Physical properties of minerals: description, characterization
Scientists have long studied the basic physical properties of minerals. They are held in the school curriculum (usually in geography or chemistry), and at the university. Students are geared especially well in this area in the geological direction, as well as those who have chosen this area for work or as an object of scientific research. Consider the most basic and curious qualities.
Dedicated to optics: show me everything!
Often, the characteristic of the physical properties of minerals begins with the classification of a substance as transparent or not. The term is used to denote the ability to let through a mineral structure a ray beam. Transparency is a characteristic described by levels. The most typical representative of transparent minerals is crystal. Excellent performance are different topaz, spar come from Iceland. From translucent cinnabar is worth mentioning, but the most opaque is most of all - it is graphite, pyrite and many other varieties.Often, the samples represented by large specimens seem to be opaque at first glance, but when examining grain edges, fragments of small thickness, it appears that they have a rather strong ability to transmit light radiation.
Analyzing the classification of minerals, their physical properties, it should be noted that color is traditionally among the most significant parameters. It is this symptom that is investigated first in the diagnosis of the sample. The coloring is associated with both internal features (idiochromatic aspect), and the presence of chromophores in the total mass of the substance. A good example that occurs quite often is the green tint of emerald, due to inclusions of chromium. But tourmaline will sparkle with beautiful shades of pink due to the presence of manganese in its structure.
The color of a number of minerals is due to a heterogeneous structure. This is typical of Morion, some types of quartz. The crystal lattices of such minerals are distinguished by numerous defects, due to which the refraction of light creates interesting colors. Also known are minerals, the color of which is due to mechanical impurities scattered by an extremely thin layer.The official scientific name of this phenomenon is allochromatic color. This effect is due to the color of jasper, aventurine and some other minerals.
Determining the physical properties of a mineral of this type involves identifying the hue of the mineral crushed into a very fine powder. The easiest way to get a mineral line is to hold a porcelain plate with a sample intended for research. The object must be matte, glazing is unacceptable. In addition to biscuit, you can use chemical dishes made from porcelain and having a surface with the same qualities.
If we compare the color and this physical property of the mineral, we can notice that it is much more permanent. It also happens that the trait has the same shade as the test sample, but there are cases of tangible differences. For example, hematite, at the initial examination, assessed as gray with a steel tint, draws a line of red (ripe cherry). The situation is similar with pyrite, which is tinged with a shade of yellow similar to the color of brass - its feature is black.
The joy of the magpie
If you ask a student, a student “What physical properties of minerals you know,” one of the first to come to mind is brilliance. The characteristic is determined by the degree of refraction. This is a parameter, the calculation of which is based on the difference in the speed parameters of the luminous flux when a crystal passes from the air into the medium. If the parameter varies in the range of 1.3-1.9, the material will shine like glass. A good example is the guarantor, quartz.
Diamond shine is characterized by a quantitative indicator of 1.3-1.9. Diamond itself, as well as rutile, calcite and some other rocks, have this feature. When the characteristic refraction of 2.6-3.0 speak of polymetallic luster. The brightest representatives of such a group of natural substances are hematite, cuprite. Finally, three or more is a parameter that speaks of metallic luster. It is characteristic of pyrite, molybdenite and many other minerals.
This physical property of minerals is one of the basic. It reflects how much the crystal structure is characterized by splits in different directions. This is explained by the structure of the lattice. For example, if we consider calcite, then its cleavage crystals always give rhombohedrons when unfolded, it does not matter what it was initially necessary to work with.Fluorite cube will give a scattering of octahedra. The level of perfection is usually classified according to a special scale.
The greatest indicator (very perfect) is the physical property of the mineral, which reflects the ease of splitting the original sample into sheets of small thickness. In nature, these are mica, chlorite. Perfect - such a cleavage, which, with a strong blow, reveals cleavages on the cleavage, but it is problematic to break the source material in other directions. These are fluorite, calcite.
What else are there?
The description of the physical properties of the cleavage minerals may contain the characteristic “medium level”. This is typical, for example, pyroxene. When working with the sample in all directions, you can achieve a kink. In the study of debris, some planes will be smooth, they tend to shine. These are the cleavage planes. All other edges - uneven, broken.
Analyzing the physical and chemical properties of minerals, one can notice that some materials have a granular structure, and some of the elements are quite diverse in size and shape, due to which the surface is irregular.The exception is crystal facets. For such substances, imperfect cleavage is characteristic, or the indicator is absent in principle.
In a nutshell, the physical property of minerals, described by the term “split cracks,” is inherently the opposite of cleavage. When examining a specimen, one can notice coarse, often located across the mineral elongation of the crack. Usually they are close to flat, but not perfect enough to be described as such.
Describing briefly the physical properties of minerals, this feature is also necessarily mentioned. If the mineral characterizes the cleavage of the imperfect level, it is precisely due to the fracture that the sample can be studied in detail. In some breeds, it is shell-like. This is characteristic of quartz, pyrochlore. Others seem to be splinters. This is more typical of nuggets. Bornite, pyrite are described by finely bent kinks. There are some minerals that have this feature that can be attributed to the group of uneven rocks.
