The secrets that a simple grain of sand reveals to us

The name itself is misleading, as it refers only to the form that rocks, minerals, organic materials and other substances take: that of small, loose grains, between 1/16 of a millimeter and 2 millimeters in diameter. Granules smaller than that size are called silt, while larger ones are called gravel. Sand is found in deserts, river beds and oceans and, of course, on beaches. Its most common component is silicon dioxide in the form of quartz, which is not strange since silicon and oxygen are the most abundant elements in the Earth’s crust, and quartz is the most abundant mineral along with another important component of the sand, feldspars, which are a class of potassium, sodium and calcium aluminosilicates.

There are more elements, of course. Sand includes skeletal remains of various organisms, including complete shells of some tiny mollusks, fragments of granitic rocks, oceanic volcanic, sedimentary and clastic rocks (agglomerations of fragments or clasts of other rocks and minerals), pieces of coral, and much more.

Thousands of kilometers

Sand comes from all types of locations and environments. It is formed when rocks break down due to the action of weathering over thousands and even millions of years. Each small grain of sand can be a traveler that has traveled thousands of kilometers since it separated from its parent rock in the times of the dinosaurs until it reached our hands, traveling in rivers, increasingly disintegrating due to the effects of water and weather. wind, waves, tides, the action of animals and plants.

The quartz that makes up most of the sand can be white, yellowish or reddish, a product of different amounts of iron oxide in its composition. Feldspars, for their part, are generally in shades between pink and brown, although there are white, gray and blue ones. Black sand comes from eroded volcanic rocks such as lava and basalt, and is usually found on beaches near areas with active volcanoes such as the Canary Islands, Hawaii and the Aleutian Islands.

There are also beaches, like those of Bermuda, whose pink color is due to the shells of single-celled organisms called foraminifera, while the white beaches of Hawaii practically lack quartz, because they are the product of the depositions of parrot fish, which bite. and they scrape the auks from rocks and dead corals, take their nutrients and excrete the calcium carbonate that forms the skeleton of the corals in the form of fine sand.

under the microscope

Putting a handful of sand under the microscope is a wonderful adventure that every child, even every adult, should be able to experience. The variety of sizes and colors, the individuality of each grain of sand, and the awareness that they are all of different origin and composition give an idea, in the small space that covers the microscope objective, of the enormous biological, chemical and geology of our planet.

And both the size, shape and composition of the sand grains are clues that specialists, called sandologists, a division of Geology, use to obtain the most diverse information about the environment of each sand sample and our planet. in general, acting as forensics that read a multitude of clues in each tiny specimen.

For example, sandologists at the Curtin School of Earth and Planetary Sciences have devised a way to determine the age distribution fingerprint of the mineral called zirconia in a sand sample, allowing us to better understand the evolution of the surface of our planet. planet over billions of years. The chemical elements contained in zirconia grains allow arenologists to date and reconstruct the conditions of the formation of that mineral, in a similar way, they explain, to that used by demographers to track the evolution of countries. The technique allows identifying the age population of zirconia grains in a sample since the one created at different geological times and in different places has a different composition. Thus, explains Dr. Chris Kirkland, of the group that developed the system, the sediments of the western and eastern coasts of South America are clearly identifiable. The western ones “were created from the earth’s crust that was subducted under the continent, causing earthquakes and volcanoes in the Andes” while, for their part, those on the Atlantic coast “everything is relatively calm from a geological point of view and “There is a mixture of old and young grains gathered from a great diversity of rocks in the Amazon basin.”

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But in addition to the study of its chemical characteristics, there is the physics aspect. First of all, there are the shapes: the more rounded a grain of sand is, it means that it has been subjected to greater erosion, which tells us not only about its age but also about the forces to which it has been subjected and the distance it has traveled since the point at which it separated from the bedrock. Furthermore, a small size favors greater mobility while a larger size keeps the sand closer to its origin, statistically.

Physics also studies the movement of sand for activities such as predicting the replenishment of beaches as their sand is displaced by water and wind. Likewise, the movement of dunes in the desert is a matter of capital importance since the movement of sand endangers the use of land for both agriculture and human habitation and transportation, covering roads and water channels. For this reason, satellite images are used to track the movement of the dunes in order to predict their future behavior and take preventive actions.

All of these scientific approaches give a new perspective to what we do with sand. Building a castle with it, as we have all done on the beach, thus becomes an exercise in playing with the geology and the deepest history of our planet.