sedimentary

Limestone

Calcium Carbonate (CaCO3)

Mohs hardness: 3, Color: Tan to light brown/grey, Luster: Dull/Earthy, Grain size: Variable, Reacts with HCl acid.

Luster: Dull/Earthy, Grain size: Variable, Reacts with HCl acid

Identified July 15, 2026More sedimentary →

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Physical properties

Mohs hardness: 3, Color: Tan to light brown/grey, Luster: Dull/Earthy, Grain size: Variable, Reacts with HCl acid.

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. This specimen appears to be of the clastic or biogenic variety typical of coastal or lakebed deposits.

Uses & applications

Used extensively in construction (aggregate, cement), agriculture (soil conditioner), and as a base material for roads.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It often contains fossils of prehistoric marine life which are hidden within its layers.

Field identification & locations

Can be identified in the field by its softness (scratched by a copper penny) and its effervescent reaction when exposed to a weak acid like vinegar or hydrochloric acid.