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Sand

The Never-Ending Story

UNIVERSITY OF CALIFORNIA PRESS

Individuals

Birth and Character

Who could ever calculate the path of a molecule? How do we know that the creations of worlds are not determined by falling grains of sand? Victor Hugo, Les Misérables

For Nature is the noblest engineer, yet uses a grinding economy, working up all that is wasted to-day into to-morrow's creation; not a superfluous grain of sand for all the ostentation she makes of expense and public works. Ralph Waldo Emerson, "The Young American"

CONCEPTION

It was love at first sight. As the raven circled over the endless ocean, he saw a beautiful mermaid and was entranced. He flew close and asked her to marry him, and she agreed—but on one condition: "Make me some land where I can sit on a beach and dry my hair and I will marry you." The raven knew he would need help with this task and, in return for not insignificant favors but without revealing his intentions, enlisted the seal and the frog to procure some sand from the bottom of the sea. The raven then flew up into the strong winds above the ocean and scattered the grains to every corner of the world. At the place where each grain fell into the ocean, an island was formed: small islands from the tiny grains, large ones from the biggest grains. The mermaid was delighted, for the first time in her life drying her hair on a sandy beach. And then she and the raven were married.

This creation story, as told by the tribes of the Pacific Northwest whose ancestors were the raven and the mermaid, is only one example of myths from around the world in which grains of sand are the fundamental components of the Earth's creation. From the east coast of North America to the Carpathians, from West Africa to the Pacific Islands, sand is the parent for the birth of the land, a powerful symbol of origins. In The Neverending Story, the fantasy novel by Michael Ende, translated from the original German in 1983 and adapted into several films, the land of Fantasia is destroyed, with only a single grain of sand remaining. But that single grain enables the rebirth of the world.

The symbolism of sand as a foundation for our world continues in our collective subconscious, and the story of sand is indeed never-ending.

As we all know from the aftermath of a family visit to the beach, a single grain of sand can get anywhere. It physically penetrates, often to the detriment of health or a piece of machinery, and it can embed itself in our imagination. Pick up a single grain from the beach, look at it through a magnifying glass, and you have embarked on a journey taken by poets, artists, and philosophers—not to mention geologists. William Blake's "To see a world in a grain of sand / And a heaven in a wild flower," from his "Auguries of Innocence," has been put to use countless times to refer to flights of the imagination (the more gloomy direction that the poem subsequently takes is often ignored). Echoing Blake, but in perhaps a more approachable vein, Robert W. Service wrote, in "A Grain of Sand":

For look! Within my hollow hand,
While round the earth careens,
I hold a single grain of sand
And wonder what it means.
Ah! If I had the eyes to see,
And brain to understand,
I think Life's mystery might be
Solved in this grain of sand.

What is it about the idea that within its minuteness a grain of sand encapsulates greater things, that it is a metaphor for a grander scale, that it has a story to tell? There is a temptation to anthropomorphize, to gaze into the weather-beaten face of a sand grain and see ourselves reflected, our own life stories, our own journeys, our own worlds, to see the grain as an individual with a character, as well as a member of a family and larger clans, extended global tribes. Anthropomorphizing, yes, but it does provide a deep resonance and a framework within which to scrutinize a grain of sand. The birth of a sand grain is a microcosmic event, a flap of a butterfly's wings heralding greater change and a larger creation. Each grain carries the equivalent of the DNA of its parents and develops a character through its life that is molded partly by its parentage, partly by its environment. Compared to the scale of a human life, however, the sand grain's story is never-ending, and rebirth is a regular event.

BIRTH

In order to read the stories hidden in a grain of sand, we need to look at its exterior and interior, to take it apart. Like people, each sand grain is unique but belongs to a particular family with common genetics and origins. Just as stories are told in different languages and emerge from different cultures, sand can be created in different ways and can be composed of a wide variety of substances, although there is one dominant group in the population that shares a common history and a common chemistry.

Sand can be made by simply grinding up rocks into smaller and smaller pieces, but this is not easy and only glaciers do it effectively. Sand can be made biologically, from small shells and other products of the living world; whole beaches are formed this way. Warm seas can deposit their dissolved minerals, like limescale in a kettle, making minute pellets of sand. Sand grains can originate cataclysmically, as when molten rock spewed from a volcano chills and shatters in the air, or as the surface of the Earth melts under the impact of a meteorite, ejecting cascades of liquid droplets into the atmosphere; these solidify and shower back across oceans and land to be found as individual grains within sand or sandstone. But by far the majority of sand grains are made of one of the Earth's most common ingredients, the mineral quartz, and are formed by the process that works, day in, day out, on every exposed piece of land on the Earth's surface—weathering.

