Download An Igneous rock can be either intrusive or extrusive, it is cased by

An Igneous rock can be either intrusive or extrusive, it is cased by partial melting of
existing rocks, this magma then migrates towards the surface, if it reaches the surface it
will be erupted in a volcano. Basalt is an example of such a rock. If it doesn't reach the
surface it will still cool into rock, but the process will take longer and the rock formed
will have bigger crystals, granites and gabbros are both examples of such rocks.
Sedimentary rocks are formed from pieces of other rocks or from biological sediments.
A sandstone is an example of the former and a limestone such as chalk one of the latter.
Pressure is not required to turn a sediment into rock although it can increase the solidarity
of the rock. What does turn unconsolidated sediments into rock is the growth of cements,
new minerals form around the grains and slowly stick the rock together. You can often
find an example of this on a sandy beach just above the high tide line.
Metamorphic rocks can be both igneous or sedimentary in origin, but they have been
subjected to high temperature, or pressure, or both. By burial or proximity to magma.
Marble is an example of a metamorphosed limestone.