| Abstract from DBPedia | Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class of soil or soil type; i.e., a soil containing more than 85 percent sand-sized particles by mass. The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz. Calcium carbonate is the second most common type of sand, for example, aragonite, which has mostly been created, over the past 500 million years, by various forms of life, like coral and shellfish. For example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean. Somewhat more rarely, sand may be composed of calcium sulfate, such as gypsum and selenite, as is found in places like White Sands National Park and Salt Plains National Wildlife Refuge in the U.S. Sand is a non-renewable resource over human timescales, and sand suitable for making concrete is in high demand. Desert sand, although plentiful, is not suitable for concrete. 50 billion tons of beach sand and fossil sand is used each year for construction.砂（すな、英: sand）は、砕屑物のうち、礫とシルトの中間（粒径が2 ミリメートル (mm) - 1/16 mm (62.5マイクロメートル (µm)) の粒子）のものをいう。岩石が風化・侵食・運搬される過程で生じた岩片や鉱物片などの砕屑物（砕屑性堆積物）から構成され、サンゴ・貝殻などの石灰質の化石片を含むこともある。砂漠、河川の下流、河口、海岸、海底など、様々な下で観察される。 また、岩石を人工的手段で破砕した破砕物のうち、上記定義に該当する粒度のものを指す場合もある。 (Source: http://dbpedia.org/resource/Sand) |
