sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: tan, gray, or white; Luster: dull to earthy; Crystal structure: microcrystalline (calcite); Cleavage: none in rock form; Specific Gravity: 2.5-2.7

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

Identified May 4, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: tan, gray, or white; Luster: dull to earthy; Crystal structure: microcrystalline (calcite); Cleavage: none in rock form; Specific Gravity: 2.5-2.7

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form through chemical precipitation from ocean water or lakes. Most accessible limestone is between 300-500 million years old.

Uses & applications

Extensively used in construction as an aggregate for road bases and railroad ballast, in the manufacturing of cement, as a soil conditioner in agriculture, and as a flux in steel making.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in the Grand Canyon's upper layers and is the source of many of the world's most famous cave systems.

Field identification & locations

Identify in the field by its softness (can be scratched by a penny) and its effervescence (bubbling) when a drop of dilute hydrochloric acid or strong vinegar is applied. Common worldwide in ancient sea beds.