sedimentary

Chert or flint nodule

Microcrystalline quartz (SiO₂), commonly chalcedony with possible iron-oxide staining

AI-generated identification · may be incorrect

Hardness about 7 Mohs; brown, gray, and reddish coloration; waxy to dull luster; very fine-grained, non-cleavable quartz with conchoidal fracture. The rough, dense appearance and mottled iron staining are consistent with chert, though the image alone cannot confirm the variety.

Identified August 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills cavities in limestone, chalk, or other sediment, typically during diagenesis. Its age depends on the host formation and may range from Paleozoic to Cenozoic.

Uses & applications

Used historically for sharp tools and fire-starting, and today as a lapidary material, decorative stone, aggregate, and occasional jewelry material.

Geological facts

Freshly fractured chert produces extremely sharp edges and may show translucent brown or gray margins. Flint is generally the dark, compact variety of chert, while jasper is an opaque, often strongly colored variety.

Field identification & locations

Identify it by its glassy/conchoidal fracture, very high hardness, dense feel, and inability to scratch with a steel knife; it should scratch ordinary glass. Common localities include limestone and chalk regions worldwide.