sedimentary
Chert (specifically Flint or Jasper variant)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Olive green to dark brown/grey; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Olive green to dark brown/grey
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Olive green to dark brown/grey; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (has conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine or freshwater environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for making stone tools (arrowheads, knives) due to its sharp conchoidal fracture. Today used in construction aggregate, as a gemstone (Jasper), and for fire-starting (flint and steel).
Geological facts
Chert was one of the most vital materials for early humans; it can be knapped to create edges sharper than a modern surgical scalpel. It is highly resistant to weathering.
Field identification & locations
Identify in the field by its smooth, waxy feel and shell-like (conchoidal) breaking pattern. It will easily scratch glass. Commonly found in stream beds or within sedimentary outcrops.
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