sedimentary
Chert (Flint Nodules)
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, black, or brown interior with a white calcareous cortex; Luster: Waxy to vitreous; Structure: Cryptocrystalline/microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, black, or brown interior with a white calcareous cortex; Luster: Waxy to vitreous; Structure: Cryptocrystalline/microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the precipitation of silica from seawater or the replacement of limestone/chalk by silica. They often occur in Cretaceous or Jurassic chalk beds as nodules or layers.
Uses & applications
Historically used for stone tools (knapping) and fire-starting. Today used in construction aggregates, road beds, and occasionally as decorative landscaping stone.
Geological facts
Flint was the primary material for prehistoric technology for over two million years. It creates sparks when struck against steel due to the friction scraping off iron particles that spontaneously ignite.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture edges and waxy texture. Commonly found in chalk downs, beach shingles, and river gravels.
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