Limestone

Physical Properties

Hardness: 3 (Mohs scale); Color: gray, light brown, tan; Luster: dull to earthy; Structure: non-crystalline visible, often massive; Cleavage: none in rock form; Density: 2.5-2.7 g/cm3.

Formation & Geological History

Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. May also form chemically through the precipitation of calcium carbonate from lake or ocean water.

Uses & Applications

Used primarily in construction for building stone, aggregate for road bases, and a key ingredient in cement (Portland cement). Also used as a soil conditioner in agriculture (lime) and as a flux in steel making.

Geological Facts

Limestone occupies about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in karst landscapes, where its solubility in rainwater leads to the creation of massive cave systems.

Field Identification & Locations

Identify in the field by its tendency to fizz (effervesce) when a drop of weak hydrochloric acid is applied. Look for fossils or distinct layering. Often found in proximity to shale and sandstone.

Identified on: 4/18/2026

Mode: Standard