An alternative name for this quality is the ability of a material to resist aggressive external factors that mechanically influence the structure. To understand how hard the mineral is, you need to scratch it with a different pattern.Characteristic features in quantitative form is subject to the Mohs scale. Its essence is ten levels, each of which is able to scratch the previous sample. The reference has been selected (ascending, from the first to the tenth levels): talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, diamond.
As a toolkit in determining the characteristics of the material, copper, steel needles are often used. The first one scratches the surface down to 3.5 level, the second - up to the sixth. A similar parameter (up to six) gives a knife, a little less (up to five) - glass. When examining a soft sample, you can try it on hardness with your own fingernail. The human nail plate is rated at 2.5 on the Mohs scale. Analyzing the physical properties of the amethyst mineral, the hardness will have to be estimated at seven units.
What are you
The study of the characteristics of a particular sample implies an assessment of its fragility. This parameter for the amethyst mentioned above, for example, is rather high — the mineral is fragile. This means that when exposed to a needle or knife, the rock crumbles easily. Sometimes, when a knife is held on a mineral specimen, a smooth trace remains, which differs from the other surface by gloss. This indicates plastic deformation of the structure.
Another interesting feature is malleability. If the sample is hit with a heavy hammer, it will turn into a plate of small thickness. The opposite feature is elasticity, that is, the possibility of restoring the original form when the external load disappears. The classic representatives of minerals with high elasticity are asbestos, mica.
What else to pay attention to?
There are quite a few important features, and there is a dependence on the origin: the physical properties of non-metallic minerals, ore, often differ quite strongly in their performance. It is for this reason that many prefer to begin the study of a particular sample by determining the nature of the material.
Do not neglect the assessment of the specific weight. The most accurate indicators can be obtained by having highly efficient laboratory equipment with minimal error. Various techniques are used. If a rough estimate is sufficient, it is possible to compare a specific mineral with a similar common natural component, whose specific gravity is assessed by the physicists as a reference.
Specific gravity is a characteristic that makes it possible to classify a specific sample in one of three categories. There is a figure of less than three, it is a light mineral, if the value varies in the range from three to five, the specific gravity is characterized as average. More parameters are heavy samples. To the lungs belongs quartz, the representative of the medium is corundum, from heavy gold is worth mentioning.
When and pulls
Analysis of a sample of a mineral involves the study of its magnetic properties. It is known that some are naturally strong ferromagnets capable of attracting small elements made of iron. When experimenting more often use pins, sawdust. The optimal material for the manufacture of these items is iron with a high percentage of nickel, magnetite.
There are paramagnetic minerals that can be attracted if you have an electric magnet or pyrrhotite at your disposal. The latter category is diamagnetic, that is, substances that will repel with a magnet. In nature, the most characteristic representative is bismuth in the form of a nugget.
How to identify?
To assess the magnetic quality of the test sample, suitable laboratory equipment should be organized. It is quite simple.A magnetic needle is taken, the mineral is brought closer to its end and the reaction of the revolving object is monitored.
As it was possible to reveal in the course of numerous experiments, minerals with strong magnetic qualities are a rather narrow list of names. Often, it is the magnetism that is oriented in determining the nature of a particular sample, while neglecting other features. This is true, for example, for magnetite.
Radiation is coming!
One of the features of minerals is radioactivity. Having learned about this fact, a man in the street can be scared for nothing, but scientists have long figured out that this quality is inherent in those minerals present on our planet that include thorium and uranium. True, the radiation power of particles of all categories is usually relatively small. If you pay attention to the experience of the excavation of radioactive rocks, you can learn that in most cases the deposits were characterized by a red or brown border. Often mineral radioactive grains are found in the thickness of spar and quartz. It is not difficult to identify them - small cracks radially radially interspersed in different directions.Examining samples, you can use special photo paper. Natural radiation is strong enough to leave a mark on it.
Learn at the first meeting
Once in the field, geologists often face the challenge of quickly identifying a particular mineral. One of the fairly simple ways to identify characteristic physical qualities is to check for interaction with water. Chlorides, for example, quickly dissolve. If water has no tangible effect on the sample, it can be influenced by alkali, acid.
Detection of the presence of a separate element in the composition of a rock is possible by means of a private chemical reaction. For example, hydrogen chloride allows you to quickly identify carbonates, ammonium - phosphates. A number of minerals change the color of the flame.
What else to pay attention to?
There are such minerals that, when broken, become a source of characteristic odor. The easiest way to recognize this is arsenic, which smells like garlic. Not more difficult to identify and arsenopyrite. There are some types of minerals whose distinctive physical property is a surface that is defined by touch.So you can identify talc - it is fat. A number of compounds are identified by taste. A good example is table salt. Similarly, some other salt mineral samples can be determined.