Sandstone
Sandstone (sometimes known as arenite) is a sedimentary rock composed
mainly of sand-sized minerals and rock grains. Most sandstone is composed of
quartz and/or feldspar because these are the most common minerals in the
Earth's crust. Like sand, sandstone may be any color, but the most common colors
are tan, brown, yellow, red, gray, pink, white and black. Since sandstone beds
often form highly visible cliffs and other topographic features, certain colors
of sandstone have been strongly identified with certain regions.
Rock formations that are primarily composed of sandstone usually allow
percolation of water and other fluids and are porous enough to store large
quantities, making them valuable aquifers and petroleum reservoirs. 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 limestone or other
rocks fractured by seismic activity.
Sandstone is mined by quarrying. It is sometimes found where there used
to be small seas. It is usually formed in dry places like the Sahara Desert in
Africa, the Arabian Desert in the Middle East and the Australian Desert including
Sydney. In the western United States and in central Australia, most sandstone
is red.
Sandstone
is converted into quartzite through heating and pressure related to tectonic compression.
