Sandstone

Sandstone is an arenaceous sedimentary rock composed mainly of feldspar and quartz and varies in colour (in a similar way to sand), through grey, yellow, red, and white. Since sandstones often form highly visible cliffs and other rock formations, certain colors of sandstone may be strongly identified with certain regions. For instance, much of the North American West is well-known for its red sandstones.

Origins

Sandstones are clastic in origin (as opposed to organic, like chalk or coal). They are formed from the cemented grains that may be fragments of a pre-existing rock, or else just mono-minerallic crystals. The cements binding these grains together are typically calcite, clays and silica. Grain sizes in sands are in the range of 0.1mm to 2mm. (Rocks with smaller grainsizes include siltstones and shales and are typically called argillaceous sediments, as are also clays. Rocks with larger grainsizes include both breccias and conglomerates and are termed rudaceous sediments.).

Related Topics:
Calcite - Clay - Silica - Siltstone - Shale - Breccia - Conglomerate

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The principal mechanism for the formation of sandstone is by the sedimentation of grains out of a fluid, such as a river, lake or sea. The environment of deposition is crucial in determining the characteristics of the resulting sandstone, which on a finer scale include its grainsize, sorting, composition and on a larger scale include the rock geometry. Principal environments of deposition may be split between terrestrial and marine, as illustrated by the following broad groupings:

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• Terrestrial environments
• Rivers (levees, point bars, channel sands)
• Lakes
• Marine environments
• Shoreface sands
• Deltas
• Turbidites (submarine channels)