of silica from groundwater or accumulating skeletal remains of siliceous organisms (diatoms, radiolarians). Common in many geological ages, especially Cretaceous.

Uses & applications

Historically used for stone tools (arrowheads). Modernly used as road aggregate, in glass making, or tumbled for decor.

Geological facts

Flint is a variety of chert that sparks when struck against steel. This specimen shows a smooth, water-worn texture with a distinct white 'cortex' or weathered outer layer typical of flint nodules.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and waxy, smooth surface. Common in riverbeds and coastal regions near limestone deposits.