sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Gray to light tan/off-white; Luster: Dull to earthy; Texture: Fine-grained, microcrystalline to bioclast-rich; Reaction: Effervesces vigorously with dilute hydrochloric acid.

Hardness: 3 on Mohs scale
Color: Gray to light tan/off-white
Luster: Dull to earthy

Identified July 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in warm, shallow marine environments through the accumulation and compaction of organic debris like shells, coral, and algal remains, or via direct chemical precipitation of calcium carbonate from water.

Uses & applications

Widely used as a major component in construction (crushed stone, cement production, architectural building stone), soil acidity neutralizer in agriculture, and chemical feedstock.

Geological facts

Limestone formations often feature extensive cave systems created by acid dissolution. Karst topography is created when rain slightly acidic from dissolved carbon dioxide slowly dissolves limestone bedrock over millennia.

Field identification & locations

Look for a light gray to tan fine-grained rock embedded in soil or exposed as bedrock. You can test it in the field using a drop of weak acid (like vinegar) to check for effervescence, and a steel knife easily scratches it.