sedimentary

Chert or silicified fossil nodule (tentative)

Microcrystalline quartz (SiO₂), possibly fossiliferous chert

AI-generated identification · may be incorrect

Identified August 16, 2026More sedimentary →

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Physical properties

Pale gray, cream, and tan; dull to slightly waxy luster; very fine-grained, massive texture, with indistinct conchoidal-looking fractures. Mohs hardness about 6.5–7; cleavage absent; specific gravity roughly 2.6. The rounded, irregular form and swirling surface patterns may represent silicified fossil structure, but the image alone cannot confirm this.

Formation & geological history

Chert forms when silica replaces carbonate fossils or precipitates in marine sediment, commonly during diagenesis; its age depends on the host formation and may range from Paleozoic to Cenozoic. The specimen may also be a weathered siliceous cobble.

Uses & applications

Used historically for sharp tools and fire-starting, and today as a lapidary or display material; non-ornamental chert has limited industrial value.

Geological facts

Chert can preserve exceptionally detailed fossils because silica replaces original shell or skeletal material. A steel file should barely scratch it, while a glass plate may be scratched by a fresh edge.

Field identification & locations

Common in limestone and marine sedimentary regions, including the Midwest and many coastal areas. Look for waxy luster, conchoidal fracture, hardness, and microscopic fossil textures; acid testing is usually non-diagnostic.