sedimentary

Chert (Flint)

Chert (SiO2)

Hardness: 7 Mohs; Color: Black, grey, or brown; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs
Color: Black, grey, or brown
Luster: Dull to waxy

Identified June 7, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Black, grey, or brown; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed as nodules or beds in sedimentary rocks through the accumulation of silica-rich organic remains or chemical precipitation from groundwater. Most common in Carboniferous or Cretaceous limestone formations.

Uses & applications

Historically used for stone tools and weapons; currently used for road surfacing, as grinding media, and for starting fires (flint and steel).

Geological facts

Commonly known as ‘flint’ when found in chalk or limestone; it was the primary material for prehistoric hand axes due to its ability to hold a sharp edge.

Field identification & locations

Identify by its waxy luster, extreme hardness (scratches glass), and characteristic shell-like (conchoidal) fractures. Found worldwide in limestone districts.