crystal

1. 1. A homogenous solid formed by a repeating, three-dimensional pattern of atoms, ions, or molecules and having fixed distances between constituent parts.
   2. The unit cell of such a pattern.
2. A mineral, especially a transparent form of quartz, having a crystalline structure, often characterized by external planar faces.
3. 1. A natural or synthetic crystalline material having piezoelectric or semiconducting properties.
   2. An electronic device, such as an oscillator or detector, using such a material.
4. 1. A high-quality, clear, colorless glass.
   2. An object, especially a vessel or ornament, made of such glass.
   3. Such objects considered as a group.
5. A clear glass or plastic protective cover for the face of a watch or clock.
6. Slang. A stimulant drug, usually methamphetamine, in its powdered form.

[Middle English cristal, from Old French, from Latin crystallum, from Greek krustallos, ice, crystal.]

For more information on crystal, visit Britannica.com.

A solid in which the atoms or molecules are arranged periodically. Within a crystal, many identical parallelepiped unit cells, each containing a group of atoms, are packed together to fill all space (see illustration). In scientific nomenclature, the term crystal is usually short for single crystal, a single periodic arrangement of atoms. Most gems are single crystals. However, many materials are polycrystalline, consisting of many small grains, each of which is a single crystal. For example, most metals are polycrystalline. See also Single crystal.

Structure of a simple crystal. Spheres, representing atoms, are packed together into a cubic lattice. This crystal has 4-fold symmetry axes passing through the front face; after a 90° rotation the structure appears unchanged.

In electronics, the term crystal is restricted to mean piezoelectric crystal. Piezoelectric crystals contract or expand under application of electric voltages, and conversely they generate voltages when compressed. They are used for oscillators, pressure sensors, and position actuators. See also Piezoelectricity.

The anisotropic microscopic structure of a crystal is often reflected in its external form, consisting of flat faces and sharp edges. Crystal structure is generally determined via diffraction of x-rays, neutrons, or electrons. Unlike disordered materials such as glasses or liquids, the diffraction pattern of a periodic array of atoms consists of individual sharp spots. The symmetry and structure of the crystal can be inferred from the symmetry of the diffraction pattern and the intensities of the diffracted beams. See also Electron diffraction; Neutron diffraction; X-ray diffraction.

A crystal can be characterized by the symmetry operations that leave its structure invariant. These can include rotation about an axis through a specific angle, reflection through a plane, inversion through a point, translations by a unit cell dimension, and combinations of these. For a periodic structure, the only allowable rotational symmetries are 2-fold, 3-fold, 4-fold, and 6-fold. A quasicrystal is a solid which yields a sharp diffraction pattern but has rotational symmetries (such as 5-fold or 10-fold) which are inconsistent with a periodic arrangement of atoms. See also Quasicrystal.

A plastic crystal is generally composed of organic molecules which are rotationally disordered. The centers of the molecules lie at well-defined, periodically spaced positions, but the orientations of the molecules are random. Plastic crystals are often very soft and may flow under their own weight.

A liquid crystal is a material which is intermediate in structure between a liquid and a solid. Liquid crystals usually flow like liquids but have some degree of internal order. They are generally composed of rodlike organic molecules, although in some cases they are composed of disklike molecules. In a nematic liquid crystal, the rods all have the same general orientation, but the positions of the rods are disordered. In a smectic liquid crystal, rodlike molecules are ordered into sheets, within which there is only liquidlike order. A smectic can thus be thought of as being crystalline in one dimension and liquid in the other two. In a discotic liquid crystal, disklike molecules are ordered into columnar arrays; there is short-range liquidlike order within the columns, but the columns form a two-dimensional crystal. See also Crystal defects; Crystal growth; Crystal structure; Crystallography; Liquid crystals.

A transparent quartz material that contains a uniform arrangement of molecules. See crystalline and quartz crystal.

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Definition: clear, transparent
Antonyms: clouded, foggy

A material in which the atoms are arranged in a rigid geometrical structure (see geometry) marked by symmetry. Crystals often have clearly visible geometrical shapes.

Natural or synthetic piezoelectric or semiconductor material with atoms arranged with some degree of geometric regularity.

A crystal can represent something beautiful or even spiritual. Alternatively, it can mean something that has "crystallized," either in the sense of manifesting or in the sense of becoming rigid. We are also familiar with "crystal" balls that are used to divine the future.

This article is about crystalline solids. For the type of glass, see lead crystal. For other uses, see Crystal (disambiguation).

Quartz crystal. The individual grains of this polycrystalline mineral sample are clearly visible.

A crystal or crystalline solid is a solid material, whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography. The process of crystal formation via mechanisms 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 polycrystals. Crystals are often symmetrically intergrown to form crystal twins.

Contents 1 Crystal structure 2 Crystalline phases 3 Special cases 4 Crystalline rocks 5 Properties 6 See also 7 References 7.1 Further reading

Crystal structure

Insulin crystals

Halite (sodium chloride) - a single, large crystal.

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.

Which crystal structure the fluid will form depends on the chemistry of the fluid, the conditions under which it is being solidified, and also on the ambient pressure. 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 cannot travel to their lattice sites before they lose mobility. A noncrystalline material, which has no long-range order, is called an amorphous, vitreous, or glassy 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.

Crystalline structures occur in all classes of materials, with all types of chemical bonds. Almost all metal exists in a polycrystalline state; amorphous or single-crystal metals must be produced synthetically, often with great difficulty. Ionically bonded crystals can form upon solidification of salts, either from a molten fluid or upon crystallization from a solution. Covalently bonded crystals are also very common, notable examples being diamond, silica, and graphite. Polymer materials generally will form crystalline regions, but the lengths of the molecules usually prevent complete crystallization. Weak van der Waals forces can also play a role in a crystal structure; for example, this type of bonding loosely holds together the hexagonal-patterned sheets in graphite.

