Limestone is made up of mainly calcium carbonate (CaCO^3).
There are two other forms of limestone: marble and chalk. The three different types of marble can be differentiated from by their hardness. Marble is strong, limestone is slightly crumbly and chalk is very crumbly.
When limestone reacts with acid the gas formed is carbon dioxide. When mildly acidic rainwater reacts with the limestone used in a building the gas sulphur dioxide is formed.
Limestone can be used for many things for example:
-Toothpaste (to neutralize the acid in your stomach)
Why is limestone so commonly found in buildings?
Because it is strong and easy to cut into blocks easily used for buildings and can be found all over the world. Although it does have it's disadvantages as it reacts with acid.
When limestone is heated it forms quicklime and carbon dioxide.