Sedimentary
These rocks are formed from sand, shells and pebbles. All the particles (sediment) gather together which forms rock. Although it forms rock, it can be soft and easily break apart. .
Examples - conglomerate and limestone.
Metamorphic
Found under the surface of the earth. The rocks are formed by minerals slowly grown over time and may contain some crystals.
Examples - gneiss and marble.
Igneous
Formed when magma cools and hardens. The magma can cool inside the earth or if it erupts from volcanoes. When lava cools very quickly, no crystals form and the rock looks shiny. Gas bubbles can be trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock.
Examples - basalt and obsidian.
How do the rocks change?
Heat and Pressure.
Movements in the earth cause the rocks to go deeper under the surface of the earth. Temperatures can are so high the rocks can melt however, before melting the rocks change while in a solid state — changing from one type of rock to another.
The pressure in the earth also contributes to the change in rocks. Heat and pressure usually work together
to alter the rocks under the earth's surface which is called metamorphism, which results in metamorphic rock.
