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Crystal or crystalline solid is a solid, the elements of which, such as atoms, molecules or ions are arranged in a highly ordered microscopic structure, forming a lattice that extends in all directions. In addition, the macroscopic single crystals are usually distinguished by the geometrical shape, consisting of a flat surface with the specific characteristic direction. The scientific study of crystals and crystal formation is known as crystallography. The process of formation of the crystals through the mechanisms of crystal growth is called crystallization or solidification. The word crystal is derived from the ancient Greek word (krustallos), which means both “ice” and “Rock crystal” from (kruos) “ice cold”. Examples include large crystal snowflakes, diamons and salt. Most of the inorganic solids crystals but poly crystals, ie a lot of microscopic crystals fused together into a single solid. Examples poly crystals include most metals, stones, ceramics and ice. The third category of solids, amorphous solids where the atoms are not periodic structure whatsoever. Examples of amorphous solids are glass, wax, and many plastics. Crystal structure (microscopic) The scientific definition of “crystal” is based on the microscopic arrangement of atoms within it called the crystal structure. A crystal is a solid in which the atoms form a periodic arrangement. (Quasicrystals are an exception, see below.) Not all the solid crystals. For example, when liquid water starts freezing, phase change begins with small ice crystals that grow until they fuse, forming a poly crystalline structure. The final block of ice, each of the small crystals is a true crystal with a periodic arrangement of atoms, but the entire poly crystalline no periodic arrangement of atoms, because a periodic pattern is divided at the grain boundaries. Most of macroscopic inorganic solids are poly crystalline, including almost all metals, ceramics, ice, rock, etc. The solids which are neither crystalline nor poly crystalline, such as glass, are known as amorphous solids, also known as glassy, vitreous or noncrystalline. They do not have regular order, even microscopic. There are distinct differences between crystalline solid and an amorphous solid: in particular, the process of shaping glass does not release the latent heat of fusion, but does form a crystal. The crystal structure (the arrangement of atoms in the crystal) is characterized by a cell, a small imaginary box containing one or more atoms with a particular spatial arrangement. Cell units are stacked in a three dimensional space to form a crystal. The symmetry of the crystal is limited by the requirement that the unit cell stack completely without gaps. There are 219 possible crystal symmetries, called crystallographic space groups. They are classified into seven crystal systems, such as cubic crystal system (where crystals cube or rectangular box like halite shown on the right) or a hexagonal crystal system (which may be crystals of hexagons, such as ordinary tap water and ice). Crystal faces and forms are, by their form commonly known, consists of a flat surface with sharp angles. These forms of properties not required for crystal scientifically identified by microscopic atomic organization, not its macroscopic form but characteristic macroscopic form is often present and easy to see. Euhedral crystals are those with obvious, well-shaped, flat faces. Cathedral crystals do not, usually because crystal is one grain in poly crystalline solid. The flat surface (also called facets) with euhedral crystal is oriented in a certain way relative to the basic atomic arrangement of the crystal: They are relatively low plane index Miller. This occurs because some surface orientation more stable than the other. As the crystal grows, new atoms can attach rougher and less stable parts of the area, but less trouble on flat, stable surface. Therefore, areas grow larger and smoother, until the entire crystal surface consists of flat surfaces. (See diagrams at right.) One of the oldest techniques in the science of crystallography is the measurement of three-dimensional orientation of the crystal faces, and apply them to the conclusion that the basis of crystal symmetry. The habit of a crystal is a visible feature. This is determined by the crystal structure, special crystal chemistry and bonding (which may be imposed for certain types of side over the other), and the conditions under which the crystal formed. Occurrence in nature RocksDepending on the volume and weight, the maximum concentration of crystals in the ground they are part of the Earth's solid rock. Some crystals are formed by igneous and metamorphic processes, whereby the origin of large masses of crystalline rock. The vast majority of igneous rock formed from molten magma and the degree of crystallization depends primarily on the conditions under which harden. Such rocks as granite, which have cooled very slowly and under great pressures, which are fully crystallized; but that many kinds of lava flows on the surface and very rapidly cooled down, and in this latter group, the small amount of amorphous or glassy material joint. Other crystalline rocks, metamorphic rocks, such as marbles, mica schists and quartzites, crystallizes. This means that in the first frag mental rocks such as limestone, slate and sandstone and have never been in a molten state, either in whole solution, but the temperature and pressure conditions of high metamorphism have acted on them by erasing their original structures, and inducing re crystallization in solid state. Other Rock crystals are formed from the precipitation of liquid, usually water, to form druses or quartz veins. The evaporates such as halite, gypsum and some limestones have been deposited from an aqueous solution mainly due to evaporation in dry climates. IceWater-based ice in the form of snow, ice and glaciers is very common manifestation of crystalline or poly crystalline materials on Earth. A single snowflake is usually a single crystal, while the poly crystalline ice cube. Organigenic crystalsMany living organisms are capable of producing the crystal, for example calcite and aragonite, in the case of most of the mollusk, or hydroxyl in the case of vertebrates. Polymorphic and AllotropeThe same group of atoms, often solidify in various ways. Polymorphic is the ability of a solid exists in more than one crystal form. For example, ice water is usually found in the form of hexagonal ice Ih, but may also exist as the cubic Ice Ic, the rhombohedral ice II, and many other forms. Different poly morphs usually called different phases. In addition, the same carbon can form Noncrystalline phase. For example, it may also lead to an amorphous form of ice, while the SiO2 formed as silica (amorphous silica) and quartz (crystal). Similarly, if the substance can