sedimentary
Chert (Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dark brown, grey, or olive green; Luster: Waxy to vitreous; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Dark brown, grey, or olive green
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Dark brown, grey, or olive green; Luster: Waxy to vitreous; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolaria) or chemical precipitation in marine environments; commonly found in limestone or chalk beds.
Uses & applications
Historic use for stone tools and weapons; used today in road surfacing, as grinding media, and occasionally in jewelry as gemstones.
Geological facts
Flint was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges, and it produces sparks when struck against steel.
Field identification & locations
Identify by its exceptionally smooth, glass-like curved fracture surfaces (conchoidal fracture) and a rough white outer chalky layer (cortex). Common in sedimentary basins worldwide.
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