sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grayish-white to tan; Luster: Dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.71

Hardness: 3 on Mohs scale
Color: Grayish-white to tan
Luster: Dull to earthy

Identified March 21, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grayish-white to tan; Luster: Dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.71

Formation & geological history

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form through the chemical precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Extensively used as a building material, in the manufacture of cement (Portland cement), as an aggregate for the base of roads, as a white pigment or filler in products such as toothpaste or paints, and as a soil conditioner.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Many world-famous landmarks, including the Great Pyramids of Giza and the Empire State Building, are constructed using various types of limestone.

Field identification & locations

Identify in the field by its light color and the 'fizz test'—it bubbles vigorously when a drop of dilute hydrochloric acid (or vinegar) is applied. Found globally in ancient seabed deposits. For collectors, look for embedded fossils.