A crystal or crystalline solid is a solid Solid is one of the major states of matter. It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a gas does. The atoms in a solid are tightly bound to each other, material, whose constituent atoms The atom is a basic unit of matter that consists of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons . The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain, molecules A molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense. In organic chemistry and biochemistry, the term molecule is used less strictly and also is applied to charged organic molecules, or ions An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. An anion , from the Greek word ἀνω (anο), meaning "up", is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography Crystallography is the experimental science of determining the arrangement of atoms in solids. The word "crystallography" is derived from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and grapho = write. The process of crystal formation via mechanisms of crystal growth The crystalline state of matter is characterized by a distinct structural rigidity and virtual resistance to deformation . Most crystalline solids have high values both of Young's modulus and of the shear modulus of elasticity. This contrasts with most liquids or fluids, which have a low shear modulus, and typically exhibit the capacity for is called crystallization Crystallization is the process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas. Crystallization is also a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs or solidification. The word crystal is derived from the Ancient Greek Ancient Greek is the historical stage in the development of the Greek language spanning the Archaic , Classical (c. 5th–4th centuries BC), and Hellenistic (c. 3rd century BC – 6th century AD) periods of ancient Greece and the ancient world. It is predated in the 2nd millennium BC by Mycenaean Greek. Its Hellenistic phase is known as Koine (& word κρύσταλλος (krustallos), meaning "rock-crystal" but also "ice",^[1] from κρύος (kruos), "icy cold, frost".^[2][3] The word once referred particularly to quartz Quartz is the second most abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2, or "rock crystal".

Most metals encountered in everyday life are polycrystals Polycrystalline materials are solids that are composed of many crystallites of varying size and orientation. The variation in direction can be random or directed, possibly due to growth and processing conditions. Fiber texture is an example of the latter. Crystals are often symmetrically intergrown to form crystal twins.

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 Crystallization is the process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas. Crystallization is also a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs. In the old 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.

Which crystal structure In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry. Patterns are located upon the points of a lattice, which is an array the fluid A fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids will form depends on the chemistry Chemistry is the science of matter and the changes it undergoes. The science of matter is also addressed by physics, but while physics takes a more general and fundamental approach, chemistry is more specialized, being concerned with the composition, behavior, structure, and properties of matter, as well as the changes it undergoes during chemical of the fluid, the conditions under which it is being solidified, and also on the ambient pressure The ambient pressure on an object is the pressure of the surrounding medium, such as a gas or liquid, which comes into contact with the object. While the cooling process usually results in the generation of a crystalline material, under certain conditions, the fluid may be frozen in a noncrystalline state. In most cases, this involves cooling the fluid so rapidly that atoms The atom is a basic unit of matter that consists of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons . The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain cannot travel to their lattice Two Bravais lattices are often considered to be equivalent if they have isomorphic symmetry groups. In this sense, there are 14 possible Bravais lattices in three-dimensional space. The 14 possible symmetry groups of Bravais lattices are 14 of the 230 space groups sites before they lose mobility. A noncrystalline material, which has no long-range order In physics, long-range order characterizes physical systems in which remote portions of the same sample exhibit correlated behavior, is called an amorphous An "amorphous solid" is a solid in which there is no long-range order of the positions of the atoms. . Most classes of solid materials can be found or prepared in an amorphous form. For instance, common window glass is an amorphous solid, many polymers (such as polystyrene) are amorphous, and even junkfoods such as cotton candy are, vitreous, or glassy Glass is an amorphous solid material. Glasses are typically brittle, and often optically transparent. Glass is commonly used for windows, bottles, and eyewear; examples of glassy materials include soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovy-glass, and aluminium oxynitride. The term glass developed in the late Roman material. It is also often referred to as an amorphous solid, although there are distinct differences between crystalline solids and amorphous solids: most notably, the process of forming a glass does not release the latent heat of fusion The standard enthalpy of fusion , also known as the heat of fusion or specific melting heat, is the amount of thermal energy which must be absorbed or evolved for 1 mole of a substance to change states from a solid to a liquid or vice versa. It is also called the latent heat of fusion or the enthalpy change of fusion, and the temperature at which.

