sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

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

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

Identified May 24, 2026More sedimentary →

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Physical properties

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

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments such as limestone or chalk beds. Often Cretaceous or Jurassic in age.

Uses & applications

Historically used for stone tools and weapons due to its ability to hold a sharp edge. Modernly used in construction aggregate and as a fire-starter (flint).

Geological facts

Flint was one of the most important resources for prehistoric humans to create arrowheads and knives. It produces sparks when struck against steel, which revolutionized fire-making.

Field identification & locations

Identify by its glassy, waxy texture and sharp, shell-like (conchoidal) breaks. Often found as nodules within limestone or along riverbeds and beaches.