sedimentary

Chert (or Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Greyish-white to tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs scale
Color: Greyish-white to tan
Luster: Waxy to dull

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Greyish-white to tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed primarily through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical precipitation of silica in marine environments or groundwater. Commonly found in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modern uses include road surfacing, jewelry (as jasper/agate varieties), and as a sparking mechanism in flintlock firearms.

Geological facts

Chert has a conchoidal fracture, creating very sharp edges similar to glass. It was one of the most important raw materials for prehistoric humans across all continents.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel) and smooth, curved fracture surfaces. It often feels slightly waxy to the touch and strikes sparks against steel.