sedimentary

Chert (Flint)

Chert (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically gray, brown, or tan; Luster: waxy to dull; Crystal structure: cryptocrystalline (microscopic quartz); Cleavage: none, exhibits conchoidal fracture; Specific gravity: approx 2.65.

Hardness: 7 on Mohs scale
Color: typically gray, brown, or tan
Luster: waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica from water or through the replacement of limestone. It often occurs as nodules or layers within sedimentary rocks like limestone or chalk.

Uses & applications

Historically used for stone tools and starting fires; currently used for road surfacing, as an abrasive, and occasionally in jewelry as cabochons.

Geological facts

Flint was one of the most important resources for prehistoric humans, used to create sharp arrowheads and axe heads. It sparks when struck against steel due to its hardness.

Field identification & locations

Identify in the field by its smooth, waxy feel and the sharp edges produced by conchoidal (shell-like) fracturing. Commonly found in limestone outcrops or as river pebbles.