Crystalline structures occur in all classes of materials, with all types of chemical bonds A chemical bond is an attraction between atoms or molecules and allows the formation of chemical compounds, which contain two or more atoms. A chemical bond is the attraction caused by the electromagnetic force between opposing charges, either between electrons and nuclei, or as the result of a dipole attraction. The strength of bonds varies. Almost all metal Metallic bonding is the electromagnetic interaction between delocalized electrons, called conduction electrons and gathered in an "electron sea", and the metallic nuclei within metals. Understood as the sharing of "free" electrons among a lattice of positively-charged ions , metallic bonding is sometimes compared with that of exists in a polycrystalline state; amorphous or single-crystal metals must be produced synthetically, often with great difficulty. Ionically bonded An ionic bond is a type of chemical bond that involves a metal and a nonmetal ion through electrostatic attraction. In short, it is a bond formed by the attraction between two oppositely charged ions crystals can form upon solidification of salts Salt is a mineral that is composed primarily of sodium chloride. It is essential for animal life in small quantities, but is harmful to animals and plants in excess. Salt flavor is one of the basic tastes, making salt one of the oldest, most ubiquitous food seasonings. Salting is an important method of food preservation, either from a molten Melting, or fusion, is a physical process that results in the phase change of a substance from a solid to a liquid. The internal energy of a substance is increased, typically by the application of heat or pressure, resulting in a rise of its temperature to the melting point, at which the rigid ordering of molecular entities in the solid breaks fluid or upon crystallization from a solution. Covalently A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, and other covalent bonds. In short, the attraction-to-repulsion stability that forms between atoms when they share electrons is known as covalent bonding bonded crystals are also very common, notable examples being diamond In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions. Diamond is renowned as a material with superlative, silica The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with a chemical formula of Si , and graphite The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek γράφειν : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead. Unlike diamond (another carbon allotrope), graphite is an electrical. Polymer A polymer is a large molecule composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a wide variety of properties materials generally will form crystalline regions, but the lengths of the molecules usually prevent complete crystallization. Weak van der Waals forces In physical chemistry, the van der Waals force , named after Dutch scientist Johannes Diderik van der Waals, is the attractive or repulsive force between molecules (or between parts of the same molecule) other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral molecules. The term includes: can also play a role in a crystal structure; for example, this type of bonding loosely holds together the hexagonal In geometry, a hexagon is a polygon with six edges and six vertices. A regular hexagon has Schläfli symbol {6}. The total of the internal angles of any hexagon is 720 degrees-patterned sheets in graphite.

Most crystalline materials have a variety of crystallographic defects Crystalline solids have a very regular atomic structure: that is, the local positions of atoms with respect to each other are repeated at the atomic scale. These arrangements are called crystal structures, and their study is called crystallography. However, most crystalline materials are not perfect: the regular pattern of atomic arrangement is. The types and structures of these defects can contain a profound effect on the properties of the materials.

Crystalline phases

• Polymorphism Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to elemental solids. The complete morphology of a material is described by is the ability of a solid to exist in more than one crystal form. For example, water ice Ice, technically, is one of the 15 known crystalline phases of water. In non-scientific contexts, the term usually means ice Ih, which is known to be the most abundant of these solid phases. It can appear transparent or opaque bluish-white colour, depending on the presence of impurities or air inclusions. The addition of other materials such as is ordinarily found in the hexagonal form Ice I_h Ice Ih is the hexagonal crystal form of ordinary ice, or frozen water. Virtually all ice in the biosphere is ice Ih, with the exception only of a small amount of ice Ic which is occasionally present in the upper atmosphere. Ice Ih exhibits many peculiar properties which are relevant to the existence of life and regulation of global climate, but can also exist as the cubic Ice I_c Ice Ic is a metastable cubic crystalline variant of ice. The oxygen atoms are arranged in a diamond structure. It is produced at temperatures between 130-150 K, and is stable for up to 200 K, when it transforms into ice Ih. It is occasionally present in the upper atmosphere, the rhombohedral In crystallography, the trigonal crystal system is one of the seven crystal systems, and the rhombohedral lattice system is one of the seven lattice systems. They are often confused with each other: crystals in the rhombohedral lattice system are always in the trigonal crystal system, but some crystals such as quartz are in the trigonal crystal ice II Ice II is a rhombohedral crystalline form of ice with highly ordered structure. It is formed from ice Ih by compressing it at temperature of 198 K at 300 MPa or by decompressing ice V. When heated it undergoes transformation to ice III, and many other forms.
• Amorphous An "amorphous solid" is a solid in which there is no long-range order of the positions of the atoms. . Most classes of solid materials can be found or prepared in an amorphous form. For instance, common window glass is an amorphous solid, many polymers (such as polystyrene) are amorphous, and even junkfoods such as cotton candy are phases are also possible with the same molecule, such as amorphous ice Amorphous ice is an amorphous solid form of water, meaning it consists of water molecules that are randomly arranged like the atoms of common glass. Everyday ice is a polycrystalline material. Amorphous ice is distinguished by its lack of long-range order. Amorphous ice is produced by cooling liquid water prodigiously quickly , so the molecules. In this case, the phenomenon is known as polyamorphism Polyamorphism is the ability of a substance to exist in several different amorphous modifications. It is analogous to the polymorphism of crystalline materials. Many amorphous substances can exist with different amorphous characteristics . However, polyamorphism requires two distinct amorphous states with a clear (first-order) phase transition.
• For pure chemical elements, polymorphism is known as allotropy Allotropy or allotropism is the property of some chemical elements to exist in two or more different forms, known as allotropes of these elements. Allotropes are different structural modifications of an element; the element's atoms are bonded together in a different manner. For example, diamond In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions. Diamond is renowned as a material with superlative, graphite The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Greek γράφειν : "to draw/write", for its use in pencils, where it is commonly called lead, as distinguished from the actual metallic element lead. Unlike diamond (another carbon allotrope), graphite is an electrical, and fullerenes are different allotropes of carbon.

