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/Irregular; Specific gravity: 2.3–2.7

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

Identified June 4, 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/Irregular; Specific gravity: 2.3–2.7

Formation & geological history

Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from calcium-rich water.

Uses & applications

Used primarily in construction as a building material, road base, and ingredient in portland cement. Also used in agriculture to neutralize soil acidity and in the smelting of iron ore.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most of the world's great cave systems are formed in limestone through the action of acidic groundwater.

Field identification & locations

Identify in the field by its light color and susceptibility to weathering. It will fizz vigorously when exposed to dilute hydrochloric acid (acid test). Commonly found in ancient sea beds and mountain ranges.