sedimentary
Chert (Cherty Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically tan, brown, or gray with waxy luster; Crystal Structure: Trigonal (microscopic); Cleavage: none, breaks with conchoidal fracture (shell-like curves); Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- typically tan, brown, or gray with waxy luster
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Physical properties
Hardness: 7 on Mohs scale; Color: typically tan, brown, or gray with waxy luster; Crystal Structure: Trigonal (microscopic); Cleavage: none, breaks with conchoidal fracture (shell-like curves); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or by chemical precipitation from silica-rich fluids within limestone or chalk beds. Often dated from the Paleozoic to Mesozoic eras.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction aggregate, road surfacing, and as a low-cost gemstone/tumbled stone for collectors.
Geological facts
Chert has been crucial to human evolution as it was one of the primary materials used for 'flint' tools and starting fires due to its spark-producing ability when struck against steel.
Field identification & locations
Identify in the field by its sharp, glass-like edges when broken and its ability to scratch glass. Commonly found in riverbeds, glacial tills, and as nodules within limestone outcrops.
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