form crystals can also be obtained poly crystals. For pure chemical elements, polymorphic is known as Allotrope. For example, diamond and graphite are two crystalline forms of carbon, while the amorphous carbon is a form of noncrystalline. Polymorphs, though they have the same atoms, may be wildly different characteristics. For example, diamon is the hardest substance known, while graphite is so soft that it is used as a lubricant. Polyamorphism is similar to the phenomenon in which may be the same atoms exist in more than one of the amorphous solid form. CrystallizationCrystallization is a method for the formation of the crystalline structure from a liquid or a material dissolved in the liquid. (More rarely, the crystals are deposited directly from the gas; see thin-film deposition and epitaph.) Crystallization of the complex and large-scale researched field, since it is dependent on the conditions, may be a single fluid solidifies in the various possible forms. This can form a crystal, perhaps with various possible stages, stoichiometry, impurities, defects and habits. You can poly crystalline form, with various options for the size, arrangement, orientation, and phase of its grain. The final form of the solid to determine the conditions under which the curing fluid, such as the chemistry of the liquid, ambient pressure, temperature, and the speed with which all of these parameters vary. Special industrial techniques for producing large single crystals (called boules) involves the process of Czochralski and Bridgman technique. They may be used for other less exotic methods of crystallization, depending on the physical properties of the material, including the hydro thermal synthesis, sublimation or merely solvent based crystallization. Large single crystals can be caused by geological processes. For example, selenite crystals that exceed 10 meters found in the cave Crystals in Naica, Mexico. For more details about the geological formation of crystals, you see above. The crystals can be formed as the biological processes, see above. Conversely, some organisms have specific techniques to prevent crystallization from occurring, for example, anti-freeze protein. Errors impurities and twinning Perfect crystal each atom in perfect, exactly repeating the pattern. But in reality, most crystalline materials have a variety of crystallographic defects, the places where the crystal pattern is interrupted. The types and structures of these defects can have a major impact on the properties of materials. Some examples of crystallographic defects including defects of vacancies, interstitial defect and dislocations. Dislocations are especially important in materials science because they help to determine the mechanical strength of the materials. Another common type of crystallographic defects is contamination, which means that it is present in the crystal \'wrong\' type of atom. For example, a perfect crystal diamond containing only carbon atoms, but a true crystal might contain some boron atoms as well. These boron impurities change the color of a diamon is slightly blue. It is also the only difference between the ruby and sapphire is the type of impurities present in the alumina crystal. In semiconductors, a specific type of impurity called do pant drastically alter the electrical properties of the crystal. Semiconductor devices such as transistors are made possible mainly by the introduction of various semiconductor do pants in different places, in some samples. Twinning is a phenomenon somewhere between crystallographic error and grain boundaries. As grain boundaries, twin boundaries it has different crystal orientations on its two sides. But unlike the grain boundaries, guidelines are not random but are linked in a special, reflective way. Mosaicity the expansion of the crystal plane orientation. Mosaic crystal to be composed of smaller crystalline units, which are slightly offset with respect to each other. Chemical bonds Crystal structures are found in all types of materials, all kinds of chemical bonds. There are almost all metals in the poly crystalline state; amorphous or single-crystal metals must be produced synthetically, often with great difficulty. Ionically bonded crystals form upon solidification of salt, either from the molten liquid, or crystallization from solution. Covalently linked crystals are also very common, important examples being diamon, silica and graphite. Polymer materials are generally formed of crystalline regions, but the length of the molecules normally prevents complete crystallization. Weak van der Waals forces can also play a role in a crystal structure; For example, this type of bonding loosely held together by hexagonal-patterned sheets of graphite. They have many attributes in common with the base of the crystals, as shown in a discrete pattern in the X-ray diffraction, and the ability to form a shape with a flat, smooth surface. Quasicrystals are best known for their ability to show a five-fold symmetry, which is impossible for an ordinary periodic crystal. The International Association of Crystallography is newly termed “crystal” that both ordinary regular crystals and quasi crystals. Quasicrystals, first discovered in 1982, they are very rare in practice. Only about 100 solids are known to form quasi crystals, compared with about 400 system.000 regular crystals measured so far.2011 Nobel Prize in Chemistry was awarded Dan Shechtman for his discovery of quasi crystals. Special features of the anisotropy Crystals may have some special electrical, optical and mechanical properties to glass and poly crystals usually can not. These properties are related to the anisotropy of the crystal, ie the lack of rotational symmetry in their atomic arrangements. One such feature is the piezoelectric effect, which can be a voltage on the crystal shrinks or expands. Another reason is birefringence, which appears in a double image when viewed through the crystal. In addition, various properties of the crystal, including electrical conductivity, electric permittivity and Young's modulus are different in different directions in the crystal. For example, a graphite crystal composite from a stack of sheets, and even though each individual sheet mechanically very strong, the leaves are rather loosely connected to each other. Therefore, the mechanical strength of the material varies considerably depending on the load direction. Not all crystals have all these qualities. In contrast, these properties are not entirely exclusive crystals. These can occur in glasses or poly crystals which were an isotropic with treatment or stress, for example, stress-induced birefringence. Crystallography is the science of measuring the crystal structure of crystal. One widespread crystallography technique is X-ray diffraction. A large number of the known crystal structures are stored in the crystallographic database.