When looking at crystals and gem products, I want to understand how this mysterious beauty could have appeared, how such amazing works of nature are created. There is a desire to learn more about their properties. Indeed, the special, nowhere in nature repeated structure of crystals allows you to use them everywhere: from jewelry to the latest scientific and technical inventions.
The study of crystalline minerals
The structure and properties of crystals are so multifaceted that a separate science, mineralogy, is engaged in the study and investigation of these phenomena. The famous Russian academician Alexander Evgenievich Fersman was so absorbed and surprised by the variety and limitlessness of the crystal world that he sought to captivate as many minds as possible with this topic. In his book “Entertaining Mineralogy,” he enthusiastically and warmly urged to get acquainted with the secrets of minerals and plunge into the world of gems:
I really want to captivate you. I want you to become interested in mountains and quarries, mines and mines, so that you start collecting mineral collections, so that you want to go with us from the city away, to the river, where there are high rocky shores, to the tops of the mountains or to the rocky shore of the sea, where stone is broken, sand is mined or ore is blown up. Everywhere we find with you what to do: and in dead rocks, sands and stones, we will learn to read some great laws of nature that govern the whole world and on which the whole world is built.
Physics studies crystals, arguing that every really solid body is a crystal. Chemistry investigates the molecular structure of crystals, concluding that any metal has a crystalline structure.
The study of the amazing properties of crystals is of great importance for the development of modern science, technology, the construction industry and many other industries.
Basic laws of crystals
The first thing you pay attention to when looking at a crystal is its ideal multifaceted shape, but it is not the main feature of a mineral or metal.
When breaking the crystal into small fragments, nothing will remain of the ideal form, but any fragment will remain a crystal, as before. A distinctive feature of a crystal is not its appearance, but the characteristic features of its internal structure.
Symmetry
The first thing to remember and note when studying crystals is the phenomenon of symmetry. It is widespread in everyday life. The wings of a butterfly are symmetrical, the imprint of a blot on a sheet of paper bent in half. Snow crystals are symmetrical. The hexagonal snowflake has six planes of symmetry. By bending the pattern along any line depicting the plane of symmetry of the snowflake, you can combine two of its halves with each other.
The axis of symmetry has such a property that by rotating the figure at some known angle around it, it is possible to combine the appropriate parts of the figure. Depending on the size of a suitable angle by which the figure needs to be rotated, axes of the 2nd, 3rd, 4th and 6th order are determined in crystals. Thus, in snowflakes there is a single axis of sixth order symmetry, which is perpendicular to the drawing plane.
The center of symmetry is considered to be such a point in the plane of the figure, at the same distance from which in the opposite direction there are identical structural elements of the figure.
What's inside?
The internal structure of crystals is a peculiar combination of molecules and atoms in the order characteristic only of crystals. How do they recognize the internal structure of particles if they are not visible even through a microscope?
For this, x-rays are used. Using them to shine through crystals, the German physicist M. Laue, the British physicists father and son Bragg, and the Russian professor J. Woolf established the laws according to which the structure and structure of crystals are studied.
Everything turned out to be surprising and unexpected. The very idea of the structure of the molecule turned out to be inapplicable to the crystalline state of matter.
For example, a substance known to everyone as table salt has the chemical composition of a NaCl molecule. But in a crystal, individual chlorine and sodium atoms do not add up to separate molecules, but form a specific configuration, called a spatial or crystalline lattice. The smallest particles of chlorine and sodium have an electrical connection. The crystal lattice of salt is folded as follows. One of the valence electrons of the outer shell of the sodium atom is introduced into the outer shell of the chlorine atom, which is not completely filled due to the absence of the eighth electron in the third shell of chlorine. Thus, in a crystal, each ion of both sodium and chlorine does not belong to one molecule, but to the whole crystal. Due to the fact that the chlorine atom is monovalent, it can attach only one electron to itself. But the structural features of the crystals lead to the fact that the chlorine atom is surrounded by six sodium atoms, and it is impossible to determine which of them will share an electron with chlorine.
It turns out that the chemical molecule of salt and its crystal are not at all the same thing. The whole single crystal is like one giant molecule.
