| Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Sandstone may be any color but the most common colors are tan, brown, yellow, red, gray and white.
Rock formations that are primarily sandstone usually allow percolation of water and are porous enough to store large quantities, making them valuable aquifers. Fine-grained aquifers, such as sandstones, are more apt to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestones.
The formation of sandstone involves two principal stages. First, a layer or layers of sand accumulates as the result of sedimentation, either from water (as in a river, lake, or sea) or from air . Typically, sedimentation occurs by the sand settling out from suspension, i.e. ceasing to be rolled or bounced along the bottom of a body of water (e.g. seas or rivers) or ground surface (e.g. in a desert or sand dune region).
Once the sand has accumulated, then it becomes sandstone when it is compacted by pressure of overlying deposits and cemented by the precipitation of minerals within the pore spaces between sand grains. The most common cementing materials are silica and calcium carbonate, which are often derived either from dissolution or from alteration of the sand after it was buried.
Amazing stuff, sandstone!
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