What is Crystal?
[[File:Quartz oisan.jpg|thumb|250px|[[Quartz]] crystal]] A '''crystal''' is a [[solid]] whose [[atoms]] (or [[molecule]]s) are arranged in a repeating pattern. Crystals are made from fluids by [[Crystallization]], which is a kind of [[phase change]]. Usually the fluid is a [[liquid]], but crystals can form from a [[gas]] too. For example, [[snow]] is water crystals ([[ice]]) formed from air that contains [[water vapor]] ([[evaporation|evaporated]] water). [[Crystallization]] can be by [[freezing]] from a simple fluid or from a [[solution]]. Sometimes heat and [[pressure]] needs to be applied to a substance for crystals to form. [[Diamond]] is a [[carbon]] crystal formed under heat and pressure. Crystals are found naturally or can be made artificially. The surface of crystals often have regions that are flat, called facets. Facets occur naturally as crystals form, because flat layers of atoms are usually the most stable. The atoms in a facet are arranged in a regular pattern, such as the pattern of a [[chess]] board or a [[honeycomb]]. These facets reflect light to give crystals their shiny or sparky appearance. Artificial facets can be made in any shape by cutting or grinding a crystal, which is how some [[gemstones]] for jewelry are made. Different substances form different types of crystals, and some can form more than one type. The study of the arrangement of atoms in crystals is [[crystallography]]. Well-known substances that form crystals are [[table salt]] (whose crystals are [[cube]]s), [[diamond]], and [[quartz]]. [[Image:Sodium chloride crystal.png|thumb|250px|[[Atom]]s (as [[ion]]s) in a crystal of [[sodium chloride]] (table salt). The blue ions are [[sodium]] and the green ions are [[chloride]]]] ==Related pages== *[[Crystallization]] *[[Crystallography]] *[[Liquid crystal]] *[[Crystal structure]] ==More reading== * {{cite book |last1=Iggulden |first1=Hal |last2=Iggulden |first2=Conn |title=The Dangerous Book for Boys |date=2007 |publisher=HarperCollins |location=New York |isbn=978-0061243585