Wednesday, July 4, 2012

July 2012 Rock of the Month


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.