sedimentary
Chert / Flint
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Light gray to tan with faint banding; Luster: Dull to waxy; Fracture: Conchoidal; Specific Gravity: ~2.65
- Hardness
- 7 on Mohs scale
- Color
- Light gray to tan with faint banding
- Luster
- Dull to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Light gray to tan with faint banding; Luster: Dull to waxy; Fracture: Conchoidal; Specific Gravity: ~2.65
Formation & geological history
Formed through the precipitation of silica from aqueous solutions, often in marine sedimentary environments as nodular concretions within limestone or chalk deposits.
Uses & applications
Historically used for making stone tools, arrowheads, and strike-a-light fire starters due to its conchoidal fracture producing sharp edges. Modernly used in road aggregate and landscaping.
Geological facts
Chert has been used by humans for hundreds of thousands of years for toolmaking. When struck against steel, flint produces sparks used to ignite tinder.
Field identification & locations
Identified by its microcrystalline texture, lack of visible grains, high hardness (scratches glass), and shell-like (conchoidal) curved fracture surfaces. Very common in sedimentary rock formations worldwide.
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