A crystal is a solid whereby the constituent ions, atoms or molecules are concentrated together in a regular order and repeating this order or pattern in all three dimensional spaces. The term "crystal" comes from the Greek word Krystallos which means clear ice. Crystals are formed when there is some sort of solidification. In ideal conditions, the crystal formed maybe a single crystal but there are many instances of crystals being formed with lots of different crystals inside. These are commonly known as polycrystals.

The formation of a crystal depends entirely on what the liquid is to begin with and what kind of situation will it be in when it solidifies such as location, pressure, and other chemicals in the atmosphere. The formation process of a crystal is known as crystallization. The cooling process creates the generation of crystalline material and sometimes the fluid is frozen in a noncrystalline state. If this is the case, it involves the fluid cooling down at such rapid speed that the atoms cannot travel to their designated sites before they cannot move anymore.

Crystals occur in all different types of materials and exist different chemical bonds. Polycrystalline crystals have some type of metal inside. Most crystalline materials have a range of defects, which can have an effect on the different properties of the materials.

Although the term crystal is used to define solids with ions, atoms or molecules that forma regulated pattern, it is generally referred to something of a rocklike structure with a pattern that is pleasing to the eye. In this sense of the word, many types of crystals are found in nature. The shape and chemical structure are key influences as to how the crystal is formed and what kind of structures and patterns it holds. Snowflakes, salt and diamonds are mainstream examples of crystals.

Some crystals have various degrees of electrical attributes to them such as the ferroelectric effect or the piezoelectric effect. Additionally, crystals tend to be quite spectacular when light is passed through them, refracting the light into an array of different colors.

Inorganic matter generally crystallizes if it is free to do so. Rock masses have consolidated from such things as solution or fusion. Igneous rocks belong to this group and as to how perfectly formed they are depends on what conditions they were formed under. This is to do with the chemicals involved, the surrounding environment and the location. Rocks such granite that have cooled down over a long period of time and under great pressure are completely crystallized but many lavas were poured on the surface and cooled down very quickly. In this last group a little amount of noncrystalline matter is fairly common. Other rocks that have been crystallized such as rock salt, gypsum and anhydrite have been deposited into water due to evaporation or exposure.

Crystals nowadays are being used in alternative treatments for healing purposes. They are used because so physicians believe that crystals have energies embedded in them that can be transferred to humans for healing processes. It is known as crystal therapy and usually involves the patient lying down and various crystals being put on specific parts of the body. This type of treatment is known as alternative due to the lack of scientific evidence to prove that it is beneficial in any way. It is known that crystals, from a scientific point of view, can be a conductor of energy through electricity, but there is no evidence to suggest that they hold other healing energies and even less to suggest that it can be passed on to humans.