sedimentary
Chert (Flint nodule)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Black, grey, or brown, often with a white limestone chalk cortex; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Black, grey, or brown, often with a white limestone chalk cortex; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through chemical precipitation of silica-rich fluids within sedimentary host rocks, such as limestone or chalk beds. Often contains microfossils from the Cretaceous period.
Uses & applications
Historically used for stone tools (knapping), fire-starting (flint and steel), and landscaping. Occasionally used in jewelry or as a polishing abrasive.
Geological facts
Flint was the primary material used by prehistoric humans to create sharp tools and weapons due to its predictable conchoidal fracture which creates razor-sharp edges.
Field identification & locations
Identify by its characteristic 'shell-like' curved fracture surfaces and its ability to scratch glass. Commonly found in chalk or limestone deposits, particularly in Western Europe and the United States.
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