Sifting through the Sands of Time

When you're on the beach, you're stepping on ancient mountains, skeletons of marine animals, even tiny diamonds. Sand provides a mineral treasure-trove, a record of geology's earth-changing processes.

 

Sand: as children we play on it and as adults we relax on it. It is something we complain about when ft gets in our food, and praise when it's moulded into 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 marine life that goes back thousands and in some cases millions of years.

 

Sand covers not just sea-shores, but also ocean beds, deserts and mountains. It is one of the most common substances on earth, And it is a major element in man made materials too –concrete is largely sand, while glass is made of little else.

 

What exactly is sand? Well, it is larger than fine dust and smaller than shingle. In fact, according to the most generally accepted scheme of measurement, devised by the Massachusetts Institute of Technology, grains qualify if their diameter is greater than 0.06 of a millimeter and less than 0.6 of a millimeter.

 

Depending on its age and origin, a particular sand can consist of tiny pebbles or porous granules. Its grains may have the shape of stars or spirals, their edges lagged or smooth. They have come from the erosion of rocks, or from the skeletons of marine organisms, which accumulate on the bottom of the oceans, or even from volcanic eruptions.

 

Color is another clue to sand's origins. If it is a dazzling white, its grains may be derived from nearby coral outcrops, from crystalline quartz rocks or from gypsum, like the white sands of New Mexico. On Pacific Islands jet black sands form from volcanic minerals. Other black beaches are magnetic. Some sand is very recent indeed, as is the case on the island of Kaomagma in Hawaii, where a beach was created after a volcanic eruption in 1990, Motten lava spilled into the sea and exploded in glassy droplets.

 

Usually, the older the granules, the finer they are and the smoother their edges. The fine, white beaches of northern Scotland, for instance, are recycled from sandstone several hundred million years old. Perhaps they will be stone once more, in another few hundred million.

 

Sand is an irreplaceable industrial ingredient whose uses are legion: but ft has one vital function you might never even notice. Sand cushions our land from the sea's impact, and geologists say it often does a better job of protecting our shores than the most advanced coastal technology.