Rock Formations Around The World

The three main ways rocks are formed:
• Sedimentary rocks are formed through the gradual accumulation of sediment: for example, sand on a beach or mud on a river bed. As the sediment is buried it is compacted as more and more material is deposited on top. Eventually the sediment will become so dense that it is essentially rock. This process is known as lithification.
• 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.
• 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.