THE ROCK CYCLE

IGNEOUS ROCK

Deep in the earth's crust thereare places where the rock hasmelted into magma which is a mixture of crystals and liquidrock. Sometimes the magmaerupts out of the earth througha volcano and then it is calledlava. When the lava cools andhardens on the earth's surface,it is called volcanic igneousrock. If the magma cools andhardens under the ground, it iscalled plutonic igneous rock.

SEDIMENTARY ROCK

Wind and water cause erosion,breaking off pieces of rock andcarrying them from one placeto another. Gradually thesepieces along with sand, pebbles, shells and plant matter gather into layers called sediment. Over a longperiod of time the sedimenthardens into rock. That is howsedimentary rock is formed.Most of the rock on the earth'ssurface is sedimentary.

METAMORPHIC ROCK

Just as cookie dough changesas it is baked, rock changes asit is heated, squeezed or both.Rocks deep within the earthare put through intense heatand pressure. In time, theseforces change sedimentary origneous rock into another typeof rock called metamorphic rock.