sedimentary

Chert

Chert (SiO₂)

Hardness: 7 (Mohs scale); Color: Tan, brown, or gray with white inclusions; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Hardness: 7 (Mohs scale)
Color: Tan, brown, or gray with white inclusions
Luster: Waxy to dull

Identified July 17, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, brown, or gray with white inclusions; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6

Formation & geological history

Formed in marine environments through the accumulation of silica-rich organic remains or chemical precipitation. This specimen appears water-worn, likely from a stream or river bed.

Uses & applications

Historically used for stone tools and starting fires; currently used in construction aggregate, road surfacing, and as decorative garden stones.

Geological facts

Chert is so hard it can scratch glass and steel. It was a primary material for prehistoric arrowheads and spear points due to its sharp edges when fractured.

Field identification & locations

Identify in the field by its waxy luster, smoothness, and conchoidal (shell-like) fracture patterns. Commonly found in limestone formations or as river pebbles.