Special cases

Since the initial discovery of crystal-like individual arrays of atoms that are not regularly repeated, made in 1982 by Dan Shechtman, the acceptance of the concept and the word quasicrystal have led the International Union of Crystallography to redefine the term crystal to mean "any solid having an essentially discrete diffraction diagram", thereby shifting the essential attribute of crystallinity from position space to Fourier space. Within the family of crystals one distinguishes between traditional crystals, which are periodic, or repeating, at the atomic scale, and aperiodic (incommensurate) crystals which are not. This broader definition adopted in 1996 reflects the current understanding that microscopic periodicity is a sufficient but not a necessary condition for crystals.

While the term "crystal" has a precise meaning within materials science and solid-state physics, colloquially "crystal" refers to solid objects that exhibit well-defined and often pleasing geometric shapes. In this sense of the word, many types of crystals are found in nature. The shape of these crystals is dependent on the types of molecular bonds between the atoms to determine the structure, as well as on the conditions under which they formed. Snowflakes, diamonds, and table salt are common examples of crystals.

Some crystalline materials may exhibit special electrical properties such as the ferroelectric effect or the piezoelectric effect. Additionally, light passing through a crystal is often refracted or bent in different directions, producing an array of colors; crystal optics is the study of these effects. In periodic dielectric structures a range of unique optical properties can be expected as seen in photonic crystals.

Crystalline rocks

Inorganic matter, if free to take that physical state in which it is most stable, tends to crystallize. There is no practical limit to the size a crystal may attain under the right conditions, and selenite single crystals in excess of 10 m are found in the Cave of the Crystals in Naica, Mexico.^[4]

Crystalline rock masses have consolidated from aqueous solution or from molten magma. The vast majority of igneous rocks belong to this group and the degree of crystallization depends primarily on the conditions under which they solidified. Such rocks as granite, which have cooled very slowly and under great pressures, have completely crystallized, but many lavas were poured out at the surface and cooled very rapidly; in this latter group a small amount of amorphous or glassy matter is frequent. Other crystalline rocks, the evaporites such as rock salt, gypsum and some limestones have been deposited from aqueous solution, mostly owing to evaporation in arid climates. Still another group, the metamorphic rocks which includes the marbles, mica-schists and quartzites; are recrystallized, that is to say, they were at first fragmental rocks, like limestone, shale and sandstone and have never been in a molten condition nor entirely in solution. The high temperature and pressure conditions of metamorphism have acted on them erasing their original structures, and inducing recrystallization in the solid state.^[5]

Properties

See also

• Atomic packing factor
• Colloidal crystal
• Crystal growth
• Crystal habit
• Crystal oscillator
• Crystal system
• Crystallite
• Crystallographic database
• Liquid crystal
• Quasicrystal

References

1. ^ κρύσταλλος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
2. ^ κρύος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
3. ^ "kreus-". The American Heritage Dictionary of the English Language: Fourth Edition: Appendix I: Indo-European Roots. 2000. http://www.bartleby.com/61/roots/IE243.html .
4. ^ National Geographic, 2008. Cavern of Crystal Giants
5. ^ This article incorporates text from the article "Petrology" in the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.

Further reading

• Howard, J. Michael; Darcy Howard (Illustrator) (1998). "Introduction to Crystallography and Mineral Crystal Systems". Bob's Rock Shop. http://www.rockhounds.com/rockshop/xtal/index.html. Retrieved 2008-04-20.
• Krassmann, Thomas (2005–2008). "The Giant Crystal Project". Krassmann. http://giantcrystals.strahlen.org. Retrieved 2008-04-20.
• Various authors (2007). "Teaching Pamphlets". Commission on Crystallographic Teaching. http://www.iucr.ac.uk/iucr-top/comm/cteach/pamphlets.html. Retrieved 2008-04-20.
• Various authors (2004). "Crystal Lattice Structures:Index by Space Group". U.S. Naval Research Laboratory, Center for Computational Materials Science. http://cst-www.nrl.navy.mil/lattice/spcgrp/. Retrieved 2008-04-20.
• Various authors (2010). "Crystallography". Spanish National Research Council, Department of Crystallography. http://www.xtal.iqfr.csic.es/Cristalografia/index-en.html. Retrieved 2010-01-08.

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