The most common element in the crust of the Earth and in the land around us is oxygen. Not as the gas that we need to survive, but chemically bound up with other elements to form solid—and not-so-solid—minerals, just as sodium and chlo- rine join forces to make salt. The second most common element is silicon, which teams up with oxygen and other common elements, such as aluminum, iron, magnesium, potassium, and sodium, to make the dazzling variety of minerals that are the ingredients of most of the Earth's crust—the silicates. One family of these minerals, the feldspars, is the most common constituent of the crust. But silicon and oxygen themselves make a fine couple, strong and enduring: together, they form the mineral quartz, the common form of silica. Close to 70 percent of all the sand grains on the Earth are made of quartz—tiny crystal balls, each with its own revelations.

Born in the cauldron of the molten depths of the Earth's crust, igneous rocks, cooled and solidified in a glittering matrix of crystals, are out of their element when they are ultimately jacked up by tectonic forces and exposed at the Earth's surface. However hard and durable they may seem, rocks such as granite are vulnerable to the weather, many of their constituents chemically unstable. The ravages of time and the elements are obvious on old gravestones and buildings—the corrosion of Cleopatra's granite needles is the classic example. In the midst of that corrosion, sand grains begin to sense freedom.

Chemistry and acidic rain are prime actors in the drama of weathering, but they are not the only members of the cast. Temperature changes, expansion and contraction, freezing, thawing, and the chemistry of water all work away at cracks, even in arid climates. And plants have leading roles, too. Not only does the merciless growth of roots physically tear open the fractures, as in the old tree-lined sidewalks of so many towns, but the roots are chemically active. They do, after all, feed the tree. In conspiracy with minute fungi, the roots extract ingredients essential to the plant's growth—removing them from the minerals among which the roots have worked their way, and removal weakens the rock. It doesn't take mighty trees to accomplish this—humble lichens and algae effectively rot, slowly but surely, the rock on which they live.

All rocks, even the tough ones, like granite and its relatives, rot. The weakest links in the chain are the first to go, and in a granite these are the feldspar crystals and their fellow silicates. Quartz is made of sterner stuff, thanks to its internal structure. In a quartz crystal, the average composition is one silicon atom for every two oxygen atoms, but there is no such thing as an SiO2 molecule: the silicon and oxygen conspire together to construct incredibly strong chains of pyramids, and the chains interlink—like DNA—in long helix-shaped spirals. This structure is almost impregnable—quartz is a survivor, hard, resistant, and extremely difficult to dissolve. In granite, each crystal of quartz is surrounded by weaker neighbors; other minerals, originally formed under more extreme conditions, are more vulnerable and unstable at the Earth's surface: they corrode rapidly. Feldspars rot away to form clay (the granites of Dartmoor decay to provide the vast deposits of "china clay" historically vital to the ceramics industry). Support for the quartz grain vanishes and, like a loose tooth, it drops out of the rock. A sand grain has been born.

Rotted, corroded, fragmented, pulverized. Comminuted. The ultimate fate of the toughest rocks is to be broken into pieces, clasts (from the Greek klastos, "broken"). The feet of the towering cliffs of Yosemite are draped in the detritus of granite simply falling apart. "The mine which Time has slowly dug beneath familiar objects is sprung in an instant; and what was rock before, becomes but sand and dust" (Charles Dickens, Martin Chuzzlewit). The sand grain has become a symbol of impermanence and the fragility of our—and nature's—works.

The birth of a sand grain in this way signifies the death of a mountain. The rocky outcrop from which it fell is now infinitesimally smaller. But the effects accumulate. It has been estimated that on the order of a billion sand grains are born around the world every second; add up these seconds over the billions of years of the Earth's history and the scale of change that erosion can cause is clear. But we can also see it happening every day on our time scale. Dramatic changes can happen overnight, as when the Associated Press reported that "New Hampshire awoke Saturday to find its stern granite symbol of independence and stubbornness, the Old Man of the Mountain, had collapsed into indistinguishable rubble" (May 3, 2003). The average effects of these processes over the Earth's surface are difficult to measure, but typically the landscape of a mountain range will be lowered by a few millimeters, a tenth of an inch or so, every year, year in, year out. The processes of weathering and erosion are immensely complex and difficult to measure. The very term weathering is probably misleading, since the rate at which it happens does not correlate clearly with weather or climate. It is apparent that much of the corrosive chemistry happens below the surface, where rocks are saturated with water moving through fractures large and small, eating away between the mineral grains. But the effects are there for all to see.

