sedimentary
Chert (often called Flint or Jasper depending on color)
Chert (SiO2 - Microcrystalline or Cryptocrystalline Quartz)
AI-generated identification · may be incorrectHardness: 7 on Mohs scale; Color: Tan, brown, or gray; Luster: Dull to waxy; Structure: Cryptocrystalline (crystals too small to see); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.7.
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, or gray
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, or gray; Luster: Dull to waxy; Structure: Cryptocrystalline (crystals too small to see); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.7.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or via chemical precipitation from silica-rich fluids in sedimentary basins. It can be found in rock layers dating from the Precambrian to the present.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used in modern times as road surfacing material, in concrete aggregate, and as a component in glass and ceramics. High-quality colorful varieties are used for jewelry and lapidary art.
Geological facts
Chert is so hard it can easily scratch glass and steel. Because it fractures with very sharp edges (conchoidal fracture), it was the primary material used by prehistoric humans for hunting and survival tools for millions of years.
Field identification & locations
Identify in the field by its hardness (will scratch a steel knife blade), its smooth, curved 'shell-like' fracture surfaces, and its dense, non-porous appearance. Commonly found as nodules within limestone or as bedded deposits in marine sedimentary environments.
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