How are minerals classified according to their chemical composition? Minerals and mineralogy
Every person at least once in his life saw minerals - products of natural chemical reactions that took place within the earth's crust millions of years ago. At the same time, not everyone can tell about what a mineral is and why it is needed. Our article will go into detail about the types of mineral deposits, as well as how to use them.
What is a mineral?
Minerals are solid inorganic substances of natural origin. They possess crystal structure, which is their main distinctive feature. Some minerals can be produced artificially. Regardless of the origin, they will have a number of useful properties.
Are there liquid minerals? If we take the usual conditions of life, then yes. This, for example, is natural mercury - a native substance that has hardness only at low temperatures. Scientists also classify some types of ice as minerals. However, water is not included in the group under consideration.
The question of what a mineral is has not been fully resolved to this day. So, a few experts attribute oil, bitumen and asphalt to the group of mineral substances. The validity of such claims is questionable.
Types of minerals
According to Bauer and Fersman, chemists of the late 19th century, all mineral rocks are divided into gems, organogenic stones and non-ferrous substances. Such a classification has such a peculiar appearance due to the deep conviction of pragmatic academicians that all stones and minerals are intended for the manufacture of various products - tools and jewelry.
In order to better understand the question of what minerals are, it is worth bringing the most common scientific classification. According to the structural-chemical principle, minerals are divided into rock-forming - making up the majority rocks, as well as rare, ore and accessory (not more than 5% of the rock).
The native class of minerals includes metals and metalloids. Ore substances form most native group. Accessory minerals are characterized by a special rarity.
Chemical classification
The chemical structure of most minerals is approximately the same. At present, the division of the considered substances into classes is accepted. This results in the following classification:
- silicates. Numerous class, including more than 800 different mineral deposits. Silicates make up the majority of metamorphic and igneous rocks. Some minerals here are distinguished by a common structure and composition. As an example, it is worth highlighting pyroxenes, micas, feldspars, amphiboles, clay materials and much more. The composition of most silicates is referred to as aluminosilicate.
- Carbonates. This class includes about 80 mineral rocks. Dolomites, calcites and magnets are common here. The origin is due to individual aqueous solutions. Destroyed in acids.
- Halides are a group of one hundred different minerals. They are readily soluble, formed from sedimentary rocks. The most common substance is halite.
- Sulfides are minerals that are destroyed in the weathering zone. A typical representative is pyrite.
- sulfates. They have a light color and a low level of hardness. Gypsum is the most widely used.
- oxides and hydroxides. They make up about 17% of the mass of the earth's crust. The main types are opals, limonites and quartz.
Thus, almost all minerals have similar features, although the composition of the substances is different.
Variety of minerals
What is a mineral? It is not easy to answer this question. It should be taken into account that in today's world there are more than 4 thousand different types of underground wealth. Minerals open and "close" annually. For example, a substance found in rocks by its very existence proves the inconsistency of the whole classification compiled by scientists. Such cases are far from uncommon.
A photo of silicates is presented to your attention below.
It should be borne in mind that 4 thousand minerals is not such a big figure. When compared with the total inorganic compounds, then the difference will be obvious: the latter contains about a million species. How do geologists explain such a poor variety of mineral wealth? First, the prevalence of elements in solar system. Our planet is dominated by silicon and oxygen. The combination of these substances leads to the appearance of silicates - the overwhelming mineral group on Earth. On the other hand, the minerals are so scattered that the search for new elements will be the work of several hundred more generations. The second reason for the limited nature of minerals is the instability of most chemical compounds.
Origin of minerals
Scientists name three main ways of origin of mountain minerals. The first option is called endogenous. Underground hot alloys, which are commonly called magmatic matter, are introduced into the earth's crust, and then solidify there. Magma itself is formed as a result of volcanic eruptions. It goes through three stages: from a hot state, magma becomes solid - this is the result of pegmatite processes. After that, she finally freezes. This is a consequence of postmagmatic processes.
There is also an exogenous version of the origin of minerals. In this case, physical and chemical decomposition of substances occurs. At the same time, new formations are formed that are highly compliant to the environment. A simple example: as a result of weathering of endogenous material, crystals are formed.
