sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3-4 (Mohs scale); Color: Light gray to white; Luster: Dull or earthy; Crystal structure: Orthorhombic or Trigonal (as calcite/aragonite); Cleavage: Perfect rhombohedral in calcite crystals; Specific Gravity: 2.5-2.7

Hardness: 3-4 (Mohs scale)
Color: Light gray to white
Luster: Dull or earthy

Identified June 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Extensively used in construction as aggregate, for making cement, as a flux in steel manufacturing, and as a soil conditioner in agriculture. Pure varieties are used in pharmaceuticals and cosmetics.

Geological facts

Limestone accounts for about 10% of the total volume of all sedimentary rocks. It is the primary building material for many famous structures, including the Great Pyramids of Giza.

Field identification & locations

Identifiable in the field by its reaction to dilute hydrochloric acid (fizzing). Often found in areas that were formerly ancient seabeds; common in riverbeds as rounded cobbles like the specimen shown.