Limestone

Physical Properties

Hardness: 3 on Mohs scale; Color: tan, cream, or light grey; Luster: dull to earthy; Texture: fine-grained to clastic; Cleavage: none; Specific Gravity: 2.5-2.7.

Formation & Geological History

Primarily formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the precipitation of calcium carbonate from lake or ocean water.

Uses & Applications

Used extensively in construction (aggregate, cement), agriculture (lime to neutralize soil acidity), and as a filler in products like toothpaste, paper, and plastics.

Geological Facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most of the world's caves are formed in limestone because it is easily dissolved by acidic groundwater.

Field Identification & Locations

Identify in the field by its softness (can be scratched by a copper coin) and its effervescence (bubbles) when a drop of weak acid is applied. Commonly found in areas that were once ancient sea beds.

Identified on: 5/1/2026

Mode: Standard