Crystallization occurs when a solid precipitates from a liquid solution or gas. It can occur naturally or in a lab/industrial setting. Crystals form when a solute reaches supersaturation, and nucleation occurs. Crystals can form slowly, as in stalactites, or quickly, as in snowflakes. Salt and gemstones are examples of crystals. Humans can create crystals artificially, and many materials are produced by crystallization.
Crystallization is the formation of crystals that occurs when a solid precipitates from a liquid solution or, rarely, directly from a gas. The term is used to describe this process in nature as well as when it occurs in a laboratory or industrial setting. Mineral and organic compounds and even water can be crystallized. Most crystals are some type of compound, but crystals of pure elements are possible. Snowflakes, salt and some gemstones are formed from this process.
Crystals form when the concentration of a solute reaches a maximum, a condition called supersaturation. Cooling or evaporation of the solution will then activate the crystallization process. A reduction in temperature can trigger crystal formation because the ability of a solution to hold a solute depends in part on temperature. As the temperature decreases, the solubility also decreases. Evaporation increases the concentration of the solute in the solution, triggering crystallization.
The first stage in the formation of any crystal is called nucleation. Nucleation is the combination of two or more solute molecules. These molecules will attract more molecules, which will bond with the original crystals in a regular pattern. This pattern structure, or matrix, depends on the molecular properties of the substance being crystallized, but will continue to propagate in a regular fashion as more molecules are added. This process can continue even after the concentration of the dissolved solute drops below the supersaturation point, as the crystal will continue to add more molecules to its matrix.
The most commonly known crystallization process is the formation of water crystals in the atmosphere. This occurs all over the world, continuously, as air containing water vapor is cooled. water crystallizes into ice, and as the water crystals grow, they form snowflakes.
Crystallization can also occur very slowly. Stalactite formation in caves is a form of crystal formation that occurs over many centuries or even millions of years. As the water that holds the dissolved minerals flows over the surface of the stalactite, the molecules of these minerals bond with other molecules, adding very gradually to the stalactite.
Ancient peoples from all over the world obtained salt from the formation of salt crystals from the evaporation of sea water. This practice is still employed today as a cheap and effective way of obtaining salt. Salt crystals are mined in some areas of the world from immense deposits, sometimes thousands of feet thick, that remain from the evaporation of prehistoric seas.
Other crystals are highly sought after and mined for their value as gemstones. While not all gems are crystals, many form deep within the earth over a period of thousands or millions of years. Many types of crystals are created artificially by humans, but all of these processes are based on the same chemical principles that form natural crystals. Many foods, minerals and industrial materials are produced by crystallization.
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