The correct answer is Calcium carbonate.
Important Points
- Calcium carbonate and its forms:
- In nature, calcium carbonate occurs in the forms of chalk, limestone, and marble.
- Formation:
- The skeletal remains of dead sea animals sink to the seabed. Over millions of years, layer build-up and pressure from the top layer changes the bottom layer into chalk.
- Earth movements due to earthquake lift the layer of chalk to the Earth's surface.
- The earth's movements can also cause the layers to sink further. Thus, high pressure and heat cause the chalk to turn into much harder limestone.
- The limestone deposit may stay below the Earth for a longer time and due to higher pressure and temperature, the limestone turns to marble.



