Sand facts for kids
glass, dune, quartz,
volcanic, biogenic coral, pink coral,
volcanic, garnet, olivine.
Samples are from the Gobi Desert, Estonia, Hawaii and the mainland United States. (1×1 cm each)
Sand is a loose, granular material found all all over Earth. It is made of tiny bits of minerals and broken rocks. Sand is everywhere, from ocean shores to wide deserts. You can find it on a sunny beach, along rivers, and in play sandboxes.
To a geologist, sand is defined mainly by the size of its grains. Sand grains are smaller than rough gravel. They are also coarser and larger than powdery silt. When you rub sand between your fingers, it feels gritty. Silt, on the other hand, feels very smooth, just like kitchen flour.
Sand is also used to describe a special textural class in gardening. Soils that have more than 85 percent sand grains are called sandy soils. Sand is essential for life, science, industry, and building things like cities.
Contents
What Is Sand Made Of? Composition and Minerals
The exact minerals in sand depend heavily on the local rocks and the environment. Different places on our planet have completely different types of sand grains.
Common Minerals and Quartz
The most common ingredient in sand is silica, also known as silicon dioxide (SiO2). It usually appears as the mineral quartz. Quartz is extremely hard and chemically tough. Because quartz does not dissolve easily, it survives severe weathering much better than softer rocks.
On inland continental lands and non-tropical shores, quartz is the top mineral found. Often, sands have tiny traces of iron trapped within the quartz crystal shapes. This iron rust gives the sand a deep golden or yellow shade. You can see these warm yellow sands in many parts of Southern Europe.
Colorful Sands and Special Minerals
Not all sand is yellow, beige, or golden. Sand comes in almost every color of the rainbow depending on local minerals. For example, rocks from a volcanic basalt flow create dramatic black sands. Black sands are also created by dark shiny minerals like magnetite or volcanic obsidian.
Green sand gets its unusual olive color from minerals like olivine, chlorite, and glauconite. These green crystals wash out of cooled basaltic lava. Other sands contain tough red garnet minerals and tiny bits of precious gemstone stones.
Some rocks break down into sandstone rich in feldspar, creating a mix called arkose. Arkose sand comes directly from the erosion of exposed granitic rock outcrops. In Utah, at the famous Coral Pink Sand Dunes State Park, the quartz grains are coated with hematite. This iron coating turns the entire landscape a glowing coral orange color.
Sands from Living Creatures
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Sand can also form directly from living things like plants and animals. We call this biogenic sand. Calcium carbonate is the second most common substance found in world sands. One major form of calcium carbonate is a crystal called aragonite.
Over hundreds of millions of years, marine life forms create vast amounts of aragonite. Sea animals such as coral and hard-shelled shellfish make protective shells out of this mineral. When these animals die, ocean waves crush their shells into tiny white fragments.
Tropical places like the Caribbean have dazzling white sands made of crushed reefs. These sands show that sandy beaches can depend entirely on healthy living organisms. Over long periods, ocean limestone also erodes, adding more bright white bits to the coast.
Gypsum Dunes and Rare Minerals
Some sands are made of rare, water-soluble crystals of calcium sulfate. The most famous mineral of this type is soft white gypsum, along with its clear form called selenite. Because gypsum dissolves quickly in rain, it rarely stays intact long enough to form sand.
However, gypsum can build great sand plains in very dry, enclosed desert valleys. A stunning example exists at White Sands National Park in sunny New Mexico. Another protected place is the famous Salt Plains National Wildlife Refuge in the United States. In these dry basins, sparkling white gypsum dunes drift across the desert landscape.
How Is Sand Formed? The Power of Weathering
Sand takes thousands or even millions of years to form through patient natural forces. Large mountain boulders slowly break apart through natural processes known as weathering and erosion.
Water, Wind, and Erosion
Rain, moving ice, and blowing wind slowly grind huge cliffs down into rough sediments. Flowing mountain streams push these rough gravels downstream. As the rocks bang into each other, they smash into smaller fragments. Geologists use the word epiclastic to describe sand grains made through this natural rock breakdown.
The original rock determines what the new sand contains. For example, granite contains hard quartz along with softer feldspar minerals. As water flows, the softer feldspar breaks down faster, leaving behind the tough quartz grains. In fast, raging rivers, stones crash together violently and shatter quickly before feldspars can dissolve.
The Journey to the Ocean
Eventually, broken sediments reach rivers, shores, and ocean bays. Sand from rivers often settles quietly onto a wide, flat flood plain. Over thousands of years, crashing ocean waves grind coastal stones into smoother beach sand.
Marine creatures also help build sand when they scrape algae off stones with their mouths. Once sand builds up along a coastline, it forms a natural barrier. This natural barrier shields inland dirt from being eaten away by wild ocean waves.
Sand Grain Sizes and Scientific Scales
Scientists use exact rules to define what counts as a grain of sand. They study particles carefully using laboratory sieves, microscopes, and mathematical sizing charts.
