Limestone

Physical Properties

Hardness: 3 on Mohs scale; Color: typically off-white, buff, or gray; Luster: dull to earthy; Crystal structure: microcrystalline or massive calcite; Cleavage: rhombohedral in calcite crystals but often invisible in bulk rock; Specific gravity: approx 2.5-2.7.

Formation & Geological History

Formed in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from calcium-rich water. Most surface limestone is Paleozoic or Mesozoic in age.

Uses & Applications

Major ingredient in cement/concrete, used as building stone, road base, and in agricultural lime for pH balancing. High-purity limestone is used in glass making and chemical processes.

Geological Facts

Limestone contains roughly 10% of the total volume of all sedimentary rocks. It often contains fossils of marine organisms because it forms in shallow sea beds.

Field Identification & Locations

Identify in the field by testing with cold dilute hydrochloric acid; it will effervesce (fizz) vigorously. It is commonly found in areas with karst topography, caves, and cliffs. Look for light-colored, relatively soft rock that reacts to acid.

Identified on: 4/16/2026

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