sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Tan, beige, or gray; Luster: Dull/earthy; Crystal Structure: Trigonal (microcrystalline calcite); Cleavage: None visible in hand specimen; Specific Gravity: 2.3-2.7

Hardness: 3 on Mohs scale
Color: Tan, beige, or gray
Luster: Dull/earthy

Identified June 24, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Tan, beige, or gray; Luster: Dull/earthy; Crystal Structure: Trigonal (microcrystalline calcite); Cleavage: None visible in hand specimen; Specific Gravity: 2.3-2.7

Formation & geological history

Formed through the accumulation of shell, coral, algal, and fecal debris in marine environments. Most common in shallow, warm sea waters. This specimen appears weathered/rounded by water action.

Uses & applications

Major ingredient in cement/concrete, used in soil treatment to neutralize acidity, building stone, and for aggregate in road construction.

Geological facts

Limestone covers about 10% of the total surface area of the Earth's dry land. It is the primary rock type found in caves and karst topography and often preserves marine fossils.

Field identification & locations

Identify by its reaction (fizzing) to dilute hydrochloric acid or vinegar. Often found in riverbeds or coastal areas. Collectors should look for hidden fossils or crystal pockets within the matrix.