Limestone

Physical Properties

Hardness: 3 on Mohs scale; Color: Gray, white, or light beige; Luster: Dull to earthy; Crystal Structure: Trigonal (microscopic); Cleavage: Perfect rhombohedral (rarely visible in hand samples); Specific Gravity: 2.5-2.7

Formation & Geological History

Formed through the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water. Found in geological formations ranging from the Precambrian to Holocene eras.

Uses & Applications

Used extensively in construction (road base, concrete aggregate), production of lime and cement, agricultural soil conditioner, and as a dimension stone for architecture.

Geological Facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary material found in caves, where acidity in groundwater creates large cavern systems through dissolution.

Field Identification & Locations

Identify in the field by its softness (can be scratched by a copper coin) and its vigorous effervescence (fizzing) when in contact with dilute hydrochloric acid. Commonly found in areas that were once ancient sea beds.

Identified on: 4/14/2026

Mode: Standard