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A '''crystal''' or crystalline solid is a solid [[material]], whose constituent [[atoms]], [[molecule]]s, or ions are arranged in an orderly repeating [[pattern]] extending in all three spatial [[dimension]]s. The [[scientific]] [[study]] of crystals and crystal formation is [http://en.wikipedia.org/wiki/Crystallography crystallography]. The [[process]] of crystal formation via [[mechanism]]s of crystal [[growth]] is called crystallization or solidification. The word crystal is derived from the ancient Greek word κρύσταλλος (krustallos), which had the same [[meaning]], but according to the ancient understanding of crystal. At root it means anything congealed by freezing, such as ice.[1] The word once referred particularly to quartz, or "rock crystal".

A '''crystal''' or crystalline solid is a solid [[material]], whose constituent [[atoms]], [[molecule]]s, or ions are arranged in an orderly repeating [[pattern]] extending in all three spatial [[dimension]]s. The [[scientific]] [[study]] of crystals and crystal formation is [http://en.wikipedia.org/wiki/Crystallography crystallography]. The [[process]] of crystal formation via [[mechanism]]s of crystal [[growth]] is called crystallization or solidification. The word crystal is derived from the ancient Greek word κρύσταλλος (krustallos), which had the same [[meaning]], but according to the ancient understanding of crystal. At root it means anything congealed by freezing, such as ice.[1] The word once referred particularly to quartz, or "rock crystal".

Most metals encountered in everyday life are [http://en.wikipedia.org/wiki/Polycrystal polycrystals]. Crystals are often [[symmetrically]] intergrown to form crystal twins.

Most metals encountered in everyday life are [http://en.wikipedia.org/wiki/Polycrystal polycrystals]. Crystals are often [[symmetrically]] intergrown to form crystal twins.

==Crystal structure==

==Crystal structure==

The process of forming a crystalline [[structure]] from a fluid or from materials dissolved in the fluid is often referred to as crystallization. In the ancient example referenced by the root [[meaning]] of the word crystal, water being cooled undergoes a [[phase change]] from liquid to solid beginning with small ice crystals that grow until they [[fuse]], forming a polycrystalline structure. The [[physical]] properties of the ice depend on the size and arrangement of the individual crystals, or grains, and the same may be said of metals solidifying from a molten state.

The process of forming a crystalline [[structure]] from a fluid or from materials dissolved in the fluid is often referred to as crystallization. In the ancient example referenced by the root [[meaning]] of the word crystal, water being cooled undergoes a [[phase change]] from liquid to solid beginning with small ice crystals that grow until they [[fuse]], forming a polycrystalline structure. The [[physical]] properties of the ice depend on the size and arrangement of the individual crystals, or grains, and the same may be said of metals solidifying from a molten state.