sedimentary

Likely chert (flint)

Microcrystalline quartz (SiO₂), likely chert; exact identification is uncertain from the image alone

AI-generated identification · may be incorrect

Dark gray-brown with a dull to waxy surface and pale weathered rind; quartz crystal structure is too fine to see. Hardness about 7 Mohs; typically breaks with curved, sharp-edged conchoidal fractures and has no cleavage.

Identified October 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica accumulates and replaces material in sedimentary rocks, often as nodules in limestone or chalk. Chert occurs in rocks of many geological ages; the specimen’s age cannot be determined from the image.

Uses & applications

Used historically for sharp tools and fire-starting; today it is mainly collected or used decoratively. Not identifiable as a jewelry-grade material from the photo.

Geological facts

Chert’s conchoidal fracture can produce very sharp edges, which made it valuable to prehistoric toolmakers.

Field identification & locations

Look for a hard, fine-grained interior, curved fracture surfaces, and a contrasting pale rind; these features distinguish it from many dark, coarse-grained rocks. Chert is widespread in sedimentary formations worldwide.