sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, white, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral in calcite crystals but often massive; Specific gravity: 2.3 to 2.7.

Hardness: 3 on Mohs scale
Color: Grey, white, or tan
Luster: Dull to earthy

Identified March 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from ocean or lake water. Geological ages range from Precambrian to Holocene.

Uses & applications

Extensively used in construction as an aggregate, a key ingredient in cement (Portland cement), a soil conditioner in agriculture, and for architectural cladding. High-purity limestone is used in glassmaking and chemical processes.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary component of karst landscapes, leading to the formation of massive cave systems and sinkholes due to its solubility in slightly acidic rainwater.

Field identification & locations

Identify in the field by its soft grey color, presence of fossils, and its distinctive effervescence (fizzing) when a drop of dilute hydrochloric acid or strong vinegar is applied. Commonly found in former seabed regions.