sedimentary

Chert Nodules

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Tan, brown, and grey; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); High durability.

Hardness: 7 Mohs scale
Color: Tan, brown, and grey
Luster: Dull to waxy

Identified May 23, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Tan, brown, and grey; Luster: Dull to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); High durability.

Formation & geological history

Formed in marine sedimentary environments through the precipitation of silica from seawater or the replacement of carbonate minerals in limestone/chalk beds during diagenesis.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers); currently used as road aggregate, decorative landscaping stone, and occasionally for lapidary work.

Geological facts

This specimen shows characteristic 'nodular' or 'concretionary' weathering where layers of silica have accumulated. These often survive erosion better than the limestone they were originally embedded in.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in limestone outcrops or riverbeds.