sedimentary

Limestone

Limestone (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, tan, off-white; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None in massive form; Specific Gravity: 2.3-2.7

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

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, tan, off-white; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None in massive form; Specific Gravity: 2.3-2.7

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. Most widespread specimens date from the Paleozoic and Mesozoic eras.

Uses & applications

Extensively used in construction as building stone, road base, and a primary ingredient in Portland cement. Also used as a soil conditioner and in glass making.

Geological facts

Limestone is the primary source of the world's caves through the process of chemical weathering by slightly acidic rainwater. It often contains well-preserved fossils of ancient sea life.

Field identification & locations

Can be identified in the field by its effervescence (fizzing) when exposed to a drop of dilute hydrochloric acid. Common in areas that were once prehistoric seafloors. Look for visible shell fragments or fossils.