sedimentary

Limestone with Calcite Vug

Calcium Carbonate (CaCO3) in Sedimentary Matrix

Hardness: 3 on Mohs scale; Color: Gray to tan matrix with white/yellowish crystals; Luster: Dull to vitreous; Crystal Structure: Trigonal/rhombohedral calcite crystals; Cleavage: Perfect rhombohedral in crystals.

Hardness: 3 on Mohs scale
Color: Gray to tan matrix with white/yellowish crystals
Luster: Dull to vitreous

Identified July 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments from the accumulation of shell, coral, and algal debris. The crystals formed later when mineral-rich groundwater filled cavities (vugs) in the rock. Typically Paleozoic to Mesozoic era.

Uses & applications

Limestone is used extensively in construction, cement production, and agriculture. Specimens with crystal vugs are collected as decorative mineral samples.

Geological facts

Limestone covers about 10% of the Earth's land surface. The crystals inside are often secondary deposits that can take thousands of years to grow within these small pockets.

Field identification & locations

Identify by its reaction (fizzing) with diluted hydrochloric acid. Look for rhombohedral crystal shapes in cavities. Commonly found in quarries, road cuts, and karst landscapes.

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