sedimentary
Chert (variations include Flint or Jasper)
Chert (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: White, tan, brown, or grayish-yellow. Luster: Dull to waxy. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.5-2.8.
- Hardness
- 6
- Color
- White, tan, brown, or grayish-yellow
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: White, tan, brown, or grayish-yellow. Luster: Dull to waxy. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.5-2.8.
Formation & geological history
Formed through the accumulation of siliceous remains of organisms like diatoms or radiolarians, or through chemical precipitation of silica-rich fluids. Commonly found in limestone or chalk beds as nodules or layers.
Uses & applications
Historically used for stone tools and arrowheads. Currently used as a road aggregate, in glass manufacturing (if pure silica), and for flint-and-steel fire starting.
Geological facts
Chert nodules are often called 'flint' when found in chalk. Because it breaks with a very sharp edge (conchoidal fracture), it was the primary material for survival tools during the Stone Age.
Field identification & locations
Identify in the field by its hardness (will scratch glass), waxy feel, and smooth curved surfaces where broken. Found in riverbeds and limestone outcrops.
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