sedimentary
Chert (variations include Flint or Jasper)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: Typically grey, brown, or tan with a waxy luster; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None; Fracture: Conchoidal (shell-like curves); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Typically grey, brown, or tan with a waxy luster
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Physical properties
Hardness: 7 (Mohs scale); Color: Typically grey, brown, or tan with a waxy luster; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None; Fracture: Conchoidal (shell-like curves); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical precipitation of silica in marine environments. It is often found as nodules or layers within limestone and chalk beds, occurring throughout various geological ages from the Precambrian to today.
Uses & applications
Historically used for making stone tools (arrowheads, knives) due to its sharp edges. Modern uses include road surfacing material, jewelry (when colored like Jasper), and sparking mechanisms for fire-starting.
Geological facts
Known as the 'stone of ancient technology,' chert was the primary material for the Stone Age tool industry. The conchoidal fracture pattern allows it to be shaped with extreme precision into razor-sharp blades.
Field identification & locations
Identify in the field by its very smooth, waxy surface and distinct curved (scalloped) fracture lines where it has broken. It is often found with a rough white or tan 'rind' (cortex). It is ubiquitously found in limestone-rich areas globally, such as the UK, USA (Midwest), and the Middle East.
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