sedimentary
Chert (Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
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: 2.6-2.7
- 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: 2.6-2.7
Formation & geological history
Formed as nodules or beds in limestone or chalk through the accumulation of siliceous remains (like sponges or radiolarians) or chemical precipitation from hydrothermal fluids.
Uses & applications
Historically used for stone tools (knapping) and fire-starting flint; currently used as a road aggregate, in jewelry as jasper or agate, and as a raw material for silicon production.
Geological facts
Flint is a variety of chert that has been vital to human technology for millions of years, from the earliest hand axes to the flintlock mechanisms of early firearms.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy feel, and characteristic conchoidal (shell-like) fracture patterns with sharp edges. Common in sedimentary basins worldwide.
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