Sandstone:Layers of History
by Kate Parrott
Sandstone is a sedimentary rock, which derives its name from the sand-sized minerals or grains that account for its composition. Most sandstone is composed of quartz and feldspar, two of the most common minerals in the Earth's crust. Some of the other common minerals in sandstone, which account for the rock's hardness, include silica, carbonates, clay and iron oxides.
Formation of sandstone usually occurs offshore from river deltas, but desert dunes and beaches can leave sandstone beds as well. Two main groups account for sandstone's environmental deposits: terrestrial deposits, coming from rivers, channel sand point bars and lakes; and marine deposits, from shoreface sands, deltas and submarine channels.
The rock's formation occurs in two phases: The first is sedimentation, where layers of sand accumulate via water or air; the second is compaction, which occurs when pressure is exerted from overlaying materials and precipitation within the pore spaces between the sand grains. Sandstone is formed in layers and, over time, the layers become compacted until the bottom layers slowly turn into rock.
There are three types of sandstone: arkosic, quartzose and argillaceous. Arkosic sandstones have a high feldspar content ? more than 25 percent ? and a composition similar to granite. Quartzose sandstones have a high quartz content ? approximately 90 percent consistency. Argillaceous sandstones have a high clay or silt content and a very fine consistency.
Quarries of Sandstone
Sandstone is quarried around the world, from India and Australia, to Canada, Egypt and the United States. In the United States, it is quarried widely, including New York, Idaho, Minnesota, Pennsylvania, West Virginia, Iowa, Wyoming and Kansas.
Sandstone is mined by a process of digging, blasting or cutting. After it is excavated, it is dressed, cut, sawed, surface grinded, polished and edge cut.
Colors of Sandstone
The color of sandstone is extremely varied and depends on the quantity and color of the cementitious materials present and the overall color of the mineral grains. Sandstone spans the full spectrum of colors, ranging from sandy yellows to deep golds, pale pinks and light greens.
Light colors generally result from the absence of cementitious materials, or joined by calcite or quartz. Buff, brown and red colors result from the presence of limestone and hematite. Greensand, a type of green sandstone, results from the presence of glauconite.
Applications of Sandstone
Sandstone is available in tiles, slabs and blocks, in finishes ranging from natural and calibrated, to honed, polished and flamed. Sandstone is a very versatile material, applicable for most types of interior and exterior applications, including wall cladding, roofing and flooring.
Sandstone also has a long history in the building industry. The stone generally has a uniform texture and it is somewhat soft, making it a user-friendly stone for a variety of applications. It is favored for wall claddings because of its low absorption rate, high compression strength and aesthetically pleasing appearance. Its appearance and high durability make it ideal for flooring as well. With a variety of colors and finishes, it is also easy to match it to nearly any décor.
The stone is a common paving material because it can be highly weather resistant. As a paver, sandstone is prized for its ability to maintain age and appearance over time, as well as for the different dimensions available. Sandstone pavers can be used for patios, pool surrounds, pool coping, balconies, as well as cladding and veneer.
Sandstone has been used in some of the world's most famous structures, including the White House, the Taj Mahal, the pyramids and the Angkor Vat, and ancient Cambodian temples
To build the White House, the particular sandstone used was discovered to be highly porous and susceptible to water damage. Therefore, masons had to coat the building in a wash of salt, rice and glue, giving the building its first coat of white paint and coining the name "White House."
In Australia, Ayers rock, or Uluru, is a vast outcropping of sandstone rising 986 feet in height and spanning five miles around. Ayers rock is located in Kata Tjuta National Park and is owned by the local Aboriginals. Depending on the time of day, the rock can change colors from blue or violet to glowing red.