sedimentary

Limestone (River Pebble)

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Light gray to tan; Luster: Dull/Earthy; Structure: Fine-grained/Microcrystalline; Specific Gravity: 2.5-2.7. It reacts via effervescence (fizzing) with dilute hydrochloric acid.

Hardness: 3 on Mohs scale
Color: Light gray to tan
Luster: Dull/Earthy

Identified July 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. This specific specimen is a river pebble, shaped by fluvial erosion which smoothed its edges over long periods of transport in water.

Uses & applications

Raw limestone is used in cement manufacturing, as a soil conditioner in agriculture, and as crushed stone for road bases. In its polished form, it is used for floor tiles and architectural facades.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most caves around the world are formed in limestone when acidic groundwater dissolves the rock over thousands of years.

Field identification & locations

Identify in the field by its soft surface (can be scratched by a steel nail) and its tendency to 'fizz' when a drop of vinegar or acid is applied. Commonly found in riverbeds, coastal areas, and ancient sea beds.

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