Crystal
A crystal or crystalline solid is a
The word crystal derives from the Ancient Greek word κρύσταλλος (krustallos), meaning both "ice" and "rock crystal",[3] from κρύος (kruos), "icy cold, frost".[4][5]
Examples of large crystals include
Despite the name, lead crystal, crystal glass, and related products are not crystals, but rather types of glass, i.e. amorphous solids.
Crystals, or crystalline solids, are often used in
Crystal structure (microscopic)
The scientific definition of a "crystal" is based on the microscopic arrangement of atoms inside it, called the crystal structure. A crystal is a solid where the atoms form a periodic arrangement. (Quasicrystals are an exception, see below).
Not all solids are crystals. For example, when liquid water starts freezing, the phase change begins with small ice crystals that grow until they fuse, forming a
A crystal structure (an arrangement of atoms in a crystal) is characterized by its unit cell, a small imaginary box containing one or more atoms in a specific spatial arrangement. The unit cells are stacked in three-dimensional space to form the crystal.
The
Crystal faces, shapes and crystallographic forms
Crystals are commonly recognized, macroscopically, by their shape, consisting of flat faces with sharp angles. These shape characteristics are not necessary for a crystal—a crystal is scientifically defined by its microscopic atomic arrangement, not its macroscopic shape—but the characteristic macroscopic shape is often present and easy to see.
The flat faces (also called
One of the oldest techniques in the science of crystallography consists of measuring the three-dimensional orientations of the faces of a crystal, and using them to infer the underlying crystal symmetry.
A crystal's crystallographic forms are sets of possible faces of the crystal that are related by one of the symmetries of the crystal. For example, crystals of
Forms may be closed, meaning that the form can completely enclose a volume of space, or open, meaning that it cannot. The cubic and octahedral forms are examples of closed forms. All the forms of the isometric system are closed, while all the forms of the monoclinic and triclinic crystal systems are open. A crystal's faces may all belong to the same closed form, or they may be a combination of multiple open or closed forms.[11]
A crystal's habit is its visible external shape. This is determined by the crystal structure (which restricts the possible facet orientations), the specific crystal chemistry and bonding (which may favor some facet types over others), and the conditions under which the crystal formed.
Occurrence in nature
Rocks
By volume and weight, the largest concentrations of crystals in the Earth are part of its solid bedrock. Crystals found in rocks typically range in size from a fraction of a millimetre to several centimetres across, although exceptionally large crystals are occasionally found. As of 1999[update], the world's largest known naturally occurring crystal is a crystal of beryl from Malakialina, Madagascar, 18 m (59 ft) long and 3.5 m (11 ft) in diameter, and weighing 380,000 kg (840,000 lb).[12]
Some crystals have formed by
Other rock crystals have formed out of precipitation from fluids, commonly water, to form
Ice
Water-based
Organigenic crystals
Many living
Polymorphism and allotropy
The same group of atoms can often solidify in many different ways.
In addition, the same atoms may be able to form noncrystalline
For pure chemical elements, polymorphism is known as allotropy. For example, diamond and graphite are two crystalline forms of carbon, while amorphous carbon is a noncrystalline form. Polymorphs, despite having the same atoms, may have very different properties. For example, diamond is the hardest substance known, while graphite is so soft that it is used as a lubricant. Chocolate can form six different types of crystals, but only one has the suitable hardness and melting point for candy bars and confections. Polymorphism in steel is responsible for its ability to be heat treated, giving it a wide range of properties.
Polyamorphism is a similar phenomenon where the same atoms can exist in more than one amorphous solid form.
Crystallization
Crystallization is the process of forming a crystalline structure from a fluid or from materials dissolved in a fluid. (More rarely, crystals may be deposited directly from gas; see: epitaxy and frost.)
Crystallization is a complex and extensively-studied field, because depending on the conditions, a single fluid can solidify into many different possible forms. It can form a
Specific industrial techniques to produce large single crystals (called
Large single crystals can be created by geological processes. For example,
Crystals can also be formed by biological processes, see above. Conversely, some organisms have special techniques to prevent crystallization from occurring, such as antifreeze proteins.
Defects, impurities, and twinning
An ideal crystal has every atom in a perfect, exactly repeating pattern.[19] However, in reality, most crystalline materials have a variety of crystallographic defects, places where the crystal's pattern is interrupted. The types and structures of these defects may have a profound effect on the properties of the materials.
A few examples of crystallographic defects include vacancy defects (an empty space where an atom should fit), interstitial defects (an extra atom squeezed in where it does not fit), and dislocations (see figure at right). Dislocations are especially important in materials science, because they help determine the mechanical strength of materials.
Another common type of crystallographic defect is an
In semiconductors, a special type of impurity, called a dopant, drastically changes the crystal's electrical properties. Semiconductor devices, such as transistors, are made possible largely by putting different semiconductor dopants into different places, in specific patterns.
Twinning is a phenomenon somewhere between a crystallographic defect and a grain boundary. Like a grain boundary, a twin boundary has different crystal orientations on its two sides. But unlike a grain boundary, the orientations are not random, but related in a specific, mirror-image way.
