sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: yellowish-brown, tan, or honey-colored; Luster: waxy to vitreous; Crystal structure: Cryptocrystalline; Cleavage: none, breaks with conchoidal (shell-like) fracture; Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: yellowish-brown, tan, or honey-colored
Luster: waxy to vitreous

Identified June 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in deep-water marine environments from the accumulation of siliceous remains of microscopic organisms (diatoms or radiolarians) or through the chemical precipitation of silica-rich groundwater replacing other minerals.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) and starting fires. Today used for landscaping, as a gemstone (jaspers), and as an abrasive in industrial applications.

Geological facts

Chert is so hard it can scratch glass and steel. When struck against steel, it can create sparks, which was the primary mechanism for flintlock firearms. Some specimens contain micro-fossils that are millions of years old.

Field identification & locations

Identified by its extremely smooth, curved (conchoidal) fracture surfaces and waxy texture. Frequently found as nodules in limestone or chalk beds or as water-worn pebbles in riverbeds.