sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, white, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Gray, tan, white, or brown
Luster: Waxy to dull

Identified April 8, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, white, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (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 groundwater within limestone or chalk beds. Found globally in geological formations ranging from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges. Modernly used as a decorative stone, in construction aggregate, and for starting fires (flint and steel).

Geological facts

Chert was one of the first materials ever 'mined' by early humans. This specific specimen appears to be a 'debitage' flake, which is the waste material created during the process of flintknapping stone tools.

Field identification & locations

Identify by its 'conchoidal' (shell-like) fracture pattern and its ability to scratch glass. It often feels smooth or waxy to the touch and has very sharp edges when broken.