sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Gray, light blue-gray, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Gray, light blue-gray, tan
Luster: Waxy to dull

Identified July 12, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Gray, light blue-gray, tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed from the accumulation of microscopic siliceous organisms (like radiolarians or diatoms) or by chemical precipitation in marine environments. This river-worn pebble likely dates from the Cretaceous period in many regions.

Uses & applications

Historically used for making stone tools (arrowheads). Modern uses include road surfacing, jewelry (tumbled stones), and as a component in abrasive materials.

Geological facts

Flint is a variety of chert that occurs primarily in chalk or marly limestone deposits. It was one of the first minerals ever exploited by humans for its ability to produce sharp edges when struck.

Field identification & locations

Identify in the field by its smooth, river-worn texture and conchoidal (shell-like) fracture patterns if broken. It will easily scratch glass. Commonly found in riverbeds and coastal regions.