Contrary to Anikin Skywalker’s famous Star Wars quote, certain types of sand aren’t coarse, rough, or everywhere. We’re all familiar enough with beach or Saharan dune sand, at least from a pedestrian perspective. Still, there’s a lot more variety than you might expect.
The many types of sand include:
- Silica Sand: A Glassmaker And Tourist Attraction
- Beach Sand: The Coastal Compliment
- Immature Sand: A More Complex Personality
- Heavy Mineral Sand: An Asset To National Security
- Biogenic Sand: Weathered Skeletons
- Manufactured Sand: The Answer To The Shortage
- River Sand: The Old Faithful
- Ooid Sand: The One That Grows
- Dune Sand: The Product Of Wind
- Green Sands: Temporary And Periodic
- Volcanic Sand: The Black Sand
- Pit Sand: Free From The Ills Of Exposure
- Mason Sand: Also Known As Builders’ Sand
Table of Contents
1. Silica Sand: A Glassmaker And Tourist Attraction
Silica sand generally consists of an extremely high percentage of fine, rounded quartz grains. It’s industrially sought out, as it’s the source material for glass manufacture.
When the grain size is strictly controlled, and purity is high, it is often referred to as industrial sand.
Mature silica sand is white, giving the famous Floridian beach of Siesta Key its characteristic brightness. However, not all white sands are concentrated with silica: New Mexico’s White Sands National Monument features dunes of gypsum instead.
Silica refers to silicon dioxide, of which pure quartz is made. But not all silica is quartz. For example, opals are a type of silica. The key to quartz’s prevalence is its exceptional stability and weathering resistance. This allows it to naturally concentrate as other minerals erode.
2. Beach Sand: The Coastal Compliment
Beach sand is found in coastal areas worldwide, ranging from bright white to yellow-brown to muddy grey. It is mainly comprised of quartz, feldspar, and mica. In addition, beach sand typically contains other impurities, such as biogenic sand.
Beach sand is often readily available for consumer purchase, especially for:
- Sandpits,
- Golf course bunkers
- Jointing for paving and slabs
However, beach sand is avoided for construction and industry due to the following:
- Too impure for manufacturing
- Contains chlorides, which can contribute to the corrosion of metal construction beams
- Absorbs atmospheric or ground moisture, mainly due to its salt content
3. Immature Sand: A Developing Personality
Immature sand is larger and chunkier grains that still resemble its source rock. Rocks are conglomerations of minerals, but the less chemically and physically erosion-resistant minerals are lost as they weather away.
Quartz is among the most common, stable minerals and is thus often a majority fraction of mature sands. But immature sand has many other mineral components which will dissolve as the grains weather.
The most extreme form of immature sand is called ‘lithic.’ Lithic sand is primarily comprised of fragments of the source rock, is usually not far from the source, and has been subjected to less erosion.
4. Heavy Mineral Sand: An Asset To National Security
As the name suggests, heavy mineral sand (HMS) is relatively rich in dense minerals. The grains that classify HMS are at least 2.9 times as heavy as an equivalent volume of water. For comparison, quartz has a relative density of about 2.65 times.
HMS is sometimes commercially mined for its constituent metals, such as titanium, aluminum, zirconium, and rare earth elements. These elements have applications across consumer, industrial, and defense sectors.
Some minerals that can be found in heavy mineral sands include:
- Titanium-containing: ilmenite, leucoxene, and rutile
- Zirconium-containing: zircon
- Iron-containing: magnetite
- Rare earth element-containing: monazite
The US government has made a concerted effort to assess its available HMS resources to fortify its supply chains, especially for its defense sector.
5. Biogenic Sand: Weathered Skeletons
Sometimes loosely called “coral sand,” biogenic sand originates from the exoskeletons or bones of deceased creatures – typically marine. Pure biogenic sand is mostly calciferous, although some also contain silicates. Biogenic sands tend to have plenty of impurities.
The grains are highly irregular and frequently intricate. The color is usually white or beige, but containing pink grains is also common.
Key sources include:
– Molluscs
– Sponges
– Corals
– Sea urchins
– Foraminifera
– Algae
6. Manufactured Sand: The Answer To The Shortage
Manufactured sand (also known as M sand, artificial sand, and crushed-rock sand) is the product of blasting, grinding, crushing, and sieving rocks such as granite or basalt into fine sands of specified grain sizes. The particular rocks used often give manufactured sand a greyish color.
Artificial sand is not synthetic or lab-made. While “crushed rock” is a rarer descriptor, it’s less misleading. However, the resulting grains are distinct from their natural counterparts: they’re often made to be finer, denser, and less contaminated.
The need for manufactured sand is becoming more prevalent. Sand is a non-renewable resource on human timescales, and the world is running out of accessible quantities of high-quality sand for uses such as chip wafer manufacturing and construction.
Further, dredging sand is a considerable civil risk near shores due to landslides. Dredging is also often ecologically devastating, as the sea floor is left destroyed, and recovery takes a long time.
