What are the properties of sea sand




  sand is a naturally occurring, unconsolidated sedimentary rock with a grain size of 0.063–2 mm.

Emergence

Sand is created by the physical and chemical weathering of other rocks. The original starting material are igneous and metamorphic rocks (e.g. granite), from which the crystals of the mineral components are typically extracted.

The grains are transported by gravity, wind and water and are mixed and sorted. Since the surface, which is exposed to weathering and wear and tear during transport, is greatly enlarged, its forces can now better apply, so that the mineral composition of the sand and the shape of the grains change comparatively quickly. Larger grains are turned into smaller ones by splitting them along the crystal interfaces or by breaking out smaller grains when the grains collide with one another. Some minerals (especially mafic minerals) are quickly chemically converted and broken down under the influence of the weather, so that their share in the total amount of sand decreases significantly.

The shape of the individual grains changes due to mechanical influences during transport; In general, corners and edges are rounded and sanded down the longer the transport route. However, this is not a linear process: the rounder and smaller the grains, the more resistant they are to further changes. Investigations have shown that a transport route of thousands of kilometers is often necessary in order to even moderately round grains of sand of medium size.

When transporting along rivers, these distances can rarely be reached, and the constant movements in the surf zone of a beach are in most cases insufficient to explain the roundness of grains of sand, especially if the sand consists mainly of resistant quartz. The vast majority of the sand that occurs on earth therefore comes from sandstones and has already had several erosion cycles behind it: Sand is deposited (sedimented), covered by other sediments, solidified, and the grains are cemented together by binding agents (diagenesis). When the rocks are exposed to erosion again after a tectonic uplift, the individual grains are exposed and rounded a little further during the following transport, and another cycle follows. Even if one assumes a cycle duration of 200 million years, a well-rounded grain of quartz sand today can have gone through ten erosion cycles and thus almost half the history of the earth.

A special case is sand that was formed from the remains of dead living beings, e.g. B. mussels or corals. Viewed in geological terms, this sand is very short-lived, as the individual grains are normally so strongly changed during diagenesis that they can no longer appear in their original form after renewed uplift and erosion.

composition

The mineral composition of sand can vary greatly depending on the location. The majority of the sand deposits, however, consist of quartz (silicon dioxide SiO2), because it is not only frequent, but also particularly resistant to weathering due to its hardness (7 on the 10-point Mohs hardness scale) and its chemical resistance.

However, other types of sand are also possible. For example, the fine, white sand on the beach of coral islands consists of ground coral skeletons, and thus mainly of calcium carbonate (CaCO3). The green sand from the beaches of Hawaii, which gets its color from the volcanic olivine, is also known. Fine-grained, weathered basalt provides black sand, which consists primarily of mafic minerals. Depending on the composition of the sand, a distinction is made, for example:

  • Shell sandconsisting of more or less rounded particles of mollusc shells,
  • Coral sand, which consists of the calcareous remnants of corals and is found everywhere on coral islands
  • Volcanic sandthat either originated from lava that was eroded by the force of flowing water or the impact of waves on the banks of larger bodies of water or that formed in the form of volcanic ash directly during volcanic eruptions.

Classification and designations

In soil science, the sandy soil is the coarsest of the four main types of soil. According to the preferred classification in German-speaking countries according to DIN 4022 (1955), a distinction is made between the following grain size ranges:

Sand (S) Grain size
Coarse sand (GS) 0.63 - 2.0 mm
Medium sand (mS) 0.20-0.63 mm
Fine sand (fS) 0.063-0.20 mm

Grain classification based on the equivalent diameter

In practice, however, there are also slightly different class boundaries. Coarse silt and sand are classified according to the classification by Engelhardt (1953) hereinafter referred to as Psammite.

Coarser sand is called “Grand” in northern Germany, a name that is also used in the classification by Engelhardt is used for a grain size range that includes most of the coarse sand and fine gravel class of the DIN standard. Sands, which consist mainly of grains of one grain size, are called "well sorted"; accordingly, "poorly sorted" sands are those in which a wide range of grain sizes is represented. Flying sand is the name given to sand that is particularly easy to move by the wind due to its purity, small grain size and good sorting. If it occurs over a large area, it often appears in the form of dunes.

Low-cohesion sands can be "liquefied" with a small amount of water and are then known as quicksand.

Squeeze sand is artificially produced sand with broken, sharp-edged grains.

distribution

Sand occurs in more or less large concentrations all over the earth's surface. However, there are significant differences in the distribution, which depend on factors such as parent rock, climate, geological history and transport medium. In the high mountains, sand is only found sporadically, apart from the moraines of valley glaciers and the deposits of rivers. In the low mountain ranges and in the lowlands, however, sand is often transported and sedimented by meandering rivers. There are sometimes huge sand deposits at the bottom of lakes. The sand can be blown out of sandbanks and floodplains and transported over long stretches (aeolian transport), just as the lack of a closed vegetation cover favors the attack of the wind. For many people, the term "desert" is associated with the image of dunes, and in fact large parts of the Sahara and the Namib as well as the West Asian deserts are characterized by sand as so-called sand deserts (although it does not always appear in the form of dunes) . In the cold climate zones, there are large expanses of sand in the vicinity of foreland glaciers and inland ice, which are known as sanders. The melt waters of the inland ice sheets of the last ice ages are responsible for the abundance of sand in northern Germany and especially in Brandenburg. There are also significant sand deposits where rivers flow into the sea to form a delta. The sand is then further distributed by currents parallel to the coast and appears as a beach and sandbank. Eventually, large amounts of sand are deposited on the continental shelves, from where parts of it are carried into the deep sea plains by suspension currents.

