sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: White, gray, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: White, gray, or tan
Luster: Waxy to dull

Identified June 20, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: White, gray, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; 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. Often Cretaceous in age.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in road construction, as architectural stone, and sometimes as a low-cost gemstone for cabochons.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. When struck against steel, it can produce sparks, which made it essential for early firearms (flintlocks) and fire-making.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture pattern and its ability to scratch glass. Commonly found in riverbeds, beaches, and limestone outcrops globally.