sedimentary

Chert (Flint)

Chert (Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Black to dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Hardness: 7 (Mohs scale)
Color: Black to dark grey
Luster: Waxy to dull

Identified June 4, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Black to dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & geological history

Formed via the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from silica-saturated fluids in marine environments. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons due to sharp edges when fractured. Modernly used in construction aggregate, road surfacing, and as a strike-stone for fire-making.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. It was the primary material for the Neolithic 'Flint Mines' and was essential for flintlock firearms in the 17th-19th centuries.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture, extreme hardness (scratches glass), and waxy texture. Commonly found in riverbeds or eroding out of sedimentary rock faces.