王文萍

沙子是我們生活中不可或缺的原料之一，似乎取之不竭，用之不盡，為什么現(xiàn)在會(huì)面臨沙子資源短缺的危機(jī)呢？

Tiny and unnoticeable though it may seem， sand is a critical ingredient of our lives. It is the primary raw material that modern cities are made from. The concrete needs it to construct shopping malls， offices， and apartment blocks; along with the asphalt， we use sand to build roads.

The glass in every window， windshield， and smart phone screen is made from melted?down sand. And even the silicon chips inside our phones and computers， along with virtually every other piece of electronic equipment in your home， are made from sand.

Where is the problem with that？ You might ask. Our planet is covered in it. Huge deserts from the Sahara to Arizona have made dunes（沙丘） of the stuff. Beaches on coastlines around the world are lined with sand. We can even buy bags of it at our local hardware shop for a fistful of small change.

But believe it or not， the world is facing a shortage of sand. How can we possibly be run?ning low on a substance found in virtually every country on earth and that seems essentially limitless？

Sand， however， is the most?consumed natural resource on the planet besides water. People use some 50 billion tonnes of “aggregate”（骨料）—the industry term for sand and gravel， which tend to be found together—every year. Thats more than enough to blanket the entire United Kingdom.

The problem lies in the type of sand we are using. Desert sand is largely useless to us. The overwhelming bulk of the sand we harvest goes to make concrete， and for that purpose， desert sand grains are the wrong shape. Eroded by wind rather than water， they are too smooth and rounded to lock together to form stable concrete.

The sand we need is the more angular（棱角分明的） stuff found in the beds， banks， and flood plains of rivers， as well as in lakes and on the seashore. The demand for that material is so intense that around the world， river beds and beaches are being stripped bare， and farmlands and forests are torn up to get the precious grains.

Why did the author think that we are in the crisis of sand when there is bulky sand in the world？