sedimentary

Gray chert (flint) nodule

Microcrystalline quartz (SiO₂), likely chert

AI-generated identification · may be incorrect

Opaque, mottled gray with a waxy-to-dull luster and irregular conchoidal-looking breaks; quartz hardness is 7 Mohs, though this small rough specimen cannot be tested visually. Chert has no visible crystal structure or cleavage and typically has a specific gravity near 2.6.

Identified October 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica accumulates and replaces material in sedimentary deposits, commonly limestone or chalk; its age depends on the host formation and cannot be determined from the image.

Uses & applications

Chert has historically been used for tools and fire-starting; suitable pieces may be fashioned into decorative objects or collected.

Geological facts

Chert is composed of extremely fine quartz crystals, too small to distinguish individually without magnification.

Field identification & locations

The rounded, knobbly gray shape and fine-grained appearance are consistent with a chert nodule, but the image alone cannot confirm the identification. Chert occurs worldwide in sedimentary rocks; a fresh broken surface and hardness test can help distinguish it from softer stones.