7. River Sand: The Old Faithful
River sand, also known as natural sand, is a catch-all term for various naturally formed sand extracted from the earth. When removed from river beds and shores, river sand has a large fraction of impurities, and the grains tend to be exceptionally smooth.
River sand is the primary choice for mixing concrete and construction. The sand is also available for purchase from hardware stores for DIY projects.
However, it is limited in quantity, accessibility, and suitability. The silt layer on top and gravel layers below, where tiny are present, must often be filtered out too. Its extraction almost always has a substantially adverse impact on the surrounding environment.
8. Ooid Sand: The One That Grows
Ooid sand is composed of small, spheroid/oblong grains. They are most commonly marine, forming in warmer, wave-agitated water. They have the characteristic look of a miniature, off-white, pebble beach.
Ooids are accretionary, unlike typical sand grains, which weather down over time. Ooids form as minerals such as calcite and aragonite deposit onto small particles, acting as nuclei. Ooids’ even shape results from the agitation and deposition, with the warm water reducing dissolved carbon dioxide.
Due to their accretionary nature, ooids exhibit concentric rings akin to trees’ growth rings. They also tend to resemble the shape of their crystallization nucleus.
Formation of ooid sand famously occurs in:
- The Persian Gulf
- The Gulf of Mexico near the Yucatán Peninsula
- The Bahama platform
A well-known, non-marine example is the Great Salt Lake in Utah.
9. Dune Sand: The Product Of Wind
Desert sands vary greatly, but the especially wind-stripped sands of giant dunes are typically:
- Very consistent in size (i.e., “well-sorted” by desert winds)
- Mostly free from dust (dust is much smaller and more varied in composition)
- Predominantly well-rounded quartz grains, but impurities are common
Saharan sand dunes are mostly made up of quartz. On the other hand, the sand dunes of the Dubai Desert tend to have a lot of biogenic impurities – it’s close to the ocean, after all.
While it may seem that Saharan dunes are a ripe source for industrial manufacturers’ demand for sand, they’re unfortunately unsuitable due to their shape, variability, impurities, etc. Of course, that’s not to speak of the difficulty of transport.
10. Green Sands: Temporary And Periodic
While not a familiar sight for most of us, sands with green colors or pigmented constituents are numerous. Rarer finds include malachite, serpentine, and epidote, but you have a better chance of encountering the following two.
Olivine Sand
Olivine sand is famously green, giving the Hawaiian Papakolea/Green Sand Beach its unique tinge (and others). As a magnesium iron silicate, it’s remarkably dense, allowing waves to separate it out into deposits, such as onto beaches.
Olivine is a plentiful constituent of some igneous rocks. On the other hand, it is unstable in its granular form and is particularly prone to breaking down. Thus, it’s mainly found in volcanic regions. In fact, it’s amongst the least stable minerals and is totally unsuitable for construction.
Greensand
Greensand is both a kind of sand and sandstone, containing glauconite in particular. The sand grains are typically small, round, and dark green.
Greensand sandstone formations are usually coastal or marine. They are thought to have formed in the Cambrian and Cretaceous periods for the most part.
11. Volcanic Sand: The Black Sand
While not always black, a subset of volcanic sands is most well known as “black sand” and is famous for complimenting the coasts of places such as Ireland and Hawaii.
The color is a result of their richness in the following:
– Magnetite, a heavy, iron-containing component that aligns with strong magnetic fields
– Obsidian, effectively volcanic glass
– Augite/pyroxene
Olivine and basalt are also relatively common components of volcanic sand due to the igneous nature of the source.
Volcanic sand’s constitution and properties vary wildly. Sometimes it’s mostly mineral ash directly from an eruption. Other times, it’s the admixture of weathering igneous rocks with other sediments.
The color aside, it’s not particularly special: avoid paying extra for volcanic sand massages. Quartz is usually abrasive enough to slough off dead skin cells, and unlike plants, you cannot absorb minerals through your skin.
12. Pit Sand: Free From The Ills Of Exposure
Digging a few meters down will often yield “pit sand” in various geologies. Pit sand is characterized by its sharp, angular, and coarse nature. These large grains bind well due to their shape and thus are commonly used for concrete.
The majority of pit sand is tinged red-brown. This is caused by the presence of pigmenting iron oxides.
The mining of pit sand for construction is done away from coasts to avoid additional salts. These salts would otherwise promote steel corrosion, absorb excessive moisture, and cause efflorescence. Low silt content is also required for construction concrete.
13. Mason Sand: Also Known As Builders’ Sand
Mason sand is classified by its fine texture and consistent grain size. In addition, it’s often specified to be highly pure.
Made of smaller grains, this sand is most used for making mortar and finer concretes that give an aesthetically preferable finish between brickwork and patio tiling. Don’t mistake it for not being general purpose, though. It’s an ideal choice for everything from landscaping to apartment blocks.
