sedimentary
Chert (often called Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Grey, black, or brown with waxy luster; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Grey, black, or brown with waxy luster
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Grey, black, or brown with waxy luster; Crystal Structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or the chemical precipitation of silica in sedimentary basins under low-temperature conditions.
Uses & applications
Historically used for tools and weapons (arrowheads/knives) due to its sharp edges; used in industrial grinding media, road surfacing, and fire-starting kits.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone; it was one of the first materials traded over long distances by prehistoric humans.
Field identification & locations
Identify in the field by its distinctive conchoidal (shell-like) fracture and smooth, waxy surface. It is commonly found as nodules inside limestone or chalk formations. It will easily scratch glass.
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