Sand on the beach looks very different from sand under a microscope.
"Little drops of water, little grains of sand, Make the mighty ocean, and the pleasant land,"
reads a well-known inspirational poem by Julia Carney. However, drops of water and grains of sand can be a study unto themselves. Seen with the naked eye, individual sand grains are so small as to appear featureless. If these are placed under a microscope, a viewer can evaluate the sand and see much about its history and origins.
Size
Sand is a very specifically defined material and one of the basic types of soil. At a top particle size of 4.75 millimeters and a lower size of 75 microns (0.075 millimeters) in diameter, it's finer than gravel but coarser than silt or clay. For a sample to be classified as sand, more than 50 percent of its particles must fall in that size range. A metric ruler slid into the edge of the viewing field allows such small measurement.
Composition
Studying sand under a microscope can reveal its composition. In general, sand is composed of quartz crystals. In some beach and shoreline sands, calcium carbonate from crushed coral and broken shells may dominate, or the source may be volcanic basalt from lava flows. The bright white dunes of White Sands, New Mexico are composed mainly of gypsum. Some sands may be the result of wind-worn sandstone, which means the sand has been released from its chemical binding and returned to its original state before it was compressed into stone.
Texture
The microscope will reveal the texture of individual grains of sand. They may be jagged or smooth. The more they rub against each other or against something else, the more rounded they become. Sand blown about by the wind or moved by water will smooth the grains. The grains of beach sand are polished by the tumbling action of the waves, and even shell fragments will wear down under this constant friction. Very fine or "sugar" sand found on the beaches of Padre Island, Texas, squeaks when walked on and tends to cling to the human body and accumulate in skin folds. Coarser coral sand from a tropical strand such as Shoiaba Beach near Jeddah on the Red Sea coast of Saudi Arabia, crunches underfoot and drops cleanly off the skin after drying with a casual shake.
Color
Under the microscope, sand that appears one color en mass can show many colors. The color of sand is determined by minerals in its source. Beige, tan or light brown sand commonly originates from granite. White sand owes its color to clear quartz crystals or coral fragments. Volcanic rocks can produce many colors of sand, including red (Kaihalulu, Hawaii) and green (Papakolea, Hawaii). Black sand is found in volcanic areas of Alaska, California, Hawaii and Iceland. Pink sand is not uncommon on tropical beaches, including the islands of the Caribbean and South Pacific, but also occurs at Zion National Park's wind-deposited Coral Pink Sand Dunes.
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