sedimentary

Limestone

Limestone (Calcium Carbonate, CaCO3)

Hardness: 3 (Mohs scale); Color: Gray, tan, or buff; Luster: Dull to earthy; Structure: Microcrystalline, often containing fossils; Cleavage: None; Specific Gravity: 2.3 - 2.7. Reacts with dilute hydrochloric acid.

Hardness: 3 (Mohs scale)
Color: Gray, tan, or buff
Luster: Dull to earthy

Identified July 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. In this region of Kentucky (near Louisville), these are typically Mississippian or Devonian in age (approx. 330-400 million years old).

Uses & applications

Widely used for construction aggregate, road base, cement manufacturing, soil conditioner in agriculture, and as a building stone (Kentucky Bluestone).

Geological facts

The area near 38.2°N, 85.7°W is famous for the Falls of the Ohio, which exposes one of the world's largest Devonian fossil beds. Limestone is the state rock of Kentucky and provides the calcium rich water essential for the region's bourbon distillation and thoroughbred horse industry.

Field identification & locations

Check for fossil inclusions (brachiopods or crinoids) and test with vinegar to see if it bubbles (indicates calcite). Very common in the Ohio River Valley.