sedimentary

Iron-stained chert (flint) nodule

Microcrystalline quartz (SiO₂), with iron-oxide staining

AI-generated identification · may be incorrect

Hardness about 7 Mohs; tan, rusty-orange, and dark gray-black; dull weathered rind with a waxy-to-glassy dark surface. Very fine-grained, with no visible crystals or cleavage; typically breaks with curved, sharp conchoidal fractures.

Identified September 29, 2026More sedimentary →

Explore Iron-stained chert (flint) nodule in the encyclopedia →

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Physical properties

Formation & geological history

Silica-rich sediment or limestone replacement formed the chert; iron oxides colored the outer surface during weathering. The image alone cannot establish its age; chert nodules occur in sedimentary rocks of many geological periods.

Uses & applications

Chert has historically been used for tools and fire-starting; attractive pieces are collected or made into small ornaments. This specimen appears to have modest display value.

Geological facts

The contrast between a pale weathered cortex and dark, smooth interior is typical of some chert nodules.

Field identification & locations

Look for a very hard, fine-grained surface and sharp conchoidal breaks; common in limestone and chalk deposits worldwide. The image supports a chert identification, but field context or a fresh break would help confirm it.