[.................At present the wonders of sand will be presented via text only. Later, I will download photos of sandy beaches, desert sands, etc............................................................]
SANDS OF TIME
"Sand," Rachel Carson tells us, "is a substance that is beautiful, mysterious, and infinitely variable, each grain on a beach is the result of processes that go back into the shadowy beginnings of life, or the earth itself." There is nothing particularly striking about a grain of sand, unless, of course, you have the misfortune of having one blow into your eye. Then the speck that seems so benign and innocuous reveals its true character as a descendant of the great rocks of the world.
But to sedimentologists, geologists, and paleogeographers, the size, shape, roundness, surface texture, and composition of a single grain of sand tell the story of forces that pried it from its matrix and brought it to the shore. If one sifts through a handful of sand, and looks closely at the grains, it is possible to detect many individual shapes, sizes, and colors; these variations are even more dramatic if samples come from different beaches. Some grains are almost perfectly round and smooth, others jagged, rough, and irregular in texture and shape. Light-colored, nearly spherical sand is composed almost entirely of quartz, a common mineral from which the earth's crust is compounded. In contrast, dark sands are made up of volcanic particles and complex silicates that were spewed up from deep within the earth's core.
Nearly indestructible, a single grain of sand can be millions of years old. These fragments can be seen as the original "silicon chip," acid-etched with the story of the rise and fall of mountains, rivers, deserts, and creatures. Lilliputian messengers from the depths of geologic time, grains of sand are the bridge between past and present--the last, hardy survivors of distant islands, deltas, cliffs, mountains, and long-lost landforms. Buffeted by wind, leached by rain, bleached bone-dry by the sun, sands are also made up of the carbonate skeletons of creatures from the tepid tropical seas, and in this respect are geological cartes de visite from obscure worlds beneath the waves.
Generally ranging in size from one sixteenth of a millimeter to two millimeters--and sometimes even five millimeters--in diameter, sand is smaller than gravel but larger than silt or clay. The rich tonal variations and range of shapes emerge fully only under a microscope, where sands reveal themselves as pointed and bulbous rays exploding from pillow-shaped centers; creamy lozenges; shiny ball bearings; jagged, striated, and pitted flakes; glossy disks and striped cigars; spheres as bumpy as Trix cereal; shriveled red chiles of volcanic lavas; and crystalline green jelly beans bursting with glauconite from the ocean floor.
The mechanics of sand formation are simple. Rocks, reefs, and coral break down through either mechanical or chemical weathering, becoming smaller and smaller as they are pounded by the hydraulic or pneumatic pressure of waves. They are pried apart by ice exerting thousands of pounds of pressure per square inch, or split by the insistent probing and prying of plant roots. Heated by lightning or fire, rocks expand until they break off in chips and flakes. Or, through involved chemical processes, minerals and chemicals within the rocks-gradually decompose, and the rock literally decays as if it were an organic substance. The size of each resulting grain is determined by the kinetic intensity of the medium that transported and deposited it. A strong current or a powerful wind, for instance, tends to carry larger particles greater distances. The smoothness or the jaggedness depends on the degree of abrasion during transport. The rounder the sand, the longer it has been weathered by wind or water. By contrast, ragged grains have either not traveled far or been cushioned in their journey by an envelope of mud.
The weathering process that turns rocks into sand, however, is only half the story. The other half involves the consolidation of sands into rock during the vast intervals of geological time. The rock of ages, as it turns out, is impervious to time only in our minds. Sand that once was rock becomes rock once again as it slowly sediments and compresses into layers of sandstone, which, in turn, transmute into sand. Standing on a cliff overlooking a raging sea, we watch waves hurl themselves against the shore, scooping up cobbles at the base of the cliff and lofting them into the crown of seething foam. Then the wave retreats, hauling its load of stone along the sea bottom, until the next swell rushes in to repeat, relentlessly, the work of breaking, grinding, polishing.
In warm waters, abundant sea life provides a steady source of bone and shell fragments, from conches, clams, mussels, scallops, shellfish, corals, fish, and even microscopic plankton. Most of the fabled white beaches of the world are in fact the burial mounds of such sea life. Radiocarbon dating shows that the sand of Miami Beach, for example, is on average thirteen thousand years old, with some material over thirty thousand years old. So, as we dig our toes into the soft shell sands, we quite literally burrow deep into antiquity.
Because sand is derived from a spectrum of substances, it comes in many colors--tan, yellow, white, pink, purple, red, blue, green, gray, and black. The precise shade of each grain depends on the rock or organism from which it came. To a great degree, color alone can identify the origin of a beach with reasonable accuracy. Armed with a strong hand-lens, an experienced geologist can readily distinguish between translucent, light-colored grains of quartz and brown, dullish feldspar, and then link these properties to the geological history of a specific beach type.
