Mineralogy. Physical properties of minerals.

Physical properties of minerals have major practical value (a radio-activity, a luminiscence, magnetic, hardness, optical properties, etc.) and are very important for their diagnostics. They depend on an elemental composition and type of crystalline structure. For example, radioactive properties of minerals depend on an elemental composition - presence radioactive of elements, the cleavage of minerals depends on features of their crystalline structure, density - from an elemental composition and from type of crystalline structure. Physical properties can represent a scalar value (are independent of a direction), for example density or to be the vector (depending on a direction), for example hardness, a cleavage, optical properties.

Density. Densities of minerals (in g/sm3) fluctuate from quantities, about equal unities, to 23.0 (platiniridium). The overwhelming mass of minerals has density from 2.5 to 3.5, that causes the density of earth crust equal approximately 2.

Minerals on density can be parted on three groups: lungs (density to 3.0), averages (density from 3.0 to 4) and heavy (density more than 4).

Some minerals are easily learnt on major density (барит4.6, a cerussite 6.5). As a rule, the minerals containing heavy metals, have major density. Native devices - gold, argentum, minerals of group of platinum have the greatest density. In crystals of the same composition the density is spotted by character of packing of atoms in an individual structural mesh.

For the minerals representing isomorphic rows, magnification (or reduction) to density is proportional to elemental composition change.

Mechanical properties of minerals discover at mechanical activity on them: at squeezing, tension and shock. The same as also optical properties, they are various in different directions and are related to anisotropy of crystals. To number of the major mechanical properties carry a cleavage and hardness.

Cleavage - ability of crystals to break up on certain crystallographic planes with formation of brilliant surfaces. The cleavage can be shown in one, two, three, four and six crystallographic directions.

Why in one directions crystals break up on a cleavage, and in others are not present? The cleavage parent consists in a cohesive force between crystal particles, and last depends on distance between particles and from quantity of the ionic charges interreacting among themselves. Cleavage planes should be parallel flat nets of a spatial lattice with the greatest interplanar distances.

For a cleavage estimation there is a following scale:

1. The cleavage rather made - a crystal is pricked on the most thin plates with a smooth surface (mica, gypsum).
2. The cleavage made - a crystal in any place is pricked on determinate directions, forming equal surfaces; the wrong break is gained extremely seldom (calcite, a halite, a galena).
3. Cleavage medial - at splitting are formed both equal cleavage surfaces, and rough surfaces of a break (field spars, a hornblende).
4. Cleavage imperfect - equal cleavage surfaces are rare, at a break the wrong break (beryl, apatite) is mostly formed.
5. The cleavage rather imperfect - practically is not present a cleavage, crystals have rough surfaces of a break at splitting (quartz, cassiterite).

In various directions the crystal cleavage can be identical or different in a perfection degree.

Hardness. Hardness of a crystal is understood as its resistance to mechanical action of stronger body.

There are some methods of definition of hardness. In mineralogical practice the Mohs scale is accepted. It is necessary to score a scale relativity: if the talcum has hardness 1, and gypsum hardness 2 it does not mean, that gypsum in 2 times is more solid than a talcum. Too most it is possible to tell and concerning other minerals-etalons. Their hardness is conventional, and at definition by other methods other values are gained.

The same as also the cleavage, hardness of crystals discovers anisotropy. Diamond crystals have the greatest cleavage on octahedron facets, smaller on rhombic dodecahedron facets, still smaller on cube facets.

Optical properties. In natural light oscillations of electrical and magnetic vectors are made during each moment in various directions, always perpendicular to a light wave direction of propagation (i.e. it is perpendicular to a light beam). Such light carries the name not polarised, or simple.

At passage through optically anisotropic medium light becomes polarised. Oscillations of polarised light drive only in one plane driving through a direction of a motion of a light wave.

Light polarisation occurs at passage through all crystals, except for crystals of a cubic syngony; the last in the optical relation are isotropic. The natural light arriving in a crystal, breaks up on two light waves spread with various velocities. Both waves become polarised, and planes of their oscillations are crossly perpendicular. This phenomenon is termed as a two-refractive, or double light a refractive. The two-refractive was open Bartholin in 1669 and further has been studied by H.Gjujgensom.

In crystals of trigonal, tetragonal and hexagonal syngonies there is only one direction on which there is no double refractive light. This direction is termed as an optical axis, it coincides with a symmetry axis of the higher order. Therefore crystals of medial syngonies are termed optically as the uniaxial. In crystals of triclinic, monoclinic and trimetric syngonies there are two directions on which there is no double refractive light; they in the optical relation are biaxial.

In crystals of medial syngonies velocity of distribution of light waves is various. The light wave spread with identical velocity in all directions, is termed ordinary, and spread in various directions with various velocity - unusual. A surface of the first light wave is the ball, and second - an ellipsoid of revolution.

Colour. Minerals can have the most various colours and tones. Colour of minerals depends on their interior structure, from mechanical impurities and mainly from presence of elements-chromophores, i.e. colouring carriers. Many devices-chromophores are known, are that Cr, V, Ti, Mn, Fe, Ni, Co, Cu, U, Mo and some other. These devices can be in a mineral the main things, or can be in the form of impurities.

Blueing - speckled or iridescent colouring of a near-surface stratum. She speaks occurrence of thin superficial films for the change account, for example acidifications, minerals.

Colour of line. The minerals, which hardness it is insignificant, leave line on an unglazed porcelain plate. Colour of line, or colour of a mineral in a powder can will cause a stir from colour of the mineral.

Brilliance. Distinguish minerals with metal and nonmetallic brilliance. Those minerals (it is not dependent on their colouring) which give black line have metal brilliance. Nonmetallic brilliance is characteristic for the minerals giving colour or white line. An exception are only native devices.

Magnetic. This property is characteristic for few minerals. The strongest magnetic properties the magnetite possesses. Minerals possessing the strong polar magnetism, are termed as the ferromagnetic.

Exist still: a luminescence, a pyroelectricity, a radio-activity, etc.