sedimentary

Flint in Chalk

Sedimentary nodular chert within chalk (SiO2)

Hardness of 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline quartz (chalcedony) structure, conchoidal fracture with no cleavage, specific gravity around 2.60. Color ranges from dark grey, black, brown to whitish where weathered by a porous chalk cortex.

Identified July 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Cretaceous period (approximately 65 to 145 million years ago) through the diagenesis of silica-rich marine organism remains (such as sponges and diatoms) precipitating within accumulating calcium carbonate chalk oozes.

Uses & applications

Historically used for prehistoric stone tools, arrowheads, and fire-starting strikers. Today used as decorative landscaping aggregate, historical masonry building stone, and educational specimens.

Geological facts

Flint nodules are famously found embedded in chalk cliffs like the White Cliffs of Dover. Prehistoric humans highly prized flint for its predictable conchoidal fracture, allowing precise knapping into sharp edges.

Field identification & locations

Easily identified in the field by its distinctive outer chalky white cortex and dark, glassy interior exposed on broken surfaces. Commonly found along coastlines and rivers where chalk formations erode.

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