sedimentary

Chert Nodule (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 Mohs; Color: Black core with a white or tan weathered cortex; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture).

Hardness: 7 Mohs
Color: Black core with a white or tan weathered cortex
Luster: Waxy to vitreous

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs; Color: Black core with a white or tan weathered cortex; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through chemical precipitation where silica-rich fluids replace carbonate minerals in limestone or chalk beds. Often associated with Cretaceous or Paleozoic sedimentary layers.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to sharp edges. Modernly used as a road aggregate, in glass making, and by flint-knapping hobbyists.

Geological facts

This specimen is a classic example of a 'nodule' where the interior has remained protected from weathering. Flint has been used by humans for over 2 million years to start fires and create weapons.

Field identification & locations

Identify in the field by looking for smooth, rounded pebbles that, when broken, reveal a dark, glassy interior with curved 'shell-like' fracture patterns. Common in chalk cliffs and riverbeds.