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 in massive form; Specific Gravity: 2.3-2.7

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

Identified July 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 in massive form; Specific Gravity: 2.3-2.7

Formation & geological history

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

Uses & applications

Used primarily in construction (crushed stone), cement manufacturing, soil conditioner in agriculture, and as a precursor for lime.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Most cave systems find their home in limestone formations due to its solubility in slightly acidic water.

Field identification & locations

Can be identified in the field by its softness (scratchable by a steel blade) and its effervescent reaction when exposed to dilute hydrochloric acid or strong vinegar.