Of course, weathering eats away at everything exposed to the elements, not just granite. Sand grains originally born from granite long ago may accumulate, be buried, and become naturally glued together, lithified (from lithos, Greek for "stone" or "rock"), into a solid clastic sedimentary rock, a sandstone. When this, in its turn, is exposed at the surface, it is attacked by weathering and the sand grains are liberated again. The whole process is cyclic, over and over again, each time the grains carrying with them microscopic evidence of their parentage, their genetic origins. The majority of quartz sand grains are derived from the disintegration of older sandstones; perhaps half of all sand grains have been through six cycles in the mill, liberated, buried, exposed, and liberated again—as observed by Emerson in the opening of this chapter, reborn repeatedly.

THE IMPORTANCE OF SIZE

Our sand grain, newly born, finds itself, together with a motley collection of other detritus, organic and inorganic, as part of a soil, the in situ accumulation from the physical, chemical, and biological processes at work in a particular place. The sand grain is anonymous, waiting for rain and wind to sweep it away on an endless journey, to demonstrate its durability while its weaker companions fall by the wayside. But it is called sand not because of what it is made of or its origins, but because of how big it is.

Sand is somewhat like beauty—we know it when we see it, or touch it, but it seems difficult to describe. However, if we are to understand it, to use it, to live with it, then we have to tackle this problem. A U.S. geologist, Chester K. Wentworth, took on the task in the early twentieth century. The first sentence of his publication on describing sand reads: "In no other science does the problem of terminology present so many difficulties as in geology."

What Wentworth set in place was the concept that the only thing that matters is particle size: composition is irrelevant. This has proved an enduring and important approach. The behaviors of anything made up of relatively hard bits and pieces of a particular size, regardless of what the bits and pieces are made of, are unique and, in the case of sand, quite odd. The sugar in your teaspoon, poised over your cup of coffee, is, technically, sand. In the coffee it may not last long, but if you poured it over the kitchen floor and began blowing over it, you could begin to make sugar dunes. The salt in your salt grinder starts off as coarse sand and, when you grind it, becomes fine sand. It may dissolve in the saucepan, as does the sugar in the coffee, but until it does, it's sand. Indeed, there is a desert with massive glistening white windblown dunes made of something very much like salt: the dunes of the White Sands National Monument, in New Mexico, are made of crystals of the calcium salt gypsum, formed from the evaporation of desert lakes—but the sand grains dissolve when it rains. And along the shores of the lowest point in Africa, Djibouti's Lake Assal, the water is so saline that the sand is made of salt crystals.

So, size is what matters. But how to define size? Sand grains come in a variety of shapes, which can make measuring size quite tricky. Think of tomatoes. How would you measure the size of a tomato, compared to another tomato? Certainly, many are roughly spherical, but they are also commonly rather wrinkled, some with deep and contorted folds; some are more pear-shaped, and some are obviously oval, with some of these being essentially long and thin. What they taste like—what they are made of—doesn't matter in this instance; it's simply a question of describing their size, and how is this done among objects with such varied forms?

The idea of measuring size works well only for regular objects, the obvious examples being spheres and cubes. The diameter of a sphere or the length of the side of a cube defines each one. But for an irregular object, its size depends on how we measure it. In turn, how we choose to measure it depends on why we want this information. Why should we want to describe the size of sand grains? From a scientific point of view, we want to understand, for example, how dunes form and what determines the shape of a dune in a particular place at a particular time. How do dunes move? How do sand grains get picked up and hurled around in a sandstorm or in a flash flood in the mountains? How do water and air compare in their ability to move materials of different sizes? We are interested in why rivers form the meandering shapes they do, and how the sandbars of ancient rivers from hundreds of millions of years ago are preserved and what they can tell us about conditions on our planet back then: all good geological science. But measuring the size of sand grains can also be important on a day-to-day, more "practical" level. The size of the sand in concrete or tarmac makes a difference to its strength and other properties; when sand is used as a filter, the size, and the range of size, of the grains is fundamental. Much of our water supply comes from underground sands whose grain size determines how much we can extract and how much will be replenished. How effectively we can maintain harbors, dams, rivers, and coasts depends on our understanding of sand movement, and movement depends on size. Measuring the size of a sand grain is critical to a surprising number of aspects of our daily lives.

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Excerpted from Sand by Michael Welland. Copyright © 2009 Michael Welland. Excerpted by permission of UNIVERSITY OF CALIFORNIA PRESS.
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