sedimentary
Chert (Flint)
Sedimentary Cryptocrystalline Quartz (SiO2)
Hardness: 7 Mohs; Color: Brown, grey, black; Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); SG: 2.65
- Hardness
- 7 Mohs
- Color
- Brown, grey, black
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Brown, grey, black; Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); SG: 2.65
Formation & geological history
Formed from the accumulation of siliceous organisms or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic
Uses & applications
Historically used for stone tools and starting fires; currently used as road aggregate and in some jewelry/ornamental pieces
Geological facts
Because it breaks with a sharp edge, it was the primary material for arrowheads and knives for prehistoric humans globally
Field identification & locations
Identified by its very hard surface (scratches glass) and smooth, shell-like (conchoidal) fracture planes; commonly found in limestone or chalk beds
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