The Three Kinds of Rocks
Igneous rocks, which are also called fire rocks and are formed either underground or above ground. Underground, they are formed when the melted rock, magma, deep within the earth becomes trapped in small pockets. As these pockets of magma cool slowly underground, the magma becomes igneous rocks.
For thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn away. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer is deposited - one on top of the other. These layers, pressed down more and more through time, eventually cause the bottom layers to slowly turn into rock.
Metamorphic rocks are rocks that "morphed", or changed, into another kind of rock. These rocks were once igneous or sedimentary rocks. The rocks are under tons and tons of pressure, which builds up heat, and this causes them to change. If you look at metamorphic rock samples closely, you'll discover how flattened some of the grains in the rock are.