The Geology of Desert Sand

We use sand in virtually everything, from high-speed trains to our smartphones. But the world may be running out.

Sand consists of tiny particles of rock that have been eroded. All sand in desert regions originally came from somewhere else. In fact, many experts can tell exactly where that original location was by tracking footprints left behind in the sand.

Bedrock

Bedrock is a layer of rock that forms the upper surface of the rocky foundation that composes Earth’s crust. It can be igneous, metamorphic, or sedimentary in origin and is generally overlain by material such as soil and gravel. The thickness of bedrock varies from place to place, but it is usually at least a few feet thick. Bedrock can be exposed at the surface or hidden beneath a layer of less resistant materials such as sand and clay.

It is possible to mine bedrock in Minecraft, but it is not generally used as an item in the game. Instead, it is often incorporated into structures such as houses and towers. It is also sometimes used as the base for ruins.

In addition to providing a solid foundation for building and agriculture, the bedrock of the United States offers valuable information about the geologic history of the country. It can be found across the Nation and is the source of a rich diversity of natural resources, minerals, water, and landforms. In addition, access to the Nation’s bedrock geology is necessary for infrastructure development, natural resource management, mineral assessments, and other earth science research.

Geologists study the characteristics of the bedrock to determine its origin, tectonic setting, and geologic history. Geologic mapping is a vital part of this process, and the public often utilizes the results of the mapping in such activities as constructing roads and providing geologic information for water quality, mining, and energy resources.

In places where erosion is rapid, bedrock can be well-exposed. Such areas, called outcrops, are common in stream valleys and at the bases of hills and mountains. In deserts and mountain ranges that are above the treeline, bedrock exposure is even more common.

The type of weathering that occurs on the surface of bedrock depends on its composition and how it was formed. For example, a granite bed may be a target for mechanical weathering, such as glacial grinding and abrasion, while a limestone bed may be subject to chemical weathering. Both automatic and chemical weathering can cause fractures in the bedrock. Other methods of weathering include sheeting, where a large flat or curved area of the bedrock spalls off in layers, and spheroidal weathering, which produces rounded features.

Weathering

The processes that disintegrate rocks and form sand are called weathering. Usually, the process involves both chemical and physical weathering. Chemical weathering is more important overall, but it only works in humid and hot climates, while physical weathering is more prominent in cold and dry areas. The sand in deserts is typically derived from the mechanical weathering of bedrock. This is mainly because of the low moisture content in these environments.

Sand produced by mechanical weathering is typically rounded quartz grains. This sand is often used for non-structural construction projects such as landscaping, filling, and paving. Its unique color and texture can also add a distinct beauty to many environments.

However, the high concentration of silica found in desert sand can present some problems when it is used for structural construction. This is because it does not offer the necessary number of “bonding bridges” that help give concrete its strength. The high silica content of desert sand can also cause the concrete to become weak, brittle, and crumbly.

In addition to sand, desert sand contains a variety of other minerals and particles. Some of these are crystalline, such as mica and quartz, while others are part of the mineral group known as feldspars. This sand may also contain traces of other materials, such as iron and magnesium.

One of the most unique features of desert sand is its dark surface coating, known as desert varnish. This is a thin, dark brown surface coating of clays and iron and manganese oxides. It is a product of both biological and cosmogenic weathering.

Another exciting aspect of desert sand is that it tends to form ripples and dunes. Ripples are low ridges that can be straight or wavy, while dunes are more significant hills. As the winds blow the sand, they create these structures. When it rains, water seeps into the sand and moves it around. Often, this movement causes temporary rivers and streams to form.

One other common feature of desert sand is that it is scorched. This means that items buried in it will not rust as quickly as they would in wetter environments. It is a myth that metal must be soaked to rust, though; it simply needs oxygen and a hard, rough surface.

Erosion

Erosion is the natural process of loosening and breaking apart rock and soil from Earth’s surface. Erosion can be caused by weathering, the natural aging of stones and other materials, or by the movement of water or wind. In desert areas, erosion is a significant factor in the formation of dunes. The winds are constantly pushing sand, and over time, it builds up to form giant dunes or even whole sand seas.

When a dune is formed, the sand becomes bonded together by a network of “bonding bridges.” If the bridges are dry, they provide considerable bearing strength and resist erosion. However, if the sand is wet, the bridges lose their power and break, allowing the sand to fall away.

In the desert, erosion is further aided by weather patterns and topographical features. The constant winds in the region blow dust over large areas, creating an ever-shifting landscape. The sun also is an integral part of erosion, as it heats rocks and causes them to expand. The expanding stones can crack and crumble, or they may become sand-sized pieces that are carried by the wind.

The sand in the desert is lovely and smooth, which makes it less suitable for construction projects than beach or river sand. This is because the sand grains do not interlock as well. It can lead to structural problems if used in concrete and other building materials. Fortunately, there are methods of treating the desert sand to make it more suitable for use in construction.

Researchers have found that if the sand is treated with a 1:1 cementation solution and allowed to cure for five days, it will be much more resistant to erosion than untreated sand. Wind tunnel tests with varying wind speeds confirmed this. The results showed that the biotreated sand samples were able to resist decay significantly better than untreated sand at wind speeds of 10 and 30 m/s. In addition, the calcite content percentage, crust layer thickness, and bulk density of the biotreated sand increased with increasing treatment duration.

Deposition

In geology, deposition is the laying down of sediment carried by wind, flowing water, the sea, or ice. The residue may be pebbles, sand mud, or salts deposited by organic activity or evaporation of seawater. Deposition can form features such as alluvial fans, desert dunes, or sand sheets.

Sand is a distinctive feature of deserts, as well as the coasts of oceans and lakes. It is a mixture of rock fragments, such as quartz, feldspar, and mica, and is often reddish brown due to high concentrations of iron oxide, known as rust.

The sand particles are shaped by the forces of erosion and weathering and by the type of rocks from which they are composed. They may be angular, as in sand from granitic rocks that glaciers have eroded, or they may be rounded, as in sand from volcanic lava flows. The rounding process, known as pitting, gives sand grains a characteristic pattern of abrasion marks called textural signatures. These provide clues to their past and can also reveal how a dune was formed or moved over time.

Sand grains can be transported long distances by wind, and the process of migration and accumulation forms dunes. The sand is compacted as it accumulates and may form ripples or steep slopes that are referred to as the angle of repose. Erosion on one side of the dune and deposition on the other results in a gradual build-up of sand.

Desert sand can be used for construction, although it is not as good as beach or river sand. The reason is that desert sand has less interlocking between the grains, and this makes it difficult for it to bond together. This can cause problems with concrete and mortar that is built using desert sand.

In addition, sand from deserts can be exported in enormous quantities, traveling to other areas around the world where it is used in construction and fertilizing crops. It is estimated that the Amazon forest would not exist without the fertilization supplied by Sahara dust.