sedimentary

Chert (Iron-stained)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Reddish-brown to tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Reddish-brown to tan
Luster: Waxy to dull

Identified June 9, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Reddish-brown to tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. This specimen shows oxidation from iron minerals.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges when broken. Today used in construction aggregate and as decorative landscaping stone.

Geological facts

Chert is so hard it can scratch glass. It was one of the first materials used by early humans for tool-making because it breaks in predictable, sharp flakes.

Field identification & locations

Identify by its extreme hardness and smooth, shell-like (conchoidal) fracture surfaces. Commonly found as nodules in limestone or as bedded layers in sedimentary basins.