sedimentary

Chert Nodule

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Tan, brown, yellowish-gray to dark gray. Luster: Earthy to waxy/dull. Cleavage: None (conchoidal fracture). Specific Gravity: ~2.65.

Hardness: 7 on Mohs scale
Color: Tan, brown, yellowish-gray to dark gray
Luster: Earthy to waxy/dull

Identified July 27, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale. Color: Tan, brown, yellowish-gray to dark gray. Luster: Earthy to waxy/dull. Cleavage: None (conchoidal fracture). Specific Gravity: ~2.65.

Formation & geological history

Formed in sedimentary rock formations (like limestone or chalk) as secondary nodules through chemical precipitation of silica-rich fluids replacing original carbonate materials.

Uses & applications

Historically used by indigenous peoples for stone tool production (arrowheads, scrapers). Today used as aggregate, decorative stone, and educational specimens.

Geological facts

Chert nodules often form around organic remains in ancient seabed environments, creating round, potato-like stones with a weathering rind on the outer surface.

Field identification & locations

Identified by its rounded nodular shape, dull tan/brown exterior weathering rind, smooth conchoidal fracture when broken, and extreme hardness (scratches glass/steel). Commonly found in limestone quarries, stream beds, and chalk deposits worldwide.