sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically light gray, tan, or white; Luster: dull to earthy; Crystal Structure: trigonal (when visible as calcite crystals); Cleavage: rhombohedral in calcite crystals, though often massive; Specific Gravity: 2.5 - 2.7.

Hardness: 3 on Mohs scale
Color: typically light gray, tan, or white
Luster: dull to earthy

Identified April 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily through the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form through chemical precipitation from calcium-rich waters. It spans many geological ages, from the Precambrian to the Cenozoic.

Uses & applications

Extensively used in construction as building stone, road base, and a primary ingredient in cement/concrete. Also used as a soil conditioner in agriculture and as a flux in steel making.

Geological facts

Limestone often contains fossils, providing a record of ancient marine life. Over long periods, acidic rainwater can dissolve limestone to create massive cave systems and karst landscapes.

Field identification & locations

Identify in the field by its light color and fine-grained texture; it will effervesce (fizz) vigorously when touched with a drop of dilute hydrochloric acid (vinegar can also produce a weak reaction). Commonly found in sedimentary basins and mountain ranges that were once ancient seabeds.