sedimentary

Chert (Nodule)

Chert (Silicon Dioxide, SiO2)

Hardness: 7 (Mohs scale); Color: tan, brownish-orange from iron staining, with greyish-white interior; Luster: waxy to dull; Crystal structure: microcrystalline/cryptocrystalline; Cleavage: none, exhibits conchoidal fracture.

Hardness: 7 (Mohs scale)
Luster: waxy to dull

Identified June 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily by the precipitation of silica from groundwater in limestone or chalk beds, or as a biochemical sediment on the ocean floor from the skeletal remains of radiolaria or diatoms. Geological age can range from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modern uses include grinding media, decorative landscaping stone, and occasionally used in the production of glass or as a flint for fire-starting.

Geological facts

This specimen appears to be a weathered chert nodule or pebble. Because of its extreme hardness and chemical stability, chert often survives as pebbles in riverbeds or soil long after the surrounding limestone host rock has weathered away.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a steel nail), smooth waxy texture on broken surfaces, and rounded 'nodular' shape. Commonly found in gravel pits, riverbeds, and sedimentary basins.