sedimentary

Chert or flint nodule

Microcrystalline quartz (SiO₂), commonly chalcedony with possible opaline silica

AI-generated identification · may be incorrect

Typically hardness 6.5–7, waxy to dull luster, opaque to translucent, and conchoidal fracture; this specimen is pale gray-white with rusty iron-oxide staining. It lacks visible crystal faces and has a dense, fine-grained texture.

Identified August 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills pore spaces in limestone, chalk, or marine sediments, often during diagenesis. Individual nodules may be tens to hundreds of millions of years old, depending on their host formation.

Uses & applications

Historically used for sharp tools, arrowheads, and fire-starting; today it is mainly a teaching or collector specimen, with limited ornamental use.

Geological facts

Chert and flint are mineralogically similar; “flint” usually refers to dark, high-quality chert associated with chalk. Its conchoidal fracture can produce extremely sharp edges.

Field identification & locations

Look for a smooth waxy surface, very fine grain, no cleavage, and curved fracture surfaces; it should scratch glass but not be scratched by a steel knife. Common in limestone and chalk regions worldwide.