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Molecular Structure Laboratory
How do crystal form?
It’s a very interesting question, considering that crystals are everywhere - they cool our beverages, run our digital clocks, adorn crowns of the kings. In fact the entire earth crust is made of crystals.
A crystal is an anisotropic, homogeneous solid consisting of a three-dimensional periodic ordering of atoms, molecules, or ions.
Crystal form by a dynamic process called crystallization that signifies transition from chaos to perfection. Unlike living organisms, crystal do not draw nourishment from within, but rather they grow by deposition of like material from the outside to the crystal surface. Crystals grow in one of three major ways: from a vapor, from a solution, or from a melt. In all cases the crystal growth is a three-stage process.
It begins with nucleation, in which a few molecules or ions approached each other in an appropriate orientation to form a stable submicroscopic aggregate.
The second stage is growth, which is an orderly addition of further molecules of ions in a regular manner. The crystal owes its shape to the orderly array of the atoms which compose it. The symmetry of the crystal shapes is their most recognizable feature.
In the final stage, termination, growth stops. At this stage the appearance of a crystal grown under specific conditions (known as habit) can be evaluated. The habit is evident in the relative development of the different faces of a crystal for a given material.
It is instructive to estimate how rapidly molecules must order themselves at the surface of a growing crystal. Even when the crystal growth rate is as slow as 1/10 of an inch per day, about a hundred layers of molecules must be laid down per second on the crystal surface.
There is no limit to how large a crystal one can grow – there is only limit to our patience and material supply. The largest crystal ever found is believed to be a beryl from Malakialina, Madagascar. It measures 59 feet long and 11 feet across, and weighs 380 tons.
The text above cites or based on the following sources: "Crystallography" by Walter Borchardt-Ott, "Crystals and crystal growing" by Alan Holden and Phylis Morrison, "Crystals and light" by Elizabeth Wood, and "X-ray crystallography" by Gregory Girolami.