sedimentary

Iron-rich brown flint or chert nodule

Microcrystalline quartz (SiO₂), likely limonite/goethite-stained chert

AI-generated identification · may be incorrect

Very fine-grained, opaque brown to black surface with rusty iron-oxide coloration and dull to waxy luster; quartz hardness about 7, conchoidal fracture, no cleavage, and specific gravity near 2.6. The rounded, glossy form may reflect natural weathering or tumbling/polishing.

Identified September 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica replaces or precipitates within sedimentary rocks, commonly limestone or chalk; iron-bearing groundwater can produce brown goethite/limonite staining. The specimen’s precise geological age cannot be determined from the image.

Uses & applications

Used historically for sharp tools and fire-starting; attractive pieces are collected or used as lapidary material. It has little commercial construction value at this size.

Geological facts

Chert can resemble glassy volcanic rock but is typically lighter in weight than metallic ore and breaks with sharp conchoidal edges. The rusty brown color indicates oxidation of iron minerals.

Field identification & locations

Identify by testing for hardness: it should scratch ordinary glass, while a steel file generally does not scratch it. Common occurrences include limestone, chalk, gravel deposits, and riverbeds worldwide.