sedimentary

Chert (Flint)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 on Mohs scale. Color: Gray, tan, or white with a waxy to dull luster. Crystal structure: Cryptocrystalline. Cleavage: None, exhibits prominent conchoidal (shell-like) fracture. Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, tan, or white with a waxy to dull luster

Identified July 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical precipitation of silica from groundwater within sedimentary beds, typically limestone or chalk. Can be of any age, from Precambrian to recent.

Uses & applications

Historically used for stone tools, arrowheads, and fire-starting. Currently used as an abrasive, in road construction, and as a decorative landscaping stone. High-quality colorful varieties are used in lapidary work.

Geological facts

Chert was one of the most important raw materials for early humans due to its ability to be chipped into sharp edges. 'Flint' is a variety of chert typically found in chalk or marly limestone.

Field identification & locations

Identify in the field by its very smooth, glass-like fracture surfaces and extreme hardness (it will easily scratch glass). Common in limestone outcrops and as river cobbles in sedimentary basins.