How are rocks made?

Rocks are found almost everywhere.  Very small rocks are called sand.  Rocks bigger than sand have other names, like pebbles, or stone.  Big rocks are called boulders.  In fact, almost all the earth – the mountains and the ground itself – is made of rock.

Rocks are made of minerals.  A few are made of just one mineral, but most rocks are made of many minerals, of magma, that lies under the earth’s crust.  As the magma pushes to the surface of the earth.  It cools and hardens into such rocks as granite, basalt and lava.

Some rocks are formed from bits and pieces of older rocks that pile up in layers and harden into rocks we know as sandstone and limestone.  Still other rocks began as one kind of rock and later were changed into other kinds of rocks.  Some limestone, for example, was changed by hear and pressure deep down in the earth into marble.