sedimentary
Chert Nodule (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dark grey to black interior with a light-colored tan/white weathering rind (cortex); Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Dark grey to black interior with a light-colored tan/white weathering rind (cortex); Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed as nodules within sedimentary host rocks like limestone or chalk. It occurs through the precipitation of silica from groundwater that replaces carbonate material, often during the Diagenesis phase.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to sharp edges; currently used for flintlock firearms, fire-starting, and as decorative gravel or landscaping stone.
Geological facts
Flint was one of the most important minerals for early humans, enabling the transition to the Stone Age. When struck against steel, it creates sparks sufficient to ignite tinder.
Field identification & locations
Identify by its smooth, glass-like interior fracture and the thick, chalky outer crust. Common in river beds and chalk cliffs. Field test involves checking the conchoidal (shell-like) fracture pattern.
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