Limestone is a whitish to yellowish stone that often contains fossils.   It was formed when animals with shells died and their shells settled to the bottom of ancient seas.  As these shells were buried deeper and deeper they were compacted into limestone. They are locked together like the pieces of a 3-Dl jigsaw puzzle.  This gives the limestone strength without being cemented together.

        It is found worldwide.  Some islands are composed of mostly limestone. There are many limestone formations in different parts of the United States.

Limestone is used as an ingredient of cement and in blackboard chalk.