Types of Rocks ...

Sedimentary - Sedimentary rocks are made when sand, mud and pebbles get laid down in layers. Over time, these layers are squashed under more and more layers. Eventually, the layers are lithified – turned to rock. Sedimentary rocks can be formed in deserts , lakes, rivers  and seas . 
            

Igneous - Igneous rocks are formed by solidification of cooled magma (molten rock) either below (plutonic) or above (volcanic) the surface of the earth.

The magma consists of partial melting of pre-existing rock and can be caused by one or a combination of; an increase in temperature, pressure changes, change in composition.

Metamorphic - Metamorphic rocks are made by either heating up or squashing the earth's crust. They are often found in mountainous regions. One example is slate. Slate was originally a black mud laid down on the bottom of the sea or lake. Fossils  can sometimes be found in it but they are often squashed. Other common metamorphic rocks are called marble, gneiss, schist.