Limestone

Physical Properties

Hardness: 3-4 (Mohs); Color: Grey, white, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Irregular fracture; Specific gravity: 2.5-2.7

Formation & Geological History

Formed in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also be precipitate from lake or ocean water (chemical sedimentary rock).

Uses & Applications

Used primarily in construction as road base, railroad ballast, and an ingredient in cement. Also used as a soil conditioner and in the manufacture of glass.

Geological Facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Most cave systems are formed in limestone due to its solubility in slightly acidic water.

Field Identification & Locations

Identify in the field by applying a drop of dilute hydrochloric acid; it will effervesce (fizz). Commonly found in areas that were once ancient sea beds.

Identified on: 4/14/2026

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