sedimentary

Chert (Flint)

Cryptocrystalline Quartz (SiO2)

Hardness: 7.0, Color: tan, brown, or grey with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Hardness: 7
Color: tan, brown, or grey with waxy luster

Identified June 22, 2026More sedimentary →

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Physical properties

Hardness: 7.0, Color: tan, brown, or grey with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Formation & geological history

Formed in sedimentary environments from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater.

Uses & applications

Historically used for stone tools and fire-starting. Currently used in road surfacing, as grinding media, and occasionally as decorative landscaping stone.

Geological facts

Flint is a variety of chert that produced sparks when struck against steel, making it essential for early firearms like flintlocks. It breaks with extremely sharp edges, sharper than a surgeon's scalpel.

Field identification & locations

Identify by its smooth, waxy surface and characteristic shell-like (conchoidal) fractures. Found globally in limestone and chalk beds, particularly in the UK, USA, and France.