Limestone, or chalk, otherwise known as calcium carbonate, is a naturally-occurring chemical compound found in many rocks, in shells, bones, teeth and pearls.
The chemical formula of limestone is CaCO3 and it is a hard, white solid - rock hard, in fact - used for making cement, in the manufacture of glass and steel, as an ornamental and building stone, or as chalk.
If acid is dripped onto a piece of limestone, it fizzes and bubbles, leaving behind a white powder, called quicklime, and releasing carbon dioxide in a strongly-exothermic reaction.
Anne Evans
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