Sizing Systems for Earth Scientists
The engineering world often relies on the standard Unified Soil Classification System. Under this system, sand particles measure between 0.074 millimeters and 4.75 millimeters wide. By comparison, pebbles larger than 4.75 millimeters up to 75 millimeters are considered gravel.
Another popular geological scale defines sand as measuring from 0.0625 millimeters up to 2 millimeters wide. Particles smaller than 0.0625 millimeters down to 0.004 millimeters are classified as smooth silt. Anything smaller than that becomes fine sticky mud or clay.
Historical Sand Definitions
Long ago, the ancient Greek thinker Archimedes studied sand in his book The Sand Reckoner. Written around 240 BCE, he imagined filling the entire universe with tiny sand grains! He used sand sizes around 0.02 millimeters wide in his calculations.
In the early twentieth century, an expert named Albert Atterberg also used 0.02 millimeters for sand. In 1938, the United States Department of Agriculture set their minimum sand line at 0.05 millimeters. Later, in 1953, the American Association of State Highway and Transportation Officials established 0.074 millimeters as the minimum size.
Modern Sizing Standards
Global groups like the International Organization for Standardization (ISO) use ISO 14688 to grade sand into clear categories:
- Fine sand: grains measuring from 0.063 millimeters up to 0.2 millimeters across
- Medium sand: grains measuring from 0.2 millimeters up to 0.63 millimeters across
- Coarse sand: grains measuring from 0.63 millimeters up to 2.0 millimeters across
American geologists often break sand into five sizes using the logarithmic Krumbein phi scale. On this mathematical scale, Greek letter phi (Φ) ranges from −1 to +4 for sand. The five official American groupings are very fine, fine, medium, coarse, and very coarse sand.
What Sand Grains Look Like: Shape and History
If you look closely at sand grains under a microscope, you can read their history. Sand grains tell exciting stories about where they came from and how far they traveled.
Sharp Sand and Grus
When rock breaks down near its original home, the new grains keep jagged edges. Freshly broken quartz from gneiss or granite looks rough and sharp. Geologists call these fresh, crumbly rock bits grus.
In the construction trade, builders call this material sharp sand. Gardeners love sharp sand because its rough edges keep clay soil loose and airy. Because the grains have sharp edges, they lock together tightly when mixed into wet cement.
Rounded Desert Sand
When sand travels long distances, natural forces tumble and rub the grains together. Water currents and wild desert winds knock off every sharp corner, leaving the grains round.
In the gigantic Sahara Desert, strong winds blow loose sediments across great distances. The Sahara is very dry because of its geographic spot near Earth's warm equator. Constant dry winds blow away tiny dust and dried leaves, leaving rounded sand grains behind.
Although the Sahara is famous for towering dunes, only 15% of it is sand dunes. The other 70% of the Sahara landscape is made of hard, bare rock! Wind storms leave distinct frost marks and microscopic pits across these rolling desert grains.
Studying and Collecting Sand
Scientists examine sand grains using advanced tools like the scanning electron microscope. People who collect sand samples from world beaches as a hobby are called arenophiles.
Some organisms love living buried deep inside sand dunes and ocean beaches. Scientists call these sand-dwelling creatures psammophiles. For example, the tiny sand rat thrives comfortably in dry, sandy desert habitats.
How People Use Sand in Daily Life
Sand is one of the most useful natural substances on our planet. Humans use billions of tons of sand every year for hundreds of important jobs.
Building and Construction
Sand is a main ingredient in the building materials that create our modern world:
- Concrete: Sand mixes with cement, gravel, and water to make strong concrete for bridges and buildings.
- Mortar: Masons blend fine sand with Portland cement and lime to glue bricks together tightly.
- Brick: Factory workers mix sand directly with moist clay before firing strong building bricks.
- Cob: An old building mixture made of clay, straw, water, and sand, where coarse sand forms up to 75% of the mix.
- Sand casting: Foundries use special heat-safe molding sand to cast molten metals into complex machine shapes.
Industry, Technology, and Glass
Because sand is full of pure quartz, it is critical for high-tech industries:
- Glass: Workers melt high-purity silica sand at extreme temperatures to make windows, jars, and mirrors.
- Silicon: High-grade quartz sand is melted to extract pure elemental silicon for computer chips and solar cells.
- Abrasion: Builders use fine sand grains for smooth sandblasting to clean metal machinery and polish stone.
- Paint: Stirring sand into paint creates a non-slip rough textured finish on stairs and floors.
- Hydraulic fracturing: Energy workers use round silica grains as a durable "proppant" to hold open underground cracks.
Filtering, Farming, and Safety
Sand acts as a natural cleaner and safety shield in many situations:
- Water filtration: Cities clean drinking water by running it through deep rapid sand filters.
- Air filtration: Early emergency gas mask filters used sand, though modern masks use microfiber materials today.
- Agriculture: Sandy soil drains extra water quickly, making it great for crops like peanuts and watermelons.
