sedimentary
Chert (Flint)
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 (Mohs scale); Color: Black to dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Black to dark grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Black to dark grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from silica-saturated fluids in marine environments. Often found as nodules in limestone or chalk beds.
Uses & applications
Historically used for stone tools and weapons due to sharp edges when fractured. Modernly used in construction aggregate, road surfacing, and as a strike-stone for fire-making.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. It was the primary material for the Neolithic 'Flint Mines' and was essential for flintlock firearms in the 17th-19th centuries.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture, extreme hardness (scratches glass), and waxy texture. Commonly found in riverbeds or eroding out of sedimentary rock faces.
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