sedimentary
Chert (Flint)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Gray, brown, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, brown, or tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, brown, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed primarily in marine environments where silica-rich fluids replace calcium carbonate and organic materials within sedimentary layers like limestone or chalk.
Uses & applications
Historically used for stone tools and starting fires; currently used in construction aggregate and as a collector's specimen.
Geological facts
Chert is essentially the same mineral as jasper and flint, distinguished primarily by color and transparency. It was once the most important material for early human technology.
Field identification & locations
Identified by its sharp, glass-like conchoidal fracture patterns and ability to scratch glass. Commonly found as nodules in limestone beds.
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