sedimentary

Chert (Nodule)

Chert (Silica, SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Tan, brownish-gray, and cream. Luster: Dull to waxy. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Tan, brownish-gray, and cream
Luster: Dull to waxy

Identified June 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale. Color: Tan, brownish-gray, and cream. Luster: Dull to waxy. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or by chemical precipitation from silica-rich fluids within limestone or chalk beds during the Phanerozoic eon.

Uses & applications

Historically used for stone tools (arrowheads). Modern uses include road surfacing, decorative landscaping, and occasionally as a source of high-purity silica for industrial glass.

Geological facts

Chert is so hard it can strike sparks against steel. Because of its conchoidal fracture, it was one of the most important materials for early human technology, used to make sharp-edged scrapers and knives.

Field identification & locations

Identify in the field by its hardness (will scratch glass), smooth waxy feel on broken surfaces, and lack of reaction to acid. Often found as rounded nodules or layers within sedimentary rock outcrops.