sedimentary

Brown chert or flint nodule

Microcrystalline quartz, SiO₂ (chalcedony/quartz)

AI-generated identification · may be incorrect

Typically hardness 6.5–7, waxy to dull luster, brown or honey coloration, and very fine-grained cryptocrystalline structure; conchoidal fracture and no visible cleavage are diagnostic. The surface appears weathered or possibly polished, with iron-oxide staining.

Identified September 17, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills cavities in limestone, chalk, or other sediment; many nodules are Paleozoic–Cenozoic, though exact age cannot be determined visually. Common sources include sedimentary basins, chalk deposits, and gravel beds.

Uses & applications

Used historically for sharp tools and fire-starting, and today for ornamental objects, lapidary work, and minor aggregate. Attractive patterned pieces may interest collectors.

Geological facts

Chert is chemically similar to flint; “flint” generally denotes dark, high-quality chert capable of producing a sharp edge and sparks with steel.

Field identification & locations

Look for conchoidal breaks, a smooth waxy texture, uniform microcrystalline appearance, and inability to scratch it with a steel knife; a quartz crystal or glass can scratch it. Common in limestone regions and stream gravels.