Most crystalline materials have a variety of crystallographic defects. The types and structures of these defects can have a profound effect on the properties of the materials.

Crystalline phases

See: Phase transformations in solids

• Polymorphism is the ability of a solid to exist in more than one crystal form. For example, water ice is ordinarily found in the hexagonal form Ice I_h, but can also exist as the cubic Ice I_c, the rhombohedral ice II, and many other forms.
• Amorphous phases are also possible with the same molecule, such as amorphous ice. In this case, the phenomenon is known as polyamorphism.
• For pure chemical elements, polymorphism is known as allotropy. For example, diamond, graphite, and fullerenes are different allotropes of carbon.

Special cases

A large monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA.

Gallium, a metal that easily forms large single crystals

Ice crystals

Fossil shell with calcite crystals

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.^[2]

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.^[3]

Properties

Crystal	Particles	Attractive forces	Melting point	Other properties
Ionic	Positive and negative ions	Electrostatic attractions	High	Hard, brittle, good electrical conductor in molten state
Molecular	Polar molecules	London force and dipole-dipole attraction	Low	Soft, non-conductor or extremely poor conductor of electricity in liquid state
Molecular	Non-polar molecules	London force	Low	Soft conductor

See also

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

References

1. ^ "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 .
2. ^ National Geographic, 2008. Cavern of Crystal Giants
3. ^ 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. 

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - krystal
adj. - krystal-

idioms:

• a crystal ball    krystalkugle
• crystal clear    indlysende
• crystal set    krystalapparat
• crystal system    krystalsystem

Nederlands (Dutch)
kristal, kristallen, horlogeglas, zo klaar als een klontje

Français (French)
n. - (Chim) cristal, cristal (de roche), cristal, verre
adj. - de cristal, en cristal, cristallin

idioms:

• crystal ball    boule de cristal
• crystal clear    clair, cristallin, limpide, clair comme de l'eau de roche, clair comme le jour
• crystal set    récepteur à cristal, récepteur à galène
• crystal system    réseau de cristaux

Deutsch (German)
n. - Kristall
adj. - kristallen

idioms:

• crystal ball    Glaskugel
• crystal clear    glasklar
• crystal set    primitives Radioempfangsgerät
• crystal system    Kristallsystem

Ελληνική (Greek)
n. - (ορυκτ., χημ.) κρύσταλλο(ς), (μτφ.) κρύσταλλο πλάκας ρολογιού
adj. - κρυστάλλινος, κρυσταλλικός, (μτφ.) διαφανέστατος

idioms:

• a crystal ball    γυάλινη σφαίρα (της κρυσταλλομαντείας)
• crystal clear    διαυγέστατος, (μτφ.) ολοφάνερος
• crystal set    ραδιοφωνικός δέκτης κρυστάλλου
• crystal system    κρυσταλλικό σύστημα

Italiano (Italian)
cristallo, cristallino

idioms:

• crystal ball    sfera di cristallo
• crystal clear    cristallino
• crystal set    radio a galena
• crystal system    sistema cristallino

Português (Portuguese)
n. - cristal (m)
adj. - cristalino

idioms:

• crystal ball    bola (f) de cristal
• crystal set    receptor (m) com detector de cristal
• crystal system    sistema (m) cristalino

Русский (Russian)
хрусталь, кристалл, хрустальный, кристальный

idioms:

• crystal ball    магический кристалл
• crystal set    детекторный приемник
• crystal system    семь комбинаций данных горного хрусталя

Español (Spanish)
n. - cristal
adj. - cristales de hielo, cristalino, de cristal

idioms:

• crystal ball    bola de cristal
• crystal clear    cristalino, límpido, más claro que el agua, obvio
• crystal set    receptor de cristal
• crystal system    sistema cristalino, forma de cristal

Svenska (Swedish)
n. - kristall, kristallglas, klockglas, kristallklart vatten (poet.)
adj. - kristall-, kristallklar

中文（简体）(Chinese (Simplified))
水晶, 结晶, 水晶装饰品, 水晶的, 透明的, 水晶一样的

idioms:

• a crystal ball    水晶球, 预言未来的方法
• crystal clear    清晰明了的, 显而易见的
• crystal set    晶体收音机
• crystal system    结晶系, 晶系

中文（繁體）(Chinese (Traditional))
n. - 水晶, 結晶, 水晶裝飾品
adj. - 水晶的, 透明的, 水晶一樣的

idioms:

• a crystal ball    水晶球, 預言未來的方法
• crystal clear    清晰明瞭的, 顯而易見的
• crystal set    晶體收音機
• crystal system    結晶系, 晶系

한국어 (Korean)
n. - 수정, 예언, 결정체
adj. - 수정의, 투명한, 결정의

idioms:

• a crystal ball    점쟁이의 수정 구슬

日本語 (Japanese)
n. - 水晶, クリスタルガラス, クリスタルガラス製品, 時計のガラスぶた, 結晶
adj. - 透き通った, 水晶の

idioms:

• a crystal ball    水晶球
• crystal ball    水晶球, 占いの方法
• crystal clear    とてもよく澄んだ, 明白な
• crystal set    鉱石受信器
• crystal system    結晶系

العربيه (Arabic)
‏(الاسم) بلور, زجاج بلوري (صفه) بلوري‏

עברית (Hebrew)
n. - ‮בדולח, גביש, זכוכית-השעון‬
adj. - ‮צח כבדולח, עשוי מגביש או דומה לו, שקוף‬

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