sedimentary

Flint in Limestone (Chert Nodule)

Sedimentary rock containing microcrystalline quartz (SiO2) within a carbonate matrix

Hardness: 7 on the Mohs scale for the flint/quartz portion and 3 for the limestone. Color: Dark grey to black nodule surrounded by white to cream-colored weathered limestone. Luster: Vitreous to dull. Fracture: Conchoidal fracture in the flint.

Luster: Vitreous to dull

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical precipitation of silica from silica-rich fluids or biological remains of siliceous organisms (like radiolarians or sponge spicules) accumulating in calcareous marine sediments, typically during the Cretaceous period.

Uses & applications

Historically used for making stone tools, arrowheads, and spark-producing fire starters. Primarily collected as a geological curiosity today.

Geological facts

Flint and chert nodules frequently weather out of limestone cliffs and riverbeds because the silica is much more resistant to weathering and erosion than the surrounding carbonate rock, resulting in striking bi-colored contrast pebbles.

Field identification & locations

Easily identified in the field by contrasting hardness and texture between the smooth, dark, glassy silica nodule and the chalky or fine-grained lighter limestone host rock.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

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Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

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Quartz pebble

Silicon dioxide (SiO2)

sedimentary

Generic Pebble / Rock Fragment

Lithic fragment / Weathered rock

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Sedimentary Sandstone

Arenite (Sedimentary Rock)

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Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

sedimentary