How are Igneous, Sedimentary and Metamorphic rocks formed?
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 s
