sedimentary
Chert (Flint)
Microcrystalline or cryptocrystalline quartz (SiO2)
AI-generated identification · may be incorrectHardness: 7 on Mohs scale; Color: Gray, brown, black, or tan; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Gray, brown, black, or tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, brown, black, or tan; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids in limestone or chalk beds. It can date from the Precambrian to Holocene.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Modern uses include road surfacing, high-quality gemstones (when colorful), and fire-starting strikers.
Geological facts
Flint is a variety of chert that occurs in chalk or marly limestone. Because it produces sparks when struck against steel, it was the primary mechanism for ignition in flintlock firearms.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its characteristic shell-like (conchoidal) fracture pattern. Commonly found in riverbeds or as nodules within limestone outcrops.
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