sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically gray, white, or tan; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.5 - 2.8

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

Identified March 29, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically gray, white, or tan; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.5 - 2.8

Formation & geological history

Formed primarily in marine environments by the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from lake or ocean water. Significant deposits date from the Cambrian period to the present.

Uses & applications

Extensively used in construction as an aggregate for road base and railroad ballast, a raw material in cement and glass manufacturing, and as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary component of most of the world's famous cave systems through the process of karstification.

Field identification & locations

Identify in the field by its soft texture (can be scratched by a copper penny) and its strong effervescent reaction to dilute hydrochloric acid or white vinegar. Commonly found in outcroppings near riverbeds and ancient seafloors.