sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: Grayish-brown with mottled waxy patterns, Luster: Waxy to vitreous, Crystal structure: Microcrystalline/Cryptocrystalline (trigonal), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6

Identified July 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids in sedimentary basins or limestone cavities. Can date from the Precambrian to recent eras.

Uses & applications

Historically used for stone tools and starting fires (striking steel). Modern uses include abrasives, road surfacing, and as a semi-precious tumbled stone for collectors.

Geological facts

Chert and flint are essentially the same material; 'flint' is often specifically used for chert found in chalk or limestone beds. It was one of the most important minerals for early humans due to its ability to form sharp, durable edges when fractured.

Field identification & locations

Identify in the field by its smooth, waxy feel and prominent curved 'shell-like' (conchoidal) fractures. It will easily scratch glass. Found worldwide, often in limestone or chalk deposits and as water-worn pebbles in stream beds.