All About Sand

Podcast Transcript

One of the most common substances on Earth is sand.

Most people don’t think very much about sand, but sand is an extremely important part of our world.

It isn’t just for building sand castles and going to the beach. Sand is the second most consumed resource in the world after water.

There is an entire science to sand, what different types consist of, how it is made, and even how it moves.

Learn more about sand and the surprising complexity of a seemingly simple subject on this episode of Everything Everywhere Daily.

Let’s start out with the basics and answer the question, what is sand? We all know sand when we see it, but how is it defined?

Sand isn’t a substance per se. There isn’t one type of sand. Sand is a term that covers a wide variety of sedimentary particles of a certain size.

To understand how sand is classified, it is important to understand the Wentworth Scale.

The Wentworth Scale and its modification, known as the Krumbein phi scale, is a widely used system for classifying sedimentary particles based on their size. It was developed by American geologist Chester K. Wentworth in 1922 as a modification of earlier systems to provide a standardized framework for describing grain sizes in sediments and sedimentary rocks.

The Wentworth Scale covers every sort of particle from the very large to the very small.

Anything with a diameter greater than 256 millimeters is considered to be a boulder.

Anything between 64 and 256 millimeters is called cobble. This would be the size of a river stone you might use for skipping rocks.

Anything from 2 to 64 millimeters is considered pebbles.

Finally, anything between 0.0625 and 2.0 millimeters is sand.

Below sand on the scale are silt and clay.

Sand can be further subdivided into very coarse, coarse, medium, fine, and very fine sand.

That is all that sand is. Any rock or mineral that has a diameter between 0.0625 and 2.0 millimeters is sand.

Sand and other sedimentary particles are created through a series of natural processes that break down larger rocks and minerals into smaller fragments. This process begins with weathering, the breaking down of rocks at or near the Earth’s surface.

Weathering occurs in three main forms: physical, chemical, and biological.

Physical weathering involves mechanical forces such as the expansion of water when it freezes in rock cracks, causing the rock to fracture or abrasion, where rocks grind against each other due to wind, water, or ice. Over time, these actions produce smaller and smaller particles.

Chemical weathering transforms rocks by altering their mineral composition through reactions with water, oxygen, or other chemicals. For instance, hydrolysis occurs when water reacts with minerals like feldspar, converting them into clay and soluble compounds. Similarly, oxidation causes iron-rich minerals to form rust-like substances, breaking down the rock.

Biological weathering, the third type, occurs when organisms such as plants and lichens physically break apart rocks or chemically alter them by secreting acids.

Once the rocks are broken down into smaller pieces, erosion removes these particles from their original location. Erosion is driven by forces such as water, wind, ice, and gravity.

Erosion is different from weathering in that it involves the movement of particles, whereas weathering does not.

For example, flowing rivers and streams carry sediments downstream, while wind transports fine particles like sand and silt across deserts. Glaciers, massive moving sheets of ice, scrape and grind the underlying rock, transporting the resulting particles far from their source.

Waves can also move and erode sand along shores and coastal areas.

The important thing to understand is that the process of weathering and erosion is going to be different for every collection of sand, depending on where in the world you find it.

While any rock or mineral of the right size can be considered sand, there are some types of sand that are very common all over the world.

The most common mineral that winds up as sand is quartz.

It is the most common mineral in sand due to its abundance in the Earth’s crust and resistance to weathering.

Quartz is a very hard mineral. It is a seven on the Mohs Hardness scale, which makes it much harder and more difficult to erode than most other minerals.

You will usually find quartz sand, where you find continental crust.

Quartz sands are frequently found on beaches, particularly in regions with extensive weathering of continental rocks like granite. The high energy of waves and currents often removes lighter or softer minerals, concentrating the durable quartz grains.

Most deserts contain a high amount of quartz. The Sahara Desert contains areas with significant quartz sand content, as does the Namib desert.

White sand beaches, like those in Siesta Key, Florida, or Whitehaven Beach in Queensland, Australia, are famous for their nearly pure quartz sand, also known as silica.

Fraser Island in Australia is known for some of the purest quartz sand dunes in the world.

However, not all white sand beaches are made out of quartz.

If you go to a tropical island, you may see a white sand beach. These beaches are almost never made out of quartz. They are made out of calcium carbonate, which is also white.

This type of sand primarily originates from biological processes and the breakdown of marine organisms. Coral, sea shells, and plankton exoskeletons are all made out of calcium carbonate.

When these organisms die, their shells and skeletons break apart due to wave action, predators, or decay. Over time, the fragments are ground into finer particles, forming sand.

There are also other types of white sand. White Sands National Park in New Mexico has sand made out of gypsum, which is also white. This type of sand is very rare and only found where you have exposed gypsum deposits.

