sedimentary

Fossiliferous Limestone (Chert/Clay mixed)

Calcium Carbonate (CaCO3) / Silicon Dioxide (SiO2)

Hardness: 3-4 (matrix) to 7 (chert inclusions); Color: Tan, earth-brown, gray-white; Luster: Dull/Earthy to slightly waxy; Structure: Amorphous/fine-grained matrix with irregular voids and inclusions.

Hardness: 3-4 (matrix) to 7 (chert inclusions)
Color: Tan, earth-brown, gray-white
Luster: Dull/Earthy to slightly waxy

Identified June 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in a shallow marine environment during the Ordovician period (~450 million years ago) specifically common to the Cincinnati Arch region. Created through the accumulation of shell fragments and lime mud on ancient sea floors.

Uses & applications

Commonly used as crushed stone for aggregate in road construction, concrete production, and as a natural source of lime for agriculture.

Geological facts

The location provided (northern Kentucky/southern Ohio area) is world-famous for its Ordovician fossils, often found embedded in rocks exactly like this one. This specimen appears to be a weathered piece of Ordovician limestone or a chert nodule commonly found in the Lexington Limestone formation.

Field identification & locations

Identify by applying a small amount of vinegar; if the matrix fizzes, it is limestone. Look for small holes or textures which are often molds of ancient bryozoans or brachiopods common in this region.

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