sedimentary

Flint (or Chert)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, black, or brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, black, or brown
Luster: Waxy to vitreous

Identified March 8, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, black, or brown; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed as nodules in sedimentary rocks like chalk or marine limestone. It originates from the accumulation of silica-rich organic remains (like sponge spicules or radiolaria) that dissolve and reprecipitate during diagenesis.

Uses & applications

History's most important stone for tool-making (arrowheads, knives). Used today in ceramics, as an abrasive, in road construction, and occasionally for 'flintlock' ignition mechanisms. Collectors value worked artifacts and unique nodules.

Geological facts

Flint was the first 'commodity' traded by humans. Because it breaks with incredibly sharp edges, surgical scalpels made of flint are sharper than high-quality steel blades on a microscopic level.

Field identification & locations

Identify by its 'waxy' texture and conchoidal (shell-like) fracture patterns. It often has a white outer 'cortex'. Found globally, notably on beaches in the UK, France, and Northern Europe, and in limestone regions of North America.