sedimentary

Weathered chert or chalcedony nodule

Microcrystalline quartz (SiO₂), possibly jasper-bearing chert

AI-generated identification · may be incorrect

Typically hardness 6.5–7, vitreous to waxy luster, opaque brown/tan coloration, and no visible cleavage; conchoidal fracture is characteristic. The specimen appears water-worn, with iron-oxide staining and a gray-brown microcrystalline interior.

Identified August 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich groundwater replaces or precipitates within marine limestone, chalk, or sedimentary layers; some varieties form from compacted siliceous ooze. Its exact age cannot be determined from the photograph and may range from Paleozoic to Cenozoic.

Uses & applications

Common chert is used historically for sharp tools and occasionally as aggregate or landscaping stone; attractive jasper/chalcedony pieces are polished for cabochons and lapidary collections.

Geological facts

Chert can produce extremely sharp edges when fractured and may spark with steel because of its high silica content. Brown, yellow, and red colors commonly result from iron oxides.

Field identification & locations

Look for hardness sufficient to scratch glass, a smooth waxy surface, and curved conchoidal breaks; it should not fizz in dilute hydrochloric acid. Common sources include limestone regions, river gravels, and glacial deposits worldwide.