sedimentary
Chert (Flint)
Chert (SiO2)
Hardness: 7 Mohs; Color: Gray to light tan; Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs
- Color
- Gray to light tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 Mohs; Color: Gray to light tan; Luster: Waxy to dull; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the precipitation of silica from groundwater or the accumulation of siliceous skeletal remains of marine organisms (diatoms/radiolarians) within sedimentary layers.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) and to start fires. Modern uses include road surfacing and as a minor abrasive.
Geological facts
Flint is a variety of chert. When struck against steel, it creates sparks due to the friction oxidizing the metal, a property used for centuries in flintlock firearms.
Field identification & locations
Identified by its sharp, glass-like curved (conchoidal) fractures and its ability to scratch glass. Found globally in limestone and chalk deposits.
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