SAND, A GREAT NON-RENEWABLE SOURCE TO PROTECT

The effects of the storm, Vilanova i la Geltrú

Today, Claire Fontaine and The Grandma have gone to Vilanova i la Geltrú, a beautiful town near Barcelona, capital of Garraf county that suffered the consequences of a terrible storm some days ago.

Local storms are very usual in the Mediterranean coast during August. They are very intensive and they are sometimes very dangerous and aggressive. One of the first victims of these storms is the beach that often loses its sand as a consequence of these.

Sand is a primary element of our planet, but it is usually much unknown although it has an interesting history of creation and conservation.

Claire Fontaine and The Grandma have searched more information about sand at the same time they have enjoyed in Vilanova i la Geltrú with the great benefits of this amazing element.

After visiting Vilanova i la Geltrú, Claire and The Grandma have driven along the coast to Gavà to see the restauration works after the storm.

Before going to Vilanova i la Geltrú, The Grandma has studied a new lesson of her Ms. Excel course.

Chapter 12. Graphics (III) (Spanish Version)

Sand is a granular material composed of finely divided rock and mineral particles. It is defined by size, being finer than gravel and coarser than silt. Sand can also refer to a textural class of soil or soil type. A soil containing more than 85 percent sand-sized particles by mass.

The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica, silicon dioxide, or SiO2, usually in the form of quartz. The second most common type of sand is calcium carbonate, for example, aragonite, which has mostly been created, over the past half billion years, by various forms of life, like coral and shellfish. For example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean.

Sand is a non-renewable resource over human timescales, and sand suitable for making concrete is in high demand. Desert sand, although plentiful, is not suitable for concrete. 50 billion tons of beach sand and fossil sand is used each year for construction.

Sand, a great element of Nature

The exact definition of sand varies. The scientific Unified Soil Classification System used in engineering and geology corresponds to US Standard Sieves, and defines sand as particles with a diameter of between 0.074 and 4.75 millimeters. By another definition, in terms of particle size as used by geologists, sand particles range in diameter from 0.0625 mm or ​1⁄16 mm to 2 mm. An individual particle in this range size is termed a sand grain.

Sand grains are between gravel with particles ranging from 2 mm up to 64 mm by the latter system, and from 4.75 mm up to 75 mm in the former and silt particles smaller than 0.0625 mm down to 0.004 mm. The size specification between sand and gravel has remained constant for more than a century, but particle diameters as small as 0.02 mm were considered sand under the Albert Atterberg standard in use during the early 20th century.

The grains of sand in Archimedes' The Sand Reckoner written around 240 BCE, were 0.02 mm in diameter. A 1938 specification of the United States Department of Agriculture was 0.05 mm. A 1953 engineering standard published by the American Association of State Highway and Transportation Officials set the minimum sand size at 0.074 mm. Sand feels gritty when rubbed between the fingers. Silt, by comparison, feels like flour.

ISO 14688 grades sands as fine, medium, and coarse with ranges 0.063 mm to 0.2 mm to 0.63 mm to 2.0 mm. In the United States, sand is commonly divided into five sub-categories based on size: very fine sand (​1⁄16-​1⁄8 mm diameter), fine sand (​1⁄8 mm-​1⁄4 mm), medium sand (​1⁄4 mm-​1⁄2 mm), coarse sand (​1⁄2 mm-1 mm), and very coarse sand (1 mm-2 mm).

These sizes are based on the Krumbein phi scale, where size in Φ=-log2D; D being the particle size in mm. On this scale, for sand the value of Φ varies from −1 to +4, with the divisions between sub-categories at whole numbers.

More information: Nature

The most common constituent of sand, in inland continental settings and non-tropical coastal settings, is silica -silicon dioxide, or SiO2-, usually in the form of quartz, which, because of its chemical inertness and considerable hardness, is the most common mineral resistant to weathering.

The composition of mineral sand is highly variable, depending on the local rock sources and conditions. The bright white sands found in tropical and subtropical coastal settings are eroded limestone and may contain coral and shell fragments in addition to other organic or organically derived fragmental material, suggesting that sand formation depends on living organisms, too.

The gypsum sand dunes of the White Sands National Monument in New Mexico are famous for their bright, white color. Arkose is a sand or sandstone with considerable feldspar content, derived from weathering and erosion of a usually nearby granitic rock outcrop.

Sand, a great element of Nature

Some sands contain magnetite, chlorite, glauconite, or gypsum. Sands rich in magnetite are dark to black in color, as are sands derived from volcanic basalts and obsidian. Chlorite-glauconite bearing sands are typically green in color, as are sands derived from basaltic lava with a high olivine content.

Many sands, especially those found extensively in Southern Europe, have iron impurities within the quartz crystals of the sand, giving a deep yellow color. Sand deposits in some areas contain garnets and other resistant minerals, including some small gemstones. 

Rocks erode or weather over a long period of time, mainly by water and wind, and their sediments are transported downstream. These sediments continue to break apart into smaller pieces until they become fine grains of sand. The type of rock the sediment originated from and the intensity of the environment gives different compositions of sand.

The most common rock to form sand is granite, where the feldspar minerals dissolve faster than the quartz, causing the rock to break apart into small pieces. In high energy environments rocks break apart much faster than in more calm settings. For example, Granite rocks this means more Feldspar minerals in the sand because it wouldn't have had time to dissolve. The term for sand formed by weathering is epiclastic.

More information: Sand Atlas

Sand from rivers are collected either from the river itself or its flood plain and accounts for the majority of the sand used in the construction industry. Because of this, many small rivers have been depleted, causing environmental concern and economic losses to adjacent land. The rate of sand mining in such areas greatly outweighs the rate the sand can replenish, making it a non-renewable resource.

Sand dunes are a consequence of dry conditions or wind deposition. The Sahara Desert is very dry because of its geographic location and is known for its vast sand dunes. They exist here because very little vegetation is able to grow and there's not a lot of water. Over time, wind blows away all the fine particles, such as clay and dead organic matter, leaving only sand and larger rocks. Only 15% of the Sahara is sand dunes, while 70% is bare rock. The wind is responsible for creating these different environments and shaping the sand to be round and smooth. These properties make desert sand unusable for construction.

Beach sand is also formed by erosion. Over thousands of years, rocks are eroded near the shoreline from the constant motion of waves and the sediments build up. Weathering and river deposition also accelerate the process of creating a beach, along with marine animals interacting with rocks, such as eating the algae off of them. Once there is a sufficient amount of sand, the beach acts as a barrier to keep the land from eroding any further. This sand is ideal for construction as it is angular and of various sizes.

Marine sand or ocean sand comes from sediments transported into the ocean and the erosion of ocean rocks. The thickness of the sand layer varies, however it is common to have more sand closer to land. This type of sand is ideal for construction and is a very valuable commodity.

Europe is the main miners of marine sand, which greatly hurts ecosystems and local fisheries.

More information: Fraser Island Defenders Organisation

A beach is not only a sweep of sand,

but shells of sea creatures, the sea glass,

the seaweed, the incongruous objects washed up by the ocean.

Henry Grunwald