Other types of rare sands can be found around the world as well.

Black sand can be found in places with active volcanism. This comes from the erosion of black volcanic basalt rock.

There are black sand beaches that can be found in Hawaii, the Canary Islands, Italy, Bali, French Polynesia, and other places around the world.

There are four places in the world where you can find green sand. The most famous of which is the Green Sand beach on the Big Island of Hawaii. There are also green sand beaches in Guam, Ecuador, and Norway.

The green sand comes from the mineral olivine. Olivine is very common in the Earth’s mantle but much rarer on the surface. It comes to the surface through volcanoes.

The green sand beach in Hawaii is the remains of a cinder cone with a high level of olivine. There is also an amber variant of olivine, which can be found with the green, but the green is what it is famous for.

On the island of Maui, there is a red sand beach that can be found not far from the town of Hana. The red is rust that comes from the iron-rich basalt found nearby. If the iron content were lower, the beach would be black instead of red.

Pink sand beaches are rare coastal areas where the sand has a distinct pink hue. The color comes primarily from tiny fragments of foraminifera, which are marine organisms with reddish-pink shells made of calcium carbonate.

These shell fragments mix with standard sand particles, often alongside crushed coral and other marine debris, creating the soft pink coloration. These beaches are typically found in tropical regions near coral reefs, such as the Bahamas and Bermuda.

As you are well aware, sand can form dunes.

Dunes have unique properties and are probably worth an episode of their own at some point.

Dunes are not static formations. They are always slowly moving as winds blow sand. They can sometimes move as much as several meters a year, and over centuries can change completely.

Singing sand dunes, also known as “booming dunes,” are a natural phenomenon where sand emits a deep, resonant hum or booming sound when it moves.

This occurs when large amounts of dry, well-sorted sand grains slide down the steep slopes of a dune under specific conditions. The sound is caused by the friction between sand grains, creating vibrations that resonate through the dune.

The pitch and tone of the sound depend on factors such as the size and shape of the grains, moisture content, and the speed of movement. Singing dunes are rare and can be found in deserts around the world, including the Sahara, Gobi, and Namib deserts.

As I mentioned in the introduction, sand is the world’s second most used natural resource, behind water. However, most of us don’t think of sand as a resource. Nonetheless, it is used for a wide variety of purposes.

High-purity silica sand is melted to create glass for windows, bottles, and screens. Likewise, Silica sand is used to manufacture optical fibers for telecommunications.

Ultra-pure quartz sand is refined to extract silicon, a critical material in semiconductors for electronics like computers and smartphones.

Sand is used in making tiles, pottery, and other ceramic products.

Foundries use sand molds to shape molten metal into precise forms.

Sand is also a natural filter used in water purification systems and aquifers.

The single largest use for sand, however, is in the construction industry.

Sand plays a critical role in construction as a primary ingredient in essential building materials such as concrete, mortar, and asphalt. In concrete, sand is combined with cement and gravel to create a durable, versatile material used in constructing buildings, bridges, roads, and dams.

Mortar, a mix of sand and cement, binds bricks, stones, and other materials in masonry. Sand also provides bulk and strength to construction materials, improving their structural stability. Additionally, it is used as a base material in road construction, as a filling material in land reclamation, and as a leveling agent beneath foundations and pavements.

However, there is a problem with the construction industry’s use of sand.

We are running out of it.

This might seem absurd at first because we have desserts full of sand. It is almost like saying we are running out of seawater.

Nonetheless, we are running out of sand because you can’t just use any old sand for construction, especially for creating concrete.

Desert sand is not suitable for construction because its grains are too smooth and rounded, a result of wind erosion that polishes the particles over time. These smooth grains lack the angular edges needed to create strong mechanical bonds with cement in concrete, leading to weaker structures.

Additionally, desert sand is often too fine and uniform in size, which prevents it from achieving the proper density and stability required for construction materials. In contrast, river or quarry sand has angular grains and a mix of particle sizes, making it ideal for creating durable and strong concrete and mortar.

The construction boom, particularly in fast-growing economies like India and China, has created immense demand for sand.

Most of the sand used for construction comes from sand mining, usually on beaches and riverbeds. However, easily accessible sources of the right type of sand are running out.

This has resulted in a surge in illegal sand mining, and it has become a big business for organized crime.

These criminal networks, often referred to as “sand mafias,” operate in countries like India, Kenya, and Cambodia, where they exploit poorly regulated or protected areas such as riverbeds, beaches, and coastal zones.

They extract sand in large quantities, bypassing environmental laws and not paying taxes. Their operations frequently involve violence, intimidation, and corruption, targeting activists, journalists, and officials who oppose them.

Sand can be found almost everywhere around the world, albeit in very different forms. It plays a vital role in everything from geology to biology to industry and even, it appears organized crime.