Despite the fact that many people have a rough idea of what it is, some cannot define the concept of "mineral". The classification of minerals includes a large number of a wide variety of elements, each of which has found application in a particular field of activity due to its advantages and features. Therefore, it is important to know what properties they have and how they can be used.
Minerals are products of artificial or natural chemical reactions that occur both inside the earth's crust and on its surface, and are chemically and physically homogeneous.
Classification
Today, more than 4,000 different rocks are known, which are included in the category of "mineral". The classification of minerals is carried out according to the following criteria:
- genetic (depending on origin);
- practical (raw materials, ore, precious stones, fuel, etc.);
- chemical.
Chemical
Currently the mostThe classification of minerals according to their chemical composition, which is used by modern mineralogists and geologists, is widespread. It is based on the nature of the compounds, the types of chemical bonds between the various structures of the elements, the types of packaging, and many other features that a mineral can have. The classification of minerals of this kind provides for their division into five types, each of which is characterized by the predominance of a certain nature of the relationship between certain structural units.
Types:
- native elements;
- sulfides;
- oxides and hydroxides;
- s alts of oxygen acids;
- halides.
Further, according to the nature of anions, they are divided into several classes (each type has its own division), within which they are already divided into subclasses, from which one can distinguish: framework, chain, island, coordination and layered mineral. The classification of minerals that are similar in composition and have a similar structure provides for their association into various groups.
Characterization of types of minerals
- Native elements. This includes native metalloids and metals such as iron, platinum or gold, as well as non-metals such as diamond, sulfur and graphite.
- Sulfites, as well as their various analogues. The chemical classification of minerals includes hydrosulphuric acid s alts such as pyrite, galena and others in this group.
- Oxides, hydroxides and their other analogues, which arecombination of metal with oxygen. Magnetite, chromite, hematite, goethite are the main representatives of this category, which are distinguished by the chemical classification of minerals.
- S alts of oxygen acids.
- Halides.
It is also worth noting that in the group "s alts of oxygen acids" there is also a classification of minerals by class:
- carbonates;
- sulfates;
- tungstates and molybdates;
- phosphates;
- silicates.
There are also rock-forming minerals, divided into three groups:
- magmatic;
- sedimentary;
- metamorphic.
By origin
The classification of minerals by origin includes three main groups:
- Endogenous. Such processes of mineral formation in the predominant majority of cases involve the intrusion into the earth's crust and subsequent solidification of underground hot alloys, which are commonly called magmas. At the same time, the formation of minerals itself is carried out in three steps: magmatic, pegmatite and postmagmatic.
- Exogenous. In this case, the formation of minerals is carried out under completely different conditions compared to the endogenous one. Exogenous mineral formation involves the chemical and physical decomposition of substances and the simultaneous formation of neoplasms that are resistant to another environment. Crystals are formed as a result of weathering of endogenous minerals.
- Metamorphic. Regardless of the ways in which rocks were formed, their strength or stability, theywill always change under the influence of certain conditions. Rocks that are formed due to changes in the properties or composition of the original samples are commonly called metamorphic.
According to Fersman and Bauer
The classification of minerals according to Fersman and Bauer includes several rocks, intended mainly for the manufacture of various products. Includes:
- gems;
- colored stones;
- organogenic stones.
Physical properties
The classification of minerals and rocks by origin and composition includes many names, and each element has unique physical properties. Depending on these parameters, the value of a particular breed is determined, as well as the possibility of its use in various fields of human activity.
Hardness
This characteristic represents the resistance of a certain solid to the scratching effect of another. Thus, if the mineral in question is softer than the one that is scratched on its surface, marks will remain on it.
The principles of classification of minerals by hardness are based on the use of the Mohs scale, which is represented by specially selected rocks, each of which is capable of scratching previous names with its sharp end. It includes a list of ten items, which begins with talc and gypsum, and ends, as many people know, with diamond - the hardestsubstance.
Initially, it is customary to carry out the rock on glass. If a scratch remains on it, then in this case the classification of minerals by hardness already provides for assigning more than the 5th class to it. After that, the hardness is already specified on the Mohs scale. Accordingly, if a scratch remains on the glass, then in this case a sample is taken from the 6th class (feldspar), after which they try to draw it on the desired mineral. Thus, if, for example, feldspar left a scratch on the sample, but apatite, which is at number 5, did not, it is assigned a class of 5.5.
Do not forget that depending on the value of the crystallographic direction, some minerals may vary in hardness. For example, in disthene, on the cleavage plane, the hardness along the long axis of the crystal has a value of 4, while across the same plane it increases to 6. Very hard minerals can only be found in the group with non-metallic luster.
Shine
The formation of brilliance in minerals is carried out due to the reflection of light rays from their surface. In any manual on minerals, the classification provides for the division into two large groups:
- metallic;
- with non-metallic luster.
The first are those rocks that give a black line and are opaque even in fairly thin fragments. These include magnetite, graphite and coal. Minerals with non-metallic luster and a color streak are also considered here as an exception. It's about goldwith a greenish streak, copper with a peculiar red streak, silver with a silvery white streak, and a number of others.
Metallic in nature is similar to the brilliance of fresh fracture of various metals, and can be seen quite well on the fresh surface of the sample, even when rock-forming minerals are considered. The gloss classification also includes opaque samples, which are heavier than the first category.
