SANDSTONE
Sandstone (sometimes known as arenite) is a sedimentary rock composed mainly
of sand-sized minerals or 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, and white. Since sandstone beds often form
highly visible cliffs and other topographic features, certain colors of
sandstone have been strongly identified with certain regions.
Some sandstones are
resistant to weathering, yet are easy to work. This makes sandstone
a common building and paving material. However, some that have
been used in the past, such as the Collyhurst sandstone used in North West England, have been found less resistant,
necessitating repair and replacement in older buildings. Because of
the hardness of the individual grains, uniformity of grain size andfriability of their structure, some types of
sandstone are excellent materials from which to make grindstones, for sharpening blades and other
implements. Non-friable sandstone can be used to make grindstones for grinding grain,
e.g., gritstone.
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 sea areas. It is usually formed
in deserts or dry placeslike the Sahara Desert in Africa, the Arabian desert in the Middle East and the Australian desert. In the western United States and in central Australia, most sandstone is
red.
BACK
|