Igneous Rocks

Igneous rocks are "fire formed" rocks. Magma and lava are molten rock that when cool become a solid. Magma is liquid rock that is under the surface of the earth, while lava is magma that comes onto the surface. Granite is a common igneous rock. The rocks that form from molten earth have many small crystals that grow into each other. The crystals grow larger the longer the magma takes to cool.

Metamorphic Rocks

Metamorphic means "many changes". It forms from igneous, sedimentary, or other metamorphic rocks. It forms when a rock is under extreme pressure and heat. The metamorphic rock does not reach a melting point, otherwise it would become an igneous rock again. The heat and pressure does not change the composition of the rock, but changes the structure of the rock.

Sedimentary Rocks

Sedimentary rock forms from sediment. It is silt, sand, gravel, and other forms of sediment from the erosion of igneous, metamorphic, or other sedimentary rocks. Sediment can also be a mineral solution in water. The sediment settles into a basin or valley, then becomes solidified (with or without standing water). Sandstone forms when rainwater passes through the sand. Minerals drop out of solution forming a "cement", sandstone forms by this cementing. Sedimentary rocks always form in horizontal layers.