sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 Mohs; Color: Tan, brown, or grey; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 7 Mohs
- Color
- Tan, brown, or grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 Mohs; Color: Tan, brown, or grey; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed in marine environments through the accumulation of silica-rich microfossils or via chemical precipitation in limestone or chalk beds.
Uses & applications
Used historically for stone tools (arrowheads), as a fire-starter, in decorative landscaping, and as a component in road base or abrasive grit.
Geological facts
Chert is so hard it can scratch glass and steel. It was one of the most vital materials for early humans because its conchoidal fracture creates razor-sharp edges.
Field identification & locations
Identify by its 'glassy' smooth texture when broken and its characteristic bowl-shaped (conchoidal) fractures. Found frequently in riverbeds or within limestone outcrops.
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