sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs, Color: White, tan, with brown inclusions. Luster: Waxy to dull. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture).

Hardness: 7 Mohs, Color: White, tan, with brown inclusions
Color: White, tan, with brown inclusions
Luster: Waxy to dull

Identified June 28, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs, Color: White, tan, with brown inclusions. Luster: Waxy to dull. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture).

Formation & geological history

Forms primarily as nodules or layers in limestone or chalk through the accumulation of silica-rich marine organisms like sponges or radiolarians. The silica precipitates and replaces original carbonate material.

Uses & applications

Historically used for stone tools and weapons (arrowheads). Modernly used in construction aggregate, as flint for fire-starting, and occasionally as minor gemstone lapidary material.

Geological facts

Flint is a variety of chert that was essential to prehistoric humans because it fractures with extremely sharp edges. It is often found with a white 'cortex' or weathered outer layer.

Field identification & locations

Identified by its sharp conchoidal (shell-like) fracture edges and its ability to scratch glass. Found often on beaches, in riverbeds, or embedded in limestone cliffs.