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Sand: as children we play on it and as adults we relax on it. It is something we complain about when it gets in our eyes on a windy beach, and praise when it is made into sand castles.
But we don’t often look at it. If we did, we would discover an account of a geological past and a history of sea life that goes back thousands and, in some cases, mil- lions of years.
Sand covers not just seashores, but also ocean beds, deserts
and mountains. And it is a major element in manufactured products too - concrete is largely sand, while glass is made of little else.
Well, it is larger than fine dust and smaller than shingle. In fact, according to the
most generally accepted scheme of measurement, grains can be called sand if their diameter is greater than 0.06 of a millimetre and less than 0.6 of a millimetre. Depending on its age and origin, a particular sand can consist of tiny stones or porous grains through which water can pass. They have come from the breaking down of rocks, or from the dead bodies of sea creatures, which collect on the bottom of the oceans, or even from volcanic eruptions.
If it is a dazzling white, its grains may come from nearby coral, from crystalline
quartz rocks or from gypsum, like the white sand of New Mexico. On Pacific Islands, jet black sands form from volcanic minerals. Other black beaches are magnetic and are mined for iron ore. It washes rock into streams and rivers and down to the sea, leaving be- hind
softer materials. By the time it reaches the sea, the hardest rocks remain but every- thing else has been broken into tiny particles of 0.02 millimetre diameter or less. The largest pieces fall to the bottom quickly, while smaller particles float and settle only slowly in deeper water, which is why the sandy beach on the shoreline so often turns to mud further out.
If the individual fragments still have sharp edges, you can be sure they were
formed fairly recently. This is the case on the island of Kamoama in Hawaii, where a beach was created after a volcanic eruption in 1990. Molten lava spilled into the sea and exploded into glassy droplets. It seems that when the poet William Blake saw infinity in a grain of sand he was not far wrong. Sand is an irreplaceable industrial ingredient which has many uses. Sand cushions our land from the force of the sea, and geologists say it often does a better job protecting our shores than the most advanced coastal technology.
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