Delivered to their site long ago by slowly moving glaciers, the whitish beach sands of the Northeastern United States are mainly mineral in origin. As one moves farther south--to North Carolina, let's say--the sand begins to take on the pinkish and pale-yellow hues of crushed seashells. Florida's eastern flank is rimmed with coarse grains of quartz, but the tip and the western shore are covered with sand the color and feel of uncooked semolina. Along the Gulf Coast, the fine-textured beaches blend the rosaceous tint of pulverized shrimp and conch with the white, yellow, and orange colors of minerals--copper, calcium, and quartz--carried there by rivers from the Appalachian highlands and the Great Plains.
As one moves farther south and west, beach sands begin to broadcast a flashy, south-of-the-border exuberance characterized by the paintbox tints of tropical seas. The brilliant white of Bahamian beaches is derived from the precipitated oolites or calcium-carbonate coating on bits of coral and whelk. Bermuda's pink sands blush with the calcite of limestone, coral, and shell. The gray sands of St. Lucia's southwestern rim, on St. Kitts, Saba, and Domenica--all in the Caribbean--bespeak a volcanic origin. In fact, the mixture of vanilla-colored shell and coral beaches and dusky volcanic sands is a formula repeated throughout the tropics. This pangeological recipe is evident in the golden coral beaches of the Seychelles in the Indian Ocean, the mauve-and-purple sands of Fiji's Taveuni Island, and in Queensland's kaleidoscopic blends of ground-up shells from the Coral Sea. The striking hues of Hawaii's shores--the olivine green of Papa-kolea Beach, the cinder-cone red at Hoku-'ula, and the jet black of Polulu Beach--also derive from volcanic eruptions, rather than decomposing sea life.
As one travels north into the temperate zone, the color palette of beach sand fades in vibrancy. On the eastern coast of England, the pockets of sand deposited among the shingle are, like the rock from which they have eroded, light gray. By contrast, the northern coast takes on an almost honeyed hue. Along the northeastern coast of Wales, the golden beaches have a faintly rosy cast. All along the Baltic, the dunes and berms are a soft tan. Mediterranean beaches--the Costas del Sol, Calida, Blanca, Dorada and Brava, as well as the strands on deltas of the rivers Rhone, Arno, Po, and Brenta--range from puce to whitish gray, reflecting the tints of clay, mud, and river sand transported from deep inland. Up and down the Cote d'Azur, along Italy's southern coast, and on the shores of Alexandria, the pale sand flashes an occasional grain of marble, glass, or alabaster that centuries ago was part of some ancient Roman villa. By and large, the meager sands of Mallorca, Sicily, Sardinia, Corsica, and Cyprus--and of other islands in the Adriatic and the Aegean--are coarse, lacking the sustained buffeting of rough winds and waters.
Along the Sea of Cortes and on the Pacific coast of Baja California, the beaches still sparkle with coarse-grained sand colored the buff of desert rock, the white of marlin bones, and the burnt sienna of weathered coral. But along the beaches of the Pacific Northwest, tan and gray predominate. Descended from basalt cliffs that were extruded as sea-floor lavas several million years ago, these sands glisten like oil slicks when wet. The brownish specks scattered among them come from the quartz and feldspar of granites that were spot-welded to the Rocky Mountains of the North American continent, and then spilled down the tributaries of the Columbia River, before draining into the Pacific. Other mighty rivers--the Orinoco, the Amazon, and Argentina's Colorado--enrich ocean sands with grains of gold, platinum, and uranium, to which is added the glint of garnets and emeralds.
In certain beaches, sand exhibits another remarkable property, neither useful nor threatening, but aesthetic. These sands "sing" and "bark," as though they were endowed with vocal cords, although in this instance the musical sounds are produced by the gentle friction of grain against grain. In Kauai, Hawaii, a golden knot of windblown dunes in the shadow of the opal-tinted cliffs of Polihale produce cries in various cadences. In the wind, they rustle like silk; when someone slides down them, they bark like dogs.
Still intriguing scientists, singing sands have been threading through the literature of explorers and travelers for over a thousand years, posing the riddle of their vocalization. Some say the sound is produced by the friction of sand against sand that has been coated with dried salt, much as the violin's melody is produced by the action of resin on the bow. Others speculate that the thin layers of gas which are released between the grains act as percussive cushions capable of considerable vibration and tone production.
Balefully sibilant "singing sands" have been discovered in England and Wales. On the Isle of Eigg, in the Hebrides, the snowy sand at the base of sandstone cliffs gives off an eerie whining. The sands of Oregon's Florence Beach squeak with the high-pitched bark of distant chihuahas. But perhaps the most fabled of these are commemorated in the Arabian Nights, which lauds the weird beauty of the sands skirting the Mountain of the Bell, the Jebel Nagous of the Isthmus of Suez. When whipped up by storm winds, these sands chant and groan like deep organ notes; on calm days, they tinkle like bells.
(C) 1998 Lena Lencek and Gideon Bosker All rights reserved. ISBN: 0-670-88095-7
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