sedimentary
Chert (variations include Flint/Jasper)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale); Color: Gray, tan, brown, or dull green with waxy luster; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Gray, tan, brown, or dull green with waxy luster
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Physical properties
Hardness: 7 (Mohs scale); Color: Gray, tan, brown, or dull green with waxy luster; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the accumulation of siliceous remains of organisms (like diatoms or radiolaria) or through chemical precipitation in marine or groundwater environments. Found in sedimentary beds ranging from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (arrowheads); currently used as a raw material for ceramics, construction aggregate, and occasionally as semi-precious gemstones (Jasper/Agate).
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture creates extremely sharp edges perfect for knives, scrapers, and projectiles.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy/dull luster, and distinctive curved (conchoidal) surface when broken. Found commonly in limestone outcrops or as river pebbles.
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