Limestone Formation

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Author: Jane Healey

Limestone is composed of tiny shells that fell to the ocean’s floor when sea creatures died. The pressure from other shells, the water and sand washing over them squashes the tiny shells together into rock. When the pressure continues, it can turn into marble.

Limestone is hard and durable, making it a commonly used material in architecture.The Great Pyramid of Giza is made entirely of limestone, and many buildings and statues are as well. Spectacular erosional landforms known as karsts surface in rocky outcrops and islands.

The goal of this experiment is to explore the formation of limestone as it happens in nature. Calcium carbonate is the main component that forms shells, and when marine life dies those shells settle on the bottom of the ocean where they collect. Over time, limestone is formed.


How is limestone formed?


  • Pieces of shell
  • Shoebox
  • Plastic garbage bags
  • Paper cups
  • Dry plaster
  • Water


  1. Line the shoebox with a plastic bag and cut it to fit snugly.
  2. Pour plaster and water into the bag/box and mix thoroughly.
  3. Add the shell pieces to the plaster mixture.
  4. Pour the mixture into paper cups.
  5. Place the cups in a warm place and leave them undisturbed.
  6. After 5 days, remove the limestone mixture from the cups.
  7. Compare the homemade limestone to natural samples.

[NOTE: For a more complex project, vary the locations of the paper cups and note the difference between samples.]

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