Limestone

Physical Properties

Hardness: 3-4 (Mohs scale); Color: White to light grey; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.3-2.7

Formation & Geological History

Formed primarily in marine environments through the accumulation of shell, coral, algal, and fecal debris, or through chemical precipitation. Occurs throughout all geological ages.

Uses & Applications

Extensively used as a building material, in the manufacture of lime and cement, as an aggregate in road construction, and as a flux in steel production.

Geological Facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary material found in caves, where it is dissolved by acidic water to form stalactites and stalagmites.

Field Identification & Locations

Identify in the field by its softness (can be scratched by a copper coin) and its effervescent reaction to dilute hydrochloric acid. Commonly found in coastal areas and ancient seabed deposits.

Identified on: 5/3/2026

Mode: Standard