sedimentary

Chert

SiO2 (Microcrystalline Quartz)

Hardness: 7 (Mohs scale), Color: tan, brown, or grey, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, brown, or grey, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65

Formation & geological history

Formed from the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. It typically occurs as nodules or layers within limestone and chalk beds.

Uses & applications

Historically used for stone tools (flintknapping); used today as construction aggregate, road surfacing, and as a semi-precious stone in jewelry and lapidary art.

Geological facts

Flint is a variety of chert. Because of its conchoidal fracture, it can be chipped to a razor-sharp edge, and when struck against steel, it produces sparks, making it vital for early humans for hunting and fire-making.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy appearance, and sharp, shell-like (conchoidal) edges when broken. It is extremely common in areas with limestone bedrock.