sedimentary

Limestone

Limestone (CaCO3)

Hardness: 3 (Mohs scale); Color: light gray, tan, or white; Luster: dull to earthy; Structure: fine-grained, microcrystalline or clastic; Specific gravity: 2.3 to 2.7.

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

Identified June 12, 2026More sedimentary →

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Physical properties

Hardness: 3 (Mohs scale); Color: light gray, tan, or white; Luster: dull to earthy; Structure: fine-grained, microcrystalline or clastic; Specific gravity: 2.3 to 2.7.

Formation & geological history

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form via chemical precipitation from lake or ocean water. Significant deposits range across all geological ages, especially the Paleozoic era.

Uses & applications

Extensively used in construction as an aggregate for road bases and railroad ballast, in the manufacturing of cement/lime, and as a soil conditioner in agriculture. High-grade varieties are used as dimension stone for buildings.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. It is the primary rock type found in karst landscapes, resulting in the formation of spectacular cave systems.

Field identification & locations

Identified in the field by its softness (can be scratched by a copper coin) and its strong effervescence (fizzing) when coming into contact with a drop of dilute hydrochloric acid. It is commonly found in ancient seabed regions.