The last way of origin of minerals is metamorphic. All substances will change under the influence of certain conditions - regardless of the options for the formation of rocks. In fact, the original sample is changing - it acquires new properties and composition elements.
Properties of minerals
The most important property of any mineral formation is the presence of a crystal-chemical structure. All other features of the considered breeds follow precisely from this.
To date, a unified classification of diagnostic features characteristic of mineral substances has been developed. Here it is necessary to highlight the hardness, determined on the Mohs scale, as well as color, gloss, fracture, cleavage, magnetism, brittleness and tint. Each property of the rocks under consideration will be studied in detail below.
The concept of hardness
What is hardness? There are several definitions for this concept. The most common description characterizes hardness as a level of resistance certain body scratching, squeezing or cutting impact. The hardness level is determined on the Moss scale. It contains special rocks, each of which is characterized by the ability to scratch surfaces with a sharp end. Moss made the top ten of the most common elements. The softest material here is talc and gypsum. As you know, gypsum, getting into the water, increases in size up to 30%. The hardest type and rock of the mineral is diamond.
Carrying the substance over the glass should leave behind scratches of various depths. The very fact of the existence of a scratch already assigns to the mineral at least the fifth class out of ten. The hardest substances are found in groups of minerals that have a non-metallic luster. It is brilliance that is the second important property of minerals, and it is directly related to hardness.
Shine
The level of brilliance of metals is checked by reflecting the rays of the sun from them. There are two levels of gloss - metallic and non-metallic. The first group includes rocks that give a black line when carved on glass. Such substances are opaque even in very thin fragments. Types of underground minerals with non-metallic luster include graphite, magnetite, coal and some other substances. All of them are poorly reflected in the sun and give a dark line. A small part of materials with a metallic sheen are substances that give a color line: green (gold), red (copper), white (silver), etc.
Minerals with a metallic sheen reflect better sunlight. By themselves, they have a high hardness. Special place here occupies ore.
Color
Color, unlike hardness and gloss, is not constant sign for most minerals. Thus, the hardness or luster remains unchanged over time. The color changes depending on storage conditions. Examples of minerals that rarely change color are malachite, which never changes its green color, and gold, which always remains yellow.
You can see a photo of malachite below.
The color also changes depending on the state of the mineral. For example, in geology, the concept of line color is common. A mineral that scratches a glass surface leaves behind a small amount of powder, which forms a line. The color of such a powder often differs from the natural color of the stone. It's all about the composition of the mineral: it may include calcite, which changes color depending on the amount and method of mixing with other substances.
Fracture and cleavage
Cleavage refers to the property of a mineral to split or split in a certain direction. So, after a break, a smooth shiny surface is most often formed. To achieve this result, you need to split the mineral along a strictly defined line. There are five gradations of cleavage:
A diagnostic feature for many minerals is the presence of several cleavage directions at once. As a result of splitting, the mineral has kinks, which also has certain properties. So, scientists distinguish five types of fracture:
- conchoidal - similar to a shell;
- splintery - fracture is characterized by fibrous or fibrous materials;
- uneven - the presence of imperfect cleavage (for example, in apatite);
- stepped - according to the results of cleavage, an almost perfectly smooth surface is formed (in places it may, however, have irregularities in the form of steps);
- smooth - according to the results of soldering, there are no noticeable bends or irregularities on the surface of the mineral.
There are a number of other signs by which minerals can be identified. This, for example, tarnish - the presence of a thin colored film formed on the substance as a result of weathering or oxidation. It is also necessary to highlight fragility, indicating the strength of the mineral, and magnetism, characterized by the content of ferrous iron.
Minerals in industry
In what areas social activities minerals used? These are construction, metallurgy, as well as chemical production.
Building materials are often diluted with certain minerals, which allows you to adjust the strength and quality of the substance. In the chemical industry, the presence of the elements in question is also not uncommon. Mineral components are used in cosmetic, medical and food fields. For example, in pharmacies there are many drugs that include vitamins and minerals. These two components work well together and complement each other. They help improve people's health and improve their appearance.
The extraction