The study of crystals and their structure is a field called Crystallography. A crystal is a solid that consists of the various atoms or molecules being arranged in a uniform repeating pattern based on its unique shape. This results in the material having a specific shape and color, and having other characteristic properties.

Crystals may be big or little, but they all have the same "shape". Take a look at the display of crystals in the lab. Salt and sugar are examples of crystals. Table salt is NaCl and has a cube-shaped structure. Snow crystals form a six-sided structure. A diamond (used in jewelery, and cutting tools) is also an example of a crystal; it is made of pure carbon. Graphite (used in pencils and lubricants) is also a crystal made from carbon.

In a solution, a solvent(water) can only hold a certain amount of solute. This is called the solubility of a solution. When the temperature of the solution is increased, hot water can dissolve more solid substance than cold water. This is because heated water molecules move farther apart, making room for more solid substance to dissolve. When no more of the solid substance can be dissolved, the solution is said to be saturated. As this solution cools, the water molecules move closer together again and there's less room for the solution to hold onto as much of the dissolved solid. Crystals begin to form and build on one another as the water lets go of the excess solute. This process is called recrystallization.