sedimentary
Banded Flint (Polished Stripe Flint)
Silicon Dioxide (SiO2) - variety of Chert
Hardness: 6.5-7 on Mohs scale; Color: alternating bands of gray, tan, brown, and cream; Luster: vitreous to waxy when polished; Crystal structure: Cryptocrystalline; Cleavage: none (conchoidal fracture).
- Hardness
- 6
- Color
- alternating bands of gray, tan, brown, and cream
- Luster
- vitreous to waxy when polished
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: alternating bands of gray, tan, brown, and cream; Luster: vitreous to waxy when polished; Crystal structure: Cryptocrystalline; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the precipitation of silica within sedimentary rock layers, often limestone or chalk. The distinct banding occurs due to rhythmic changes in the environment or water chemistry during mineral deposition, typically dating from the Cretaceous period.
Uses & applications
Primarily used in jewelry as cabochons, pendants, and beads. Historically used for tool-making (stone age) and later for strike-a-lights/fire-starting. Some industrial use as grinding media.
Geological facts
Banded flint is often called 'Striped Flint' or 'Polished Flint.' The most famous variety comes from Poland (Holy Cross Mountains), which was mined as early as the Neolithic period for ritual axes and tools.
Field identification & locations
Identify by its distinct, parallel, rhythmic banding and extreme hardness (cannot be scratched by a steel knife). Look for it in chalk-heavy regions or coastal cliff areas. It is non-porous and feels cool to the touch.
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