sedimentary

Chert (Nodule)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, tan, and gray with iron staining; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Brown, tan, and gray with iron staining
Luster: Dull to waxy

Identified June 27, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brown, tan, and gray with iron staining; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the chemical precipitation of silica-rich fluids within limestone or chalk beds, often replacing organic material or filling voids during diagenesis.

Uses & applications

Historically used for stone tools (flintknapping); currently used in road construction, as decorative landscaping stone, and occasionally for folk art or lapidary tumbling.

Geological facts

Chert is so durable that it often survives millions of years of erosion after its parent limestone host rock has completely weathered away. It was one of the most important minerals for early humans to create sharp edges.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by steel), waxy texture when broken, and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds or fields where limestone is the bedrock.