sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Gray, black, or brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
- Hardness
- 6
- Color
- Gray, black, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Gray, black, or brown; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture)
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments, often replacing limestone.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate and as a gemstone when colorful (Jasper/Agate).
Geological facts
It breaks with a sharp edge called a conchoidal fracture, which made it the primary material for prehistoric arrowheads and spear points.
Field identification & locations
Identify by its ability to scratch glass and its waxy texture. Commonly found as nodules or layers within limestone and chalk beds.
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