Editing Crystal (section)

== Chemical bonds ==
In general, solids can be held together by various types of [[chemical bond]]s, such as [[metallic bond]]s, [[ionic bond]]s, [[covalent bond]]s, [[van der Waals bond]]s, and others. None of these are necessarily crystalline or non-crystalline. However, there are some general trends as follows:

[[Metal]]s crystallize rapidly and are almost always polycrystalline, though there are exceptions like [[amorphous metal]] and single-crystal metals. The latter are grown synthetically, for example, fighter-jet turbines are typically made by first growing a single crystal of titanium alloy, increasing its strength and melting point over polycrystalline titanium. A small piece of metal may naturally form into a single crystal, such as Type 2 [[telluric iron]], but larger pieces generally do not unless extremely slow cooling occurs. For example, iron [[meteorite]]s are often composed of single crystal, or many large crystals that may be several meters in size, due to very slow cooling in the vacuum of space. The slow cooling may allow the precipitation of a separate phase within the crystal lattice, which form at specific angles determined by the lattice, called [[Widmanstatten pattern]]s.<ref>''Encyclopedia of the Solar System'' by Tilman Spohn, Doris Breuer, Torrence V. Johnson -- Elsevier 2014 Page 632</ref>

[[Ionic compound]]s typically form when a metal reacts with a non-metal, such as sodium with chlorine. These often form substances called salts, such as sodium chloride (table salt) or potassium nitrate ([[saltpeter]]), with crystals that are often brittle and cleave relatively easily. Ionic materials are usually crystalline or polycrystalline. In practice, large [[salt (chemistry)|salt]] crystals can be created by solidification of a [[molten]] fluid, or by crystallization out of a solution. Some ionic compounds can be very hard, such as oxides like [[aluminium oxide]] found in many gemstones such as [[ruby]] and [[synthetic sapphire]].

[[Covalently bonded]] solids (sometimes called [[covalent network solids]]) are typically formed from one or more non-metals, such as carbon or silicon and oxygen, and are often very hard, rigid, and brittle. These are also very common, notable examples being [[diamond]] and [[quartz]] respectively.<ref>[https://www.angelo.edu/faculty/kboudrea/general/formulas_nomenclature/Formulas_Nomenclature.htm#:~:text=Ionic%20compounds%20are%20(usually)%20formed,nonmetals%20react%20with%20each%20other. Angelo State University: Formulas and Nomenclature of Ionic and Covalent Compounds]</ref>

Weak [[van der Waals force]]s also help hold together certain crystals, such as crystalline [[molecular solid]]s, as well as the interlayer bonding in [[graphite]]. Substances such as [[fat]]s, [[lipid]]s and [[wax]] form molecular bonds because the large molecules do not pack as tightly as atomic bonds. This leads to crystals that are much softer and more easily pulled apart or broken. Common examples include chocolates, candles, or viruses. Water ice and [[dry ice]] are examples of other materials with molecular bonding.<ref>''Science for Conservators, Volume 3: Adhesives and Coatings'' by Museum and Galleries Commission -- Museum and Galleries Commission 2005 Page 57</ref>[[Polymer]] materials generally will form crystalline regions, but the lengths of the molecules usually prevent complete crystallization—and sometimes polymers are completely amorphous.