sedimentary
Chert (Flint)
Silicon Dioxide (SiO2) - Cryptocrystalline Quartz
Hardness: 7 (Mohs scale); Color: Dark grey to black (likely flint variety); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (shows conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Dark grey to black (likely flint variety)
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Dark grey to black (likely flint variety); Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (shows conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed from the accumulation of silica-rich marine organisms (like diatoms or radiolarians) or through chemical precipitation in limestone/dolomite cavities. Common in Phanerozoic sedimentary sequences.
Uses & applications
Historically used for making stone tools (arrowheads, knives) due to sharp edges; used as a fire starter when struck against steel; road aggregate and decorative landscaping.
Geological facts
Flint is the most common name for dark-colored chert. It has been vital to human technology since the Stone Age and was a primary industrial material for fire-starting before matches.
Field identification & locations
Identify by its characteristic 'curved' conchoidal fracture patterns and inability to be scratched by a steel knife. Commonly found as nodules in limestone beds or as water-worn pebbles in riverbeds.
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