Sedimentary rocks are formed beneath water as sediment accumulates over time and a process of cementation subsequently takes place. The accumulated sediments may be natural minerals or organic matter. The process can often be seen by the presence of visible layers in a cliff face.
The mineral quartz which is found in all rock types occurs as grains of sand in sedimentary rocks. This type of rock covers seventy five to eighty per cent of the Earth's land area. Sedimentary rocks are one of the three main types of rock with the other two being igneous and metamorphic.