In general, it can also be said that there are particularly large deposits of sand where sandstone is on the surface and thus serves as a starting material. In areas with extensive limestone cover, on the other hand, chemical weathering predominates: the rock is loosened and shows the typical treasure trove of karst; Lime sand only has a short service life under these conditions due to its large surface area. This explains, for example, the extensive absence of sandy beaches on the Croatian coast, because both the coast itself and large areas of the interior are exclusively characterized by limestone (Dinaric Karst). Furthermore, chemical weathering also plays an important role in the continental, always humid tropics, and for this reason, larger deposits of sand are rather rare here as well.

Erosion by sand

Sand moved by the wind and other fine-grained sediments can cause corrosion (wind grinding, wind erosion) on rock formations according to the principle of the sandblasting fan and develop characteristic, sometimes bizarre forms of erosion, for example wind edges, mushroom rocks or yardangs.

Sand as a habitat

Sandy landscapes are not synonymous with dead and bare landscapes, such as B. the "classic" desert. Thrive in the sand, among other things. the beach grass (Ammophila Host.), The sand sedge (Carex arenaria L.), the sand oat (Avena strigosa) and the couch grass (Agropyron Gardening).

Sandy landscapes offer a habitat for many plants and animals, for example on the Franconian sand axis. At the bottom of bodies of water, microorganisms colonize the sand gap system.

Soil formation on sand

Pure sandy soil is one of the least fertile soil types in Central Europe, as in this country it consists for the most part of quartz. Minerals that can release or store nutrients when weathered are therefore hardly available. Podsols or podsol-like brown earths are therefore preferred as soil. It is therefore often used for forestry and mostly bears pine forests, as in Brandenburg. Heather is also very well adapted to the dry locations and has therefore been introduced into the sandy landscapes by humans. Originally, however, the widespread beech or oak-birch mixed forests stood here as well.

use

Furthermore, sand is of economic importance for the following areas:

  • As filling sand in civil engineering, for backfilling pits and for modeling embankments in road construction.
  • As a raw material for glass production
  • Quartz-rich sand is a raw material for cement production
  • Sand is an essential additive in building materials such as concrete and lime mortar
  • As a joint filler for paving stones and paving stones
  • Stucco is a sand-containing, easily malleable mass that is used as a material for the interior and facade decoration of buildings
  • Silicon-rich sand is used as a raw material for the manufacture of semiconductors
  • As a grinding, scouring and polishing agent
  • Quartz sand is used as an abrasive in shot peening ("sandblasting"). Fine-grain corundum is increasingly being used as a substitute, as the silicate dust can cause silicosis ("dust lung")
  • As molding sand for metal casting
  • Since sand has a relatively large pore volume, underground sand and sandstone deposits are important as storage media for drinking water, crude oil and natural gas; Above ground, sand can also be of economic importance as oil sand
  • In drainage technology, sand is important as a filter material in wastewater treatment, for example in retention soil filters
  • For tourism, sand is a special attraction when there are superficial deposits of sand in the form of sandy beaches and dunes on the coast
  • Bird sand is used as bedding in bird cages. Among other things, it serves as a digestive aid for the birds.
  • As a design element in landscape planning, horticulture, sports and children's playgrounds (sandpit)
  • certain types of sand can be used as building material for sand sculptures.
  • Rail vehicles usually have sand spreaders for spreading brake sand to increase the frictional resistance between wheel and rail in locomotives
  • as sand to increase the frictional resistance on black ice
  • in the past (typically 17th or 18th century) as writing sand (also called scattering sand) to dry the wet ink (later blotting paper was used)

"Sand" in idioms

A number of idioms use the word "sand" as a rhetorical figure. It is noticeable that the term sand usually has a negative connotation:

  • Throw sand in someone's eyes for "deceiving someone"
  • Put something in the sand for "causing a failure"
  • sand in the gears for "a disturbed process"
  • Like sand at the ocean for "uncountable numbers"
  • Put your head in the sand for "not wanting to see a danger" or "giving up early"
  • Be built on sand for "having an uncertain basis"
  • Fizzled out for "a fruitless end"

literature

  • Raymond Siever: Sand. An archive of the history of the earth. Publishing house spectrum of science ISBN 3922508952

See also

Fulgurite, static friction, friction angle, sand bank, sand castle, sander, sand trap, sand trousers, sandman, sand rose, sandbag, sandstone, sand storm, hourglass, quicksand, thermal conductivity properties

Category: Sedimentary Rock