sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, white, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None usually visible; Specific gravity: 2.5-2.7

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

Identified June 29, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, white, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None usually visible; Specific gravity: 2.5-2.7

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in clear, warm, shallow marine waters. Can also form by precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Extensively used in construction as an aggregate, cement manufacturing, soil conditioner in agriculture, and for producing lime. Decorative varieties are used in landscaping and architecture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary host rock for many of the world's most famous cave systems, as it dissolves in acidic groundwater.

Field identification & locations

Identify by testing with a drop of dilute hydrochloric acid; it will effervesce (fizz) vigorously. Look for visible fossils or shell fragments. Commonly found in massive beds across the Midwestern US and Southern Europe.