sedimentary
Chert (and/or Flint)
Silicon dioxide (SiO2)
AI-generated identification · may be incorrectHardness: 6.5-7 (Mohs scale). Color: Gray, white, or brown with a waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None, exhibits sharp conchoidal (shell-like) fracture.
- Hardness
- 6
- Color
- Gray, white, or brown with a waxy luster
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Physical properties
Hardness: 6.5-7 (Mohs scale). Color: Gray, white, or brown with a waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None, exhibits sharp conchoidal (shell-like) fracture.
Formation & geological history
Formed as nodules or layered deposits in limestone or chalk through the accumulation of silica-rich microfossils like diatoms or radiolarians. Most common in ancient marine sedimentary sequences.
Uses & applications
Historically used for stone tools (arrowheads, knives) due to sharp edges and in fire-starting. Currently used as road metal, in decorative landscaping, or as concrete aggregate.
Geological facts
Because of its extreme hardness and tendency to fracture with razor-sharp edges, chert was the primary material for technologies in the Stone Age. It can strike sparks against steel to ignite tinder.
Field identification & locations
Identify in the field by its waxy appearance and distinct conchoidal fracture which leaves curved pits. It is very hard and cannot be scratched by a steel knife.
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