<Ul> <Li> Sedimentary rocks are formed through the gradual accumulation of sediments: for example, sand on a beach or mud on a river bed . As the sediments are buried they get compacted as more and more material is deposited on top . Eventually the sediments will become so dense that they would essentially form a rock . This process is known as lithification . </Li> <Li> Igneous rocks are rocks which have crystallized from a melt or magma . The melt is made up of various components of pre-existing rocks which have been subjected to melting either at subduction zones or within the Earth's mantle . The melt is hot and so passes upward through cooler country rock . As it moves, it cools and various rock types will form through a process known as fractional crystallization . Igneous rocks can be seen at mid ocean ridges, areas of island arc volcanism or in intra-plate hotspots . </Li> <Li> Metamorphic rocks are rocks which once existed as igneous or sedimentary rocks but have been subjected to varying degrees of pressure and heat within the Earth's crust . The processes involved will change the composition and fabric of the rock and their original nature is often hard to distinguish . Metamorphic rocks are typically found in areas of mountain building . </Li> </Ul> <Li> Sedimentary rocks are formed through the gradual accumulation of sediments: for example, sand on a beach or mud on a river bed . As the sediments are buried they get compacted as more and more material is deposited on top . Eventually the sediments will become so dense that they would essentially form a rock . This process is known as lithification . </Li> <Li> Igneous rocks are rocks which have crystallized from a melt or magma . The melt is made up of various components of pre-existing rocks which have been subjected to melting either at subduction zones or within the Earth's mantle . The melt is hot and so passes upward through cooler country rock . As it moves, it cools and various rock types will form through a process known as fractional crystallization . Igneous rocks can be seen at mid ocean ridges, areas of island arc volcanism or in intra-plate hotspots . </Li> <Li> Metamorphic rocks are rocks which once existed as igneous or sedimentary rocks but have been subjected to varying degrees of pressure and heat within the Earth's crust . The processes involved will change the composition and fabric of the rock and their original nature is often hard to distinguish . Metamorphic rocks are typically found in areas of mountain building . </Li>

What processes are involved in the formation of igneous rocks
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