sedimentary

Flint or chert nodule

Microcrystalline quartz (SiO₂), commonly chalcedony with possible opal and impurities

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray, white, and brown coloration with a waxy to dull luster. It has cryptocrystalline structure, no cleavage, conchoidal fracture, and typically specific gravity around 2.6.

Identified August 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills pores in limestone, chalk, or marine sediments, often producing nodules. Most specimens formed during the Paleozoic–Cenozoic, depending on source strata.

Uses & applications

Used historically for sharp tools and fire-starting, and today as lapidary material, decorative stone, and a collector specimen; generally not gem-grade.

Geological facts

The scalloped, glasslike fracture and very fine texture are characteristic of chert or flint. The white outer coating may be weathered silica, and the gray interior could include chalcedony or minor impurities.

Field identification & locations

Identify by testing whether it scratches glass and by its conchoidal fracture; unlike calcite, it does not effervesce in dilute acid. Common in limestone, chalk, river gravels, and glacial deposits worldwide.