Metal luster is characteristic of minerals, which are ore of various metals.
Color
It is worth noting that color is a constant feature only for some minerals. Thus, malachite always remains green, gold does not lose its golden yellow color, etc., while for many others it is unstable. To determine the color, you must first get a fresh chip.
Special attention should be paid to the fact that the classification of the properties of minerals also provides for such a concept as the color of the line (ground powder), which often does not differ from the standard. But at the same time, there are also breeds in which the color of the powder is significantly different from their own. For example, they include calcite, which can be yellow, white, blue, blue, and many other variations, but the powder will remain white anyway.
Powder, or trait of a mineral, is obtained on porcelain, which should not be covered with any glaze andamong professionals, it is simply called "biscuit". A line with the determined mineral is drawn along its surface, after which it is slightly smeared with a finger. We should not forget that hard, as well as very hard minerals do not leave behind any trace due to the fact that they will simply scratch this “biscuit”, so you first need to scrape off a certain part from them onto white paper, and then rub it to the desired state.
Cleavage
This concept implies the property of a mineral to split or split in a certain direction, leaving a shiny smooth surface. It is worth noting the fact that Erasmus Bartholin, who discovered this property, sent the results of the research to a fairly authoritative commission, including such famous scientists as Boyle, Hooke, Newton and many others, but they recognized the discovered phenomena as random, and the laws invalid, although literally a century later it turned out that all the results were correct.
Thus, there are five main gradations of cleavage:
- very perfect - the mineral can be easily split into small plates;
- perfect - with any hammer blows, the sample will split into fragments, which are limited by cleavage planes;
- clear or medium - when trying to split the mineral, fragments are formed, which are limited not only by cleavage planes, but also by uneven surfaces in random directions;
- imperfect - found with certaincomplexities;
- very imperfect - almost no cleavage.
Certain minerals have several cleavage directions at once, which often becomes their main diagnostic feature.
Kink
This concept means the surface of the split, which did not pass along the cleavage in the mineral. To date, it is customary to distinguish between the main five types of fractures:
- smooth - there are no noticeable curves on the surface, but it is not mirror-smooth, as is the case with cleavage;
- stepped - typical for crystals with more or less clear and perfect cleavage;
- uneven - manifested, for example, in apatite, as well as a number of other minerals that have imperfect cleavage;
- splintered - characteristic of fibrous minerals and is somewhat similar to breaking wood across the grain;
- conchoidal - similar in shape to a shell;
Other properties
Quite a large number of minerals have such a diagnostic or distinguishing feature as magnetism. To determine it, it is customary to use a standard compass or a special magnetized knife. Testing in this case is carried out as follows: a small piece or a small amount of powder of the test material is taken, after which it is touched with a magnetized knife or horseshoe. If, after this procedure, the mineral particles begin to attract, thisindicates the presence of a certain magnetism. When using a compass, it is placed on some flat surface, after which they wait for the arrow to align and bring the mineral to it, without touching the device itself. If the arrow starts to move, this indicates that it is magnetic.
Certain minerals that contain carbonic s alts, when exposed to hydrochloric acid, begin to release carbon dioxide, which manifests itself in the form of bubbles, which is why many people call this "boiling". Among these minerals stand out: malachite, calcite, chalk, marble and limestone.
Also, some substances can be well dissolved in water. This ability of minerals is easy to determine by taste, and in particular, this applies to rock s alt, as well as potassium s alts and others.
If it is required to conduct studies of minerals for fusibility and combustion, then you must first chip off a small piece from the sample, and then use tweezers to bring it directly into the flame from a gas burner, spirit lamp or candle.
Forms of their presence in nature
In the vast majority of cases in nature, various minerals occur in the form of intergrowths or single crystals, and can also be shown in the form of clusters. The latter consist of a large number of grains having an internal crystalline structure. Thus, there are three main groups that have a characteristic appearance:
- isometric, equally developed in all three directions;
- elongated, having more elongated shapes in one of the directions;
- elongated in two directions while keeping the third short.
It is worth noting that some minerals can form naturally intergrown crystals, which are then called twins, tees and other names. Such patterns are often the result of intergrowth or intergrowth of crystals.
Views
Do not confuse regular intergrowths and irregular aggregates of crystals, for example, with "brushes" or druses that grow on the walls of caves and various cavities in rocks. Druses are intergrowths formed from several more or less regular crystals and at the same time growing at one end to some kind of rock. Their formation requires an open cavity, which allows for the free growth of minerals.
Among other things, many crystalline minerals are characterized by rather complex irregular shapes, which leads to the formation of dendrites, sinter forms and others. The formation of dendrites is due to the too rapid crystallization of minerals located in thin cracks and pores, and the rocks in this case begin to resemble rather bizarre plant branches.
Often there are situations when minerals almost completely fill a small empty space, which leads to the formation of secretions. They use a concentric structure, andthe mineral substance fills it to the center from the periphery. Sufficiently large secretions, which have empty space inside, are commonly called geodes, while small formations are called tonsils.
Nodules are concretions of irregular round or spherical shape, the formation of which occurs due to the active deposition of mineral substances around a certain center. Quite often, they are characterized by a radially radiant internal structure, and unlike secretions, growth is carried out, on the contrary, towards the periphery from the center.
