sedimentary
Chert (White Chert or Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: White with brownish iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- White with brownish iron staining
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White with brownish iron staining; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or by chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges. Modernly used as a decorative stone, in construction aggregate, or for striking sparks to start fires.
Geological facts
Chert has been used by humans for hundreds of thousands of years to create arrowheads, scrapers, and blades. It is essentially a chemical sedimentary rock that is almost pure silica.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail), smooth waxy texture, and conchoidal (shell-like) fracture patterns. Found worldwide in sedimentary basins.
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