sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs; Color: Brownish-tan to grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 Mohs
Color: Brownish-tan to grey
Luster: Waxy to dull

Identified July 7, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Brownish-tan to grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed via the accumulation of siliceous remains from microscopic organisms (like diatoms or radiolaria) or chemical precipitation in sedimentary environments such as limestone or chalk beds. Commonly Phanerozoic in age.

Uses & applications

Historically used for stone tools (knapping) and starting fires; currently used in jewelry (as flint or jasper variant), road surfacing, and as a decorative stone.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. Because of its predictable conchoidal fracture, it was the primary material for prehistoric arrowheads and spear tips.

Field identification & locations

Identified by its sharp edges when broken, waxy texture, and ability to scratch glass. Often found as nodules within limestone outcrops or as rounded pebbles in stream beds.