sedimentary
Chert (or Flint)
Microcrystalline or cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Grey, brown, or tan with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale), Color: Grey, brown, or tan with waxy luster
- Color
- Grey, brown, or tan with waxy luster
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Physical properties
Hardness: 7 (Mohs scale), Color: Grey, brown, or tan with waxy luster. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.
Formation & geological history
Formed primarily through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids in sedimentary basins. These specimens often date from the Precambrian to present.
Uses & applications
Historically used for stone tools and weapons (arrowheads). Modernly used as a decorative stone, in road construction, and for fire-starting (flint strikers).
Geological facts
Chert is so hard it can scratch steel. When broken, it produces a conchoidal (shell-like) fracture that creates sharp edges, which is why it was the primary material for prehistoric tools.
Field identification & locations
Identify in the field by its smooth, waxy texture, hardness, and sharp, curved fracture edges. Commonly found as nodules in limestone or chalk beds.
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