- Sandbags: Workers stack heavy bags filled with sand to block raging floodwaters and shield fragile walls.
- Road safety: Highway trucks spread sand on slippery winter roads to give car tires extra grip.
- Train rails: Locomotive engine drivers and rail transit operators drop sand on rails to stop slipping on steep tracks.
Fun, Art, and Culture
Sand brings joy, creativity, and spiritual meaning to people around the world:
- Sandcastles: Building a sculpted sand castle on the ocean shore is a favorite childhood pastime.
- Sandboxes: Neighborhood parks install wooden frames filled with clean sand for younger kids to dig safely.
- Dune sports: Outdoor enthusiasts love riding open beach buggy cars across sweeping dunes.
- Sand animation: Talented Performance artists spread sand over lit glass tables to draw moving picture stories.
- Aquariums: Fish hobbyists spread clean sand across home tanks, especially when keeping sensitive marine reef tanks.
- Ancient defense: In ancient times, defenders used heated sand as an unusual thermal weapon dumped from high castle walls.
- Religious traditions: In Islam, believers perform Tayammum, a ritual spiritual cleansing using clean sand when water cannot be found.
- Nature's builders: Marine animals called zoanthids lack normal bones, so they glue sand into their soft mesoglea body layer for strength.
Protecting Our Sand: Environmental Issues
Sand might seem endless, but the right kind of sand is actually a non-renewable resource. Desert sand grains are too round and smooth to lock together inside strong concrete. Builders must rely on angular sand from running rivers, lakes, and ocean beaches.
Sand Shortages and River Damage
Humans use over 50 billion tons of sand and gravel every single year. The world building industry spends billions of dollars buying sand for growing cities. Because humans take sand faster than rocks can weather, natural river beds are running out of sand.
To collect underwater sand, companies use a noisy floating machine process called dredging. Massive floating pumps suck sand up from river bottoms into giant cargo barges. This dredging tears up plant life, destroys local fisheries, and ruins freshwater river habitats. Stripping sand away from riverbanks causes landslides that destroy farmland, bridges, and homes.
Ocean Reefs and Vanishing Beaches
Taking sand from ocean floors harms fragile marine life and ruins underwater ecosystems for decades. Governments sometimes try to rebuild damaged shorelines through a process called beach nourishment. Workers pump ocean sand back onto disappearing tourist beaches, but storms often wash it right back out.
Some places have run out of sand completely. The city of Dubai in the United Arab Emirates built gigantic artificial islands known as the Dubai Islands. These giant palm-shaped island projects used over 835 million tonnes of sand! Dubai used up its own sea floor sand, so it had to buy ocean sand from Australia.
Because sand mining causes severe harm, nations like China, Malaysia, and Cambodia have banned sand exports. In 2012, director Denis Delestrac created an eye-opening documentary film named Sand Wars. His film showed how the demand for sand causes habitat loss and fuels problems with the illegal sand trade.
In 2022, the United Nations Environment Programme called on all countries to protect beaches. Experts want humans to recycle building materials and adopt a sustainable circular economy. Builders can also crush quarry stone into artificial grains called manufactured sand to replace fragile river beds.
Staying Safe Around Sand
While sand is fun to play with, it can cause safety issues if people are careless. Fine silica dust from industrial sandblasting can damage human lungs. Today, workers follow strict rules on the Safety data sheet and wear protective air masks.
At the beach, children should never dig deep holes in dry sand. If sand walls collapse, heavy sand can trap a person underneath in seconds.
Another natural hazard is quicksand, which forms where underground water bubbles up through loose sand grains. Quicksand is a strange water-rich colloid hydrogel mixture that acts like a thick liquid. While quicksand cannot pull you completely underwater, getting stuck can leave you stranded when ocean tides roll in.
Images for kids
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Sand dunes in the Idehan Ubari, Libya
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Depiction of sands from different places around the world
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Heavy minerals in a quartz beach sand from Chennai, India
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Sand from Coral Pink Sand Dunes State Park, Utah
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Sand from Pismo Beach, California
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Close up of black volcanic sand from Perissa, Santorini, Greece
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Scanning electron micrograph showing grains of sand
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Pitted sand grains from the Western Desert, Egypt
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Sand grains of yellow building sand under a microscope
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Road with sand warning sign
Related Pages
In Spanish: Arena para niños
- Aggregate (geology)
- Beach
- Construction aggregate
- Coral Pink Sand Dunes State Park
- Desert sand (color)
- Dry quicksand
- Energetically modified cement
- Heavy mineral sands ore deposits
- Oil sands
- Papakolea Beach
- Particle size
- Punaluʻu Beach
- Quicksand
- Red Sand Beach
- Revolving rivers
- Sand art and play
- Sand Beach (disambiguation)
- Sand equivalent test
- Sand island
- Sand mining
- Sand rat
- Sandstone
- Sandstorm
- Sand theft
- Singing sand
- White Sands National Park
