This sample of limestone has a large fossil in it. This happens all the time since limestone is made of shells and dead sea creatures that collect at the bottom of the ocean. They get buried by other sediment and, after millions of years of being under pressure, the particles get cemented together to form solid rock. Limestone is a very strong rock and is often cut into large blocks and used in the construction of buildings and skyscrapers. Crushed limestone is also used to make cement, plaster and chalk.
Limestone fizzes in vinegar, which means that it reacts to acids. This also means that the outsides of many of our buildings and monuments are being affected by acid rain. Acid rain occurs when large companies pollute the air by releasing chemicals like sulfur into the atmosphere. The sulfur combines with hydrogen and oxygen in the air to form sulfuric acid!