Mosaicity is a spread of crystal plane orientations. A mosaic crystal consists of smaller crystalline units that are somewhat misaligned with respect to each other.
Chemical bonds
In general, solids can be held together by various types of
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.[21]
Weak van der Waals forces also help hold together certain crystals, such as crystalline molecular solids, as well as the interlayer bonding in graphite. Substances such as fats, lipids 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.[22]Polymer materials generally will form crystalline regions, but the lengths of the molecules usually prevent complete crystallization—and sometimes polymers are completely amorphous.
Quasicrystals
A
Quasicrystals are most famous for their ability to show five-fold symmetry, which is impossible for an ordinary periodic crystal (see crystallographic restriction theorem).
The International Union of Crystallography has redefined the term "crystal" to include both ordinary periodic crystals and quasicrystals ("any solid having an essentially discrete diffraction diagram"[23]).
Quasicrystals, first discovered in 1982, are quite rare in practice. Only about 100 solids are known to form quasicrystals, compared to about 400,000 periodic crystals known in 2004.[24] The 2011 Nobel Prize in Chemistry was awarded to Dan Shechtman for the discovery of quasicrystals.[25]
Special properties from anisotropy
Crystals can have certain special electrical, optical, and mechanical properties that
Not all crystals have all of these properties. Conversely, these properties are not quite exclusive to crystals. They can appear in
.Crystallography
Image gallery
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Insulin crystals grown in earth orbit. The low gravity allows crystals to be grown with minimal defects.
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Hoar frost: A type of ice crystal (picture taken from a distance of about 5 cm).
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Gallium, a metal that easily forms large crystals.
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An apatite crystal sits front and center on cherry-red rhodochroite rhombs, purple fluorite cubes, quartz and a dusting of brass-yellow pyrite cubes.
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A specimen consisting of a bornite-coated chalcopyrite crystal nestled in a bed of clear quartz crystals and lustrous pyrite crystals. The bornite-coated crystal is up to 1.5 cm across.
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Crystallized sugar. Crystals on the right were grown from a sugar cube, while the left from a single seed crystal taken from the right. Red dye was added to the solution when growing the larger crystal, but, insoluble with the solid sugar, all but small traces were forced to precipitate out as it grew.
See also
References
- ^ Stephen Lower. "Chem1 online textbook—States of matter". Retrieved 2016-09-19.
- ^ Ashcroft and Mermin (1976). Solid State Physics.
- Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
- ^ κρύος, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus Digital Library
- ^ "crys·tal". The American Heritage Dictionary of the English Language. Retrieved 2023-06-17.
- ISBN 978-0-313-35507-3
- About.com. Archived from the originalon 15 November 2016. Retrieved 14 November 2016.
- ^ "The Magic of Crystals and Gemstones". WitchesLore. 14 December 2011. Retrieved 14 November 2016.
- S2CID 146060934
- ^ The surface science of metal oxides, by Victor E. Henrich, P. A. Cox, page 28, google books link
- ISBN 0442276249.
- ^ G. Cressey and I. F. Mercer, (1999) Crystals, London, Natural History Museum, page 58
- ^ public domain: Flett, John Smith (1911). "Petrology". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 21 (11th ed.). Cambridge University Press. One or more of the preceding sentences incorporates text from a publication now in the
- ISBN 904812641X, 9789048126415
- ISBN 9781627887335.
- ISBN 9781351416238.
- ^ Nucleation of Water: From Fundamental Science to Atmospheric and Additional Applications by Ari Laaksonen, Jussi Malila -- Elsevier 2022 Page 239--240
- ^ Shea, Neil (November 2008). "Cave of Crystal Giants". National Geographic Magazine. Archived from the original on Dec 19, 2017.
- ^ Britain), Science Research Council (Great (1972). Report of the Council. H.M. Stationery Office.
- ^ Encyclopedia of the Solar System by Tilman Spohn, Doris Breuer, Torrence V. Johnson -- Elsevier 2014 Page 632
- ^ Angelo State University: Formulas and Nomenclature of Ionic and Covalent Compounds
- ^ Science for Conservators, Volume 3: Adhesives and Coatings by Museum and Galleries Commission -- Museum and Galleries Commission 2005 Page 57
- PMC 1826680.
- .
- ^ "The Nobel Prize in Chemistry 2011". Nobelprize.org. Retrieved 2011-12-29.
Further reading
- Howard, J. Michael; Darcy Howard (Illustrator) (1998). "Introduction to Crystallography and Mineral Crystal Systems". Bob's Rock Shop. Archived from the original on 2006-08-26. Retrieved 2008-04-20.
- Krassmann, Thomas (2005–2008). "The Giant Crystal Project". Krassmann. Archived from the original on 2008-04-26. Retrieved 2008-04-20.
- "Teaching Pamphlets". Commission on Crystallographic Teaching. 2007. Archived from the original on 2008-04-17. Retrieved 2008-04-20.
- "Crystal Lattice Structures:Index by Space Group". 2004. Retrieved 2016-12-03.
- "Crystallography". Spanish National Research Council, Department of Crystallography. 2010. Retrieved 2010-01-08.