Crystallography Crystallography In crystallography, atomic packing factor is the fraction of volume in a crystal structure that is occupied by atoms. It is dimensionless and always less than unity. For practical purposes, the APF of a crystal structure is determined by assuming that atoms are rigid spheres. It is represented mathematically by ...more on Wikipedia about "Atomic packing factor"
Bisectrix (fem. of Lat. bisector, from bi-, "two", secare, "to cut"), in geometry, is the same as bisector, i.e. a point which divides a line, or a line which divides an angle, into two equal parts. In crystallography it denotes the bisector of the angle between the optic axes. ...more on Wikipedia about "Bisectrix"
In physics, Bragg's law is the result of experiments into the diffraction of x-rays off crystal surfaces at certain angles, derived by the English physicists Sir W.H. Bragg and his son Sir W.L. Bragg in 1913. Although simple, Bragg's law confirmed the existence of real particles at the atomic scale, as well as providing a powerful new tool for studying crystals in the form of x-ray diffraction. The Braggs were awarded the Nobel Prize in physics in 1915 for their work in determining crystal structures beginning with NaCl, ZnS, and diamond. ...more on Wikipedia about "Bragg's law"
In geometry and crystallography, a Bravais lattice is an infinite set of points generated by a set of discrete translation operations. A crystal is made up of one or more atoms (the basis) which is repeated at each lattice point. The crystal then looks the same when viewed from any of the lattice points. There are in all 14 possible Bravais lattices that fill three dimensional space. ...more on Wikipedia about "Bravais lattice"
Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: ...more on Wikipedia about "Cleavage (crystal)"
Close-packing of spheres is the arranging of an infinite lattice of spheres so that they take up the greatest possible fraction of an infinite 3-dimensional space. Carl Friedrich Gauss proved that the highest average density that can be achieved by a regular lattice arrangement is . The Kepler conjecture states that this is the highest density that can be achieved by any arrangement of spheres, either regular or irregular. ...more on Wikipedia about "Close-packing"
In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ...more on Wikipedia about "Crystal habit" You've Got Questions. We've Got www.shortopedia.com.
Crystal optics is the branch of optics that describes the behaviour of light in anisotropic media, that is, media (such as crystals) in which light behaves differently depending on which direction the light is propagating. Crystals are often naturally anisotropic, and in some media (such as liquid crystals) it is possible to induce anisotropy by applying e.g. an external electric field. ...more on Wikipedia about "Crystal optics"
In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. A crystal structure is composed of a unit cell, a set of atoms arranged in a particular way; which is periodically repeated in three dimensions on a lattice. The spacing between unit cells in various directions are called its lattice parameters. The symmetry properties of the crystal are embodied in its space group. ...more on Wikipedia about "Crystal structure"
A crystal system is a category of space groups, which characterize symmetry of structures in three dimensions with translational symmetry in three directions, having a discrete symmetry group. A major application is in crystallography, to categorize crystals, but by itself the topic is one of 3D Euclidean geometry. ...more on Wikipedia about "Crystal system"
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals. Crystallographers classify twinned crystals by a number of twin laws. These twin laws are specific to the crystal system. The type of twinning can be a diagnostic tool in mineral identification. ...more on Wikipedia about "Crystal twinning"
Crystallization is a solid-liquid separation technique, or the process of formation of solid crystals from a homogeneous solution. ...more on Wikipedia about "Crystallization processes"
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 interrupted by crystal defects. The various types of defects are enumerated here. ...more on Wikipedia about "Crystallographic defect"
A crystallographic group is a topologically discrete subgroup of the group of isometries of some geometric space (typically, not necessarily a Euclidean space) with a compact fundamental domain. ...more on Wikipedia about "Crystallographic group"
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In crystallography, a crystallographic point group is a set of symmetry operations, like rotations or reflections, that leave a point fixed while moving each atom of the crystal to the position of an atom of the same kind. That is, an infinite crystal would look exactly the same before and after any of the operations in its point group. In the classification of crystals, each point group corresponds to a crystal class. ...more on Wikipedia about "Crystallographic point group"
The crystallographic restriction theorem in its basic form is the observation that the rotational symmetries of a crystal are limited to 2-fold, 3-fold, 4-fold, and 6-fold. This is valid only for true crystals, which have translational symmetry; there are also quasicrystals with other symmetries, such as 5-fold. ...more on Wikipedia about "Crystallographic restriction theorem"
Crystallography (from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write) is the experimental science of determining the arrangement of atoms in solids. In older usage, it is the scientific study of crystals. ...more on Wikipedia about "Crystallography"
In crystallography, the cubic crystal system (or isometric crystal system) is the most symmetric of the 7 crystal systems. The system is composed of the three Bravais lattices whose symmetry group is that of a cube. ...more on Wikipedia about "Cubic (crystal system)"
Dan Shechtman is the Philip Tobias Professor of Materials Science at the Israel Institute of Technology. In 1982, he discovered the Icosahedral Phase which opened the new field of quasiperiodic crystals. ...more on Wikipedia about "Dan Shechtman"
The Debye-Waller factor, also known as the B factor or the temperature factor describes the decrease in scattering intensity (either from x-ray or neutron scattering) due to the thermal motion of the atoms, or due to crystal disorder. The thermal motion, or disorder, in some sense reduces the validity of the Laue diffraction condition which is based on fixed atoms. ...more on Wikipedia about "Debye-Waller factor"
Electron crystallography is a method to determine protein structures using electron diffraction. It is conducted with an electron microscope, usually on proteins (such as membrane proteins), that cannot easily form the large 3-dimensional crystals required for X-ray crystallography. Rather, structures are usually determined from either 2-dimensional crystals (sheets or helices), polyhedrons such as viral capsids, or dispersed individual proteins. Electrons can be used in these situations, whereas X-rays cannot, because electrons interact more strongly with proteins than X-rays do. Thus, X-rays will travel through a thin 2-dimensional crystal without diffracting significantly, whereas electrons can be used to form an image. Conversely, the strong interaction between electrons and proteins makes thick (e.g. 3-dimensional) crystals impervious to electrons, which only penetrate short distances. ...more on Wikipedia about "Electron crystallography"
In geometry, a Euclidean plane isometry is an isometry of the Euclidean plane, or more informally, a way of transforming the plane that preserves geometrical properties such as length. There are four types: translations, rotations, reflections, and glide reflections (see below under classification of Euclidean plane isometries). ...more on Wikipedia about "Euclidean plane isometry"
Euhedral refers to well-formed crystals with sharp, easily-recognized faces. Normally, crystals do not form smooth faces or sharp crystal outlines. Many crystals grow from cooling liquid magma. As magma cools, the crystals grow, and they eventually touch each other, preventing crystal faces form forming properly or at all. ...more on Wikipedia about "Euhedral"
In solid state physics, in particular crystallography, the Ewald construction is a method for reconstructing a crystal structure by examining and interpreting an x-ray diffraction pattern. ...more on Wikipedia about "Ewald construction"
Ewald's sphere is a geometric construct used in X-ray crystallography which neatly demonstrates the relationship between ...more on Wikipedia about "Ewald's sphere"
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