When looking at crystals and gems, one wants 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. After all, the special, nowhere in nature repeating structure of crystals allows them to be used everywhere: from jewelry to the latest scientific and technical inventions.
Study of crystalline minerals
The structure and properties of crystals are so multifaceted that a separate science, mineralogy, is engaged in the study and study of these phenomena. The famous Russian academician Alexander Evgenievich Fersman was so absorbed and surprised by the diversity and infinity of the world of crystals that he tried 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 youcaptivate. I want you to begin to be interested in mountains and quarries, mines and mines, so that you begin to collect collections of minerals, so that you want to go with us from the city further away, to the course of the river, where there are high rocky banks, to the tops of mountains or to the rocky seashore, where stone is broken, sand is mined, or ore is exploding. There, everywhere you and I will find something 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 according to which the whole world is built.
Physics studies crystals, arguing that any really solid body is a crystal. Chemistry investigates the molecular structure of crystals, coming to the conclusion 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 people notice when looking at a crystal is its ideal multifaceted shape, but it is not the main feature of a mineral or metal.
When a crystal is broken into small fragments, nothing will remain of the ideal form, but any fragment, as before, will remain a crystal. A distinctive feature of a crystal is not its appearance, but the characteristic features of its internal structure.
Symmetrical
The first thing to remember and note when studying crystals is the phenomenonsymmetry. It is widespread in everyday life. Butterfly wings are symmetrical, an imprint of a blot on a piece of paper folded in half. Symmetrical snow crystals. The hexagonal snowflake has six planes of symmetry. By bending the picture along any line depicting the plane of symmetry of the snowflake, you can combine its two halves with each other.
The axis of symmetry has such a property that, by rotating a figure by some known angle around it, it is possible to combine suitable parts of the figure with each other. 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 the crystals. Thus, in snowflakes, there is a single axis of symmetry of the sixth order, which is perpendicular to the drawing plane.
The center of symmetry is such a point in the plane of the figure, at the same distance from which in the opposite direction are the same structural elements of the figure.
What's inside?
The internal structure of crystals is a kind of combination of molecules and atoms in an order peculiar only to crystals. How do they know the internal structure of particles if they are not visible even with a microscope?
X-rays are used for this. Using them to translucent crystals, the German physicist M. Laue, the English physicists father and son Bragg, and the Russian professor Yu. Wolf established the laws according to which the structure and structure of crystals are studied.
Everything was surprising and unexpected. Samothe concept of the structure of the molecule turned out to be inapplicable to the crystalline state of matter.
For example, such a well-known substance as table s alt has the chemical composition of the NaCl molecule. But in a crystal, individual atoms of chlorine and sodium do not add up to separate molecules, but form a certain configuration called a spatial or crystal lattice. The smallest particles of chlorine and sodium are electrically bonded. The crystal lattice of s alt is formed 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 entire 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 table s alt and its crystal are not the same thing at all. The whole single crystal is like one giant molecule.
Grille - model only
The error should be avoided when the spatial lattice is taken as a real model of the crystal structure. Lattice - a kind of conditional image of an example of the connection of elementary particles in the structure of crystals. Grid connection points in the form of ballsvisually allow you to depict atoms, and the lines connecting them are an approximate image of the binding forces between them.
In reality, the gaps between atoms inside a crystal are much smaller. It is a dense packing of its constituent particles. A ball is a conventional designation of an atom, the use of which makes it possible to successfully reflect the properties of close packing. In reality, there is not a simple contact of atoms, but their mutual partial overlapping with each other. In other words, the image of a ball in the structure of the crystal lattice is, for clarity, the depicted sphere of such a radius that contains the main part of the atom's electrons.
Pledge of Strength
There is an electric force of attraction between two oppositely charged ions. It is a binder in the structure of ionic crystals such as table s alt. But if you bring the ions very close, then their electron orbits will overlap each other, and repulsive forces of like-charged particles will appear. Inside the crystal, the distribution of ions is such that the repulsive and attractive forces are in balance, providing crystalline strength. This structure is typical for ionic crystals.
And in the crystal lattices of diamond and graphite there is a connection of atoms with the help of common (collective) electrons. Closely spaced atoms have common electrons that revolve around the nucleus of both one and neighboring atoms.
A detailed study of the theory of forces with such bonds is quite difficult 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 donate the available external electrons, they can freely move throughout the entire volume of the crystal, forming the so-called electron gas inside it. Thanks to such "wandering" electrons, forces are created that ensure the strength of the metal ingot. The study of the structure of real metal crystals shows that, depending on the method of cooling a metal ingot, it may contain imperfections: surface, point and linear. The size of such defects does 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 a crystalline substance can be represented as the erection of a brick structure. If one brick of an unfinished masonry is presented as an integral part of a crystal, then it is possible to determine where the crystal will grow. The properties of the energy of the crystal are such that the brick placed on the first brick will experience attraction from one side - from below. 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 a minimum. Therefore, the growth of crystals occurs layer by layer. First, a row of the plane will be completed, then the entire plane, and only then the next one will begin to be built.
Science ofcrystals
The basic law of crystallography - the science of crystals - says that all angles between different planes of crystal faces are always constant and the same. No matter how distorted a growing crystal is, the angles between its faces retain the same value inherent in this type. Regardless of size, shape, and number, the faces of the same crystal plane always intersect at the same predetermined angle. The law of constancy of angles was discovered by M. V. Lomonosov in 1669 and played a major 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 conduct electricity, heat and light differently in different directions and have unequal strength.
Thus, the same chemical element with the same atoms can form different crystal lattices. For example, carbon can crystallize into diamond and into graphite. At the same time, diamond is an example of the maximum strength among minerals, and graphite easily leaves its scales when writing with a pencil on paper.
Measuring the angles between the faces of minerals is of great practical importance for determining their nature.
Basic Features
Having learned the structural features of crystals, we can briefly describe their main properties:
- Anisotropy - uneven properties in different directions.
- Uniformity - elementarythe constituents of crystals, equally spaced, have the same properties.
- The ability to self-cutting - any fragment of a crystal in an environment suitable for its growth will take a multifaceted shape and will be covered with faces corresponding to this type of crystals. It is this property that allows the crystal to maintain its symmetry.
- The invariance of the 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 structure of crystals, 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.
