How are Crystals Formed

Crystals are basically solids that are formed by the orderly and repeated arrangement of constituent elements like atoms, ions or molecules. The word 'crystal' is derived from the Greek word, krustallos, that has the same meaning, but once referred to as quartz and rock crystals.

Types of Crystals
Crystals can be classified into different types depending on their shape and properties. Based on their shape, they are divided into seven types, namely cubic or isometric, tetragonal, orthorhombic, hexagonal, rhombohedral, monoclinic and triclinic crystals.
On the basis of their physical and chemical properties, crystals are classified into the following four types: covalent, metallic, molecular and ionic.

How are Crystals Formed
The process of crystal formation is known as crystallization. Crystallization is the process of formation of crystals from solutions, molten substances and even gas. The process can be divided into two main stages, namely nucleation and crystal growth.

Nucleation involves the accumulation of solute dissolved in the solvent into clusters. However, the clusters should be stable to ensure the formation of crystals, otherwise they get redissolved in the solution. The stable clusters form the nuclei. For forming stable nuclei, the clusters have to attain a critical size determined by the operating conditions, like temperature and supersaturation (refers to a solution containing more of the dissolved material than that could be dissolved under normal conditions). At this stage of nucleation, atoms get arranged in geometrical shape in a periodic or repeated manner, which plays a significant role in determining the structure of the crystals.

The next stage of crystallization is crystal growth, which involves the growth of the stable nuclei. This helps the crystals to attain the critical cluster size, after which it can no longer dissolve in the solution. Nucleation and crystal growth takes place simultaneously as long as supersaturation exists. So, the most important condition for crystallization is the existence of supersaturation, as it determines the rate of nucleation and crystal growth. When supersaturation ceases to exist, the solid-liquid system attains equilibrium and the process of crystallization comes to an end.

Crystals are generally formed when magma or molten rock cools and solidifies. Rapid cooling of the molten rock generally results in the formation of small crystals. However, if they cool down slowly, then large crystals are formed. Some crystals like diamonds are formed deep in the earth from the carbon atoms present in the molten rocks. The high pressure and intense heat causes the carbon atoms to come together to form small diamond crystals, that are held in molten rock.

Crystals can be formed due to evaporation. When you dissolve a soluble substance or solute in a solvent, the crystal structure of the substance breaks down into individual atoms, ions or molecules and gets dissolved in the solution. When evaporation takes place the amount of solution available for dissolution gets reduced. This in turn causes the excess solute to gather into clusters and crystallize.

Crystallization can be augmented by changing the temperature of the solvent. Generally, solubility can be reduced by lowering the temperature of the solvent, which helps in the formation of crystals. The rate of crystallization can also be increased by changing the nature of the solvent. This can be done by adding a non-solvent to the solution, which reduces solubility and hence ensures rapid crystallization.

These shining, glittering crystals have a wide range of application. Crystals like diamonds, emeralds, rubies and other gemstones are known for their dazzling beauty, while others like, sugar and salt are indispensable part of human diet. They can also be used for healing purposes, known as crystal healing, an important part of astrology. Crystals are able to hold electric charge, which facilitates the healing work. They are also capable of enhancing the energy fields of the body by emitting uniform vibrations. Quartz is another important crystal that is nowadays used in computers, watches and radio stations for its astounding and constant energy field.