sedimentary

Banded Flint (Chert)

Silicon Dioxide (SiO2)

Hardness: 7 Mohs scale; Color: Grey, white, and black bands; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: Grey, white, and black bands
Luster: Waxy to vitreous

Identified June 29, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Grey, white, and black bands; Luster: Waxy to vitreous; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed from silica-rich fluids that precipitated within limestone or chalk beds. Often associated with Cretaceous period formations, where biological silica from sponges or diatoms recrystallized.

Uses & applications

Historically used for tool making (arrowheads/knives) and fire-starting. Currently used in jewelry (cabochons), as an abrasive, and by collectors for its unique banding patterns.

Geological facts

Flint was one of the first materials used by early humans to create technology. Banded varieties, often called 'striped flint,' are specifically sought after for their aesthetic appeal, particularly those from Poland.

Field identification & locations

Identify by its extreme hardness (scratches glass), waxy feel, and sharp shell-like (conchoidal) fractures. Found in chalk pits, gravel deposits, and on beaches in regions like the UK, Poland, and the US Midwest.