sedimentary

Chert Nodule (Flint)

Silicon Dioxide (SiO2)

Hardness of 7 on the Mohs scale. Often exhibits conchoidal fracture. This specimen shows a waxy, dark grey to black interior with a yellowish-tan weathered rind (cortex). It is opaque with a non-crystalline appearance to the naked eye.

Identified June 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through a biochemical or chemical process where silica-rich fluids replace carbonate material in limestone or chalk beds. Often contains microfossils and is typically found in sedimentary marine environments.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges when fractured. Modernly used as road grit, in grinding media, or collected as geological curiosities.

Geological facts

Flint was the primary material for the 'Stone Age' technology. It is highly resistant to weathering, which is why it often remains as pebbles in soil or on beaches after the surrounding limestone has eroded away.

Field identification & locations

Identify in the field by its characteristic smooth, shell-like fracture pattern and the presence of a distinct chalky or weathered outer crust. It is common in the UK, France, and various parts of the USA (like the Mid-West).