sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 Mohs; Color: Grey, tan, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Grey, tan, brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Grey, tan, brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the accumulation of siliceous remains of organisms like diatoms or radiolarians, or through chemical precipitation in marine or groundwater environments.
Uses & applications
Used historically for stone tools and weapons (knapping); modern uses include road surfacing, jewelry (jasper varieties), and fire-starting (flint).
Geological facts
Chert was one of the first materials used by prehistoric humans to create sharp edges. It is so tough that it can scratch steel and spark when struck against iron.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture and smooth, waxy surface. Look for it in limestone or chalk beds as nodules or massive layers.
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Brecciated Chert (Microcrystalline Silica)
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