sedimentary
Chert (Flint Nodules)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, or white with a chalky outer rind; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 6
- Color
- Tan, beige, or white with a chalky outer rind
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Tan, beige, or white with a chalky outer rind; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the replacement of limestone. This specimen shows a characteristic weathering rind (cortex) common in nodules formed in carbonate environments.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used for road surfacing, as an abrasive, and in some jewelry as tumbled stones.
Geological facts
Chert is so durable that it often remains after the surrounding limestone or chalk has weathered away. It was one of the first materials traded over long distances by prehistoric humans.
Field identification & locations
Identify by its 'shell-like' conchoidal fracture which produces very sharp edges, its ability to scratch glass, and the presence of a distinct white calcium carbonate outer layer or 'rind'. Found worldwide in sedimentary basins.
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