sedimentary

Limestone (Weathered)

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale; Color: typically grey, tan, or white, often covered with dark organic lichen or dirt as seen here; Luster: dull to earthy; Crystal structure: orthorhombic or hexagonal; Cleavage: perfect rhombohedral in calcite crystals, but usually massive in rock form.

Hardness: 3 on Mohs scale
Luster: dull to earthy

Identified March 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the precipitation of calcium carbonate from lake or ocean water. Most limestone formed during the Paleozoic and Mesozoic eras.

Uses & applications

Extensively used in construction as aggregate, cement production, soil conditioner in agriculture, and as a decorative building stone. It is also a primary source of lime used in steel manufacturing and water treatment.

Geological facts

Limestone accounts for about 10% of the total volume of all sedimentary rocks. It is soluble in weak acids, which leads to the formation of karst topography, caves, and sinkholes over geological time.

Field identification & locations

Identify in the field by its softness (can be scratched by a steel knife) and its reaction to dilute hydrochloric acid, which causes it to effervesce (fizz). This specimen shows significant surface weathering and biological growth (crustose lichen), common for rocks found in humid outdoor environments.