sedimentary

Flint / Chert Nodule

Sedimentary cryptocrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale, colors typically range from grey, white, brown to black, vitreous to waxy luster, amorphous or cryptocrystalline crystal structure, conchoidal fracture with no cleavage, specific gravity around 2.60 to 2.65.

Identified July 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the replacement of calcium carbonate by silica-rich solutions in marine environments (such as chalk or limestone beds) during the Cretaceous period and other geological epochs.

Uses & applications

Historically used for making stone tools, arrowheads, and spark-producing fire starters; modern uses include landscaping gravel, abrasive materials, and lapidary collections.

Geological facts

Flint was one of the earliest materials manipulated by prehistoric humans for survival tools due to its predictable conchoidal fracture, which allows it to be shaped with extremely sharp edges through knapping.

Field identification & locations

Easily identified by its distinctive chalky outer cortex and the smooth, glassy, conchoidal fracture of the inner core. Commonly found embedded in chalk formations or as water-worn pebbles in riverbeds and beaches.

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Banded Siltstone / Mudstone Pebble

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Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)

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Shale

Shale (clastic sedimentary rock)

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