sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Chalky white to light beige; Luster: Dull or earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (rhombohedral in calcite crystals); Specific Gravity: 2.5-2.7

Hardness: 3 on Mohs scale
Color: Chalky white to light beige
Luster: Dull or earthy

Identified June 8, 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 as a building material, in the manufacture of cement (Portland cement), as an aggregate for the base of roads, as a white pigment or filler in products such as toothpaste or paints, and as a soil conditioner.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type in which most karst landscapes and caves form due to its solubility in slightly acidic water.

Field identification & locations

Can be identified in the field by its softness (can be scratched by a penny) and its vigorous reaction (fizzing) when a drop of diluted hydrochloric acid or strong vinegar is applied. Look for small fossil fragments or a modular, layered structure.