sedimentary

Chert (Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

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

Identified June 17, 2026More sedimentary →

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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.