sedimentary

Limestone with Calcite Crust

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Gray matrix with white crust; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral in calcite; Specific Gravity: 2.71

Hardness: 3 on Mohs scale
Color: Gray matrix with white crust
Luster: Dull to earthy

Identified July 6, 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. The white crust is likely a secondary precipitate of calcite or calcium carbonate formed through evaporation or mineral-rich water seepage.

Uses & applications

Limestone is extensively used in construction, road base, and as a raw material for cement. Small specimens are of interest for geological study and common rock collections.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary parent material for karst landscapes, including the formation of caves and sinkholes.

Field identification & locations

Can be identified in the field by its softness (scratched by a copper penny or steel) and its reaction to weak hydrochloric acid (it will fizz). This specimen shows a common secondary mineral growth on a sedimentary base.

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