Limestone

Physical Properties

Hardness: 3 on Mohs scale; Color: Grey, white, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.5–2.7

Formation & Geological History

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form through chemical precipitation from ocean or lake water.

Uses & Applications

Extensively used in construction (concrete, road base), agriculture (soil conditioner), and as a chemical raw material for cement production and iron ore smelting.

Geological Facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type in karst landscapes, leading to the formation of spectacular caves and sinkholes.

Field Identification & Locations

Identified in the field by its softness (can be scratched by a copper coin/knife) and vigorous effervescence (fizzing) when a drop of dilute hydrochloric acid is applied.

Identified on: 4/27/2026

Mode: Standard