Grill - Model Only
Mistakes should be avoided when the spatial lattice is taken as the actual model of the crystal structure. The lattice is a kind of conditional image of an example of the combination of elementary particles in the structure of crystals. The junction of the lattice in the form of balls clearly depict atoms, and the lines connecting them - this is an approximate image of the bonding forces between them.
In reality, the gaps between the atoms inside the crystal are much smaller. It is a dense packing of its constituent particles. A ball is a symbol of an atom, the use of which allows one to successfully reflect the properties of dense packing. In reality, there is not a simple contact of atoms, but their mutual partial overlapping. In other words, the image of the ball in the structure of the crystal lattice is for illustration purposes the depicted sphere of such a radius that contains the bulk of the electrons of the atom.
Pledge of strength
Between two oppositely charged ions, an electric attractive force arises. It is a binder in the structure of ionic crystals, such as sodium chloride. But if ions are brought very close, their electronic orbits will overlap each other, repulsive forces of the same charged particles will appear. Inside the crystal, the ion distribution is such that the repulsive and attractive forces are in equilibrium, providing crystalline strength. Such a structure is characteristic of ionic crystals.
And in the crystal lattices of diamond and graphite, a combination of atoms takes place with the help of common (collective) electrons. Nearly adjacent atoms have common electrons that rotate around the nucleus of both one and neighboring atoms.
A detailed study of the theory of forces with such connections is rather complicated and lies in the field of quantum mechanics.
Metal Differences
The structure of metal crystals is more complex. Due to the fact that metal atoms easily give away available external electrons, they can freely move throughout the entire volume of the crystal, forming inside it the so-called electron gas. Thanks to such "wandering" electrons, forces are created that ensure the strength of the metal ingot. A study of the structure of real metal crystals shows that, depending on the method of cooling a metal ingot, there may be imperfections in it: surface, point, and linear. The sizes of such defects do not exceed the diameter of several atoms, but they distort the crystal lattice and affect diffusion processes in metals.
Crystal growth
For a more convenient understanding, the growth of crystalline matter can be represented as the erection of a brick structure. If one brick of unfinished masonry is presented as an integral part of the crystal, then we can determine where the crystal will grow. The properties of the crystal energy are such that the one placed on the first brick will experience attraction from one side - from the bottom. When laying on the second - from two sides, and on the third - from three. In the process of crystallization - the transition from a liquid to a solid state - energy (heat of fusion) is released. For the greatest strength of the system, its possible energy should tend to the minimum. Therefore, crystal growth occurs layer by layer. First, a row of the plane will be completed, then the entire plane, and only then the next one begins to be built.
Crystal science
The basic law of crystallography - the science of crystals - suggests that all angles between different planes of crystalline faces are always constant and the same. No matter how distorted the growing crystal, the angles between its faces retain the same value inherent in this species. Regardless of size, shape and number, the faces of one plane of the crystal always intersect at the same predetermined angle. The law of constancy of angles was discovered by M.V. Lomonosov in 1669 and played a large role in the study of the structure of crystals.
Anisotropy
The peculiarity of the process of crystal formation is due to the phenomenon of anisotropy - different physical characteristics depending on the direction of growth. Single crystals in different directions conduct electricity, heat and light differently and have different strengths.
Thus, the same chemical element with the same atoms can form different crystal lattices. For example, carbon can crystallize into diamond and graphite. At the same time, diamond is an example of maximum strength among minerals, and graphite easily leaves its flakes when writing in pencil on paper.
The measurement of the angles between the faces of minerals is of great practical importance for determining their nature.
Basic properties
Having learned the structural features of crystals, we can briefly describe their main properties:
- Anisotropy is the dissimilarity of properties in different directions.
- Homogeneity - the elementary components of crystals, equally located in space, have the same properties.
- Self-cutting ability - any crystal fragment in a medium suitable for its growth will take a multifaceted shape and will be covered with faces corresponding to this type of crystal. It is this property that allows the crystal to maintain its symmetry.
- Constant melting point. The destruction of the spatial lattice of a mineral, that is, the transition of a crystalline substance from a solid to a liquid state, always occurs at the same temperature.
Crystals are solids that have taken the natural shape of a symmetrical polyhedron. The crystal structure, characterized by the formation of a spatial lattice, served as the basis for the development in physics of the theory of the electronic structure of a solid. The study of the properties and structure of minerals is of great practical importance.