Sandstone is a medium-grained sedimentary rock. It is pale yellow, grey or often red to brown. Composed of rounded grains of silica (quartz) that are all the same size, it is cemented together by silica, calcite or an iron mineral.
Sandstones are often layered and can show colour variations between the layers.
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How is it formed?
Sand sized grains of quartz are produced by the weathering of other rocks. These are transported and deposited by wind, waves and rivers. The original sediment may have been a sand bank, beach or desert sand dunes.
When the sand is buried beneath other sediments it is compacted and cemented by chemicals dissolved in the water seeping through it. Sandstones formed in deserts are usually red in colour. Those formed on beaches or rivers are often yellow or grey.
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