Limestone

Physical Properties

Hardness: 3 (Mohs scale); Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Massive; Specific gravity: 2.3–2.7

Formation & Geological History

Formed from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. Can also form through the chemical precipitation of calcium carbonate from lake or ocean water.

Uses & Applications

Used primarily in construction as road base, railroad ballast, and an ingredient in cement. Used in agriculture for neutralising soil acidity and as a raw material for the chemical industry.

Geological Facts

Limestone accounts for about 10% of the total volume of all sedimentary rocks. Most caves are formed by the dissolution of limestone by slightly acidic groundwater.

Field Identification & Locations

Identify in the field by applying a drop of dilute hydrochloric acid; it will effervesce (fizz) vigorously. It is commonly found in areas that were once prehistoric seafloors.

Identified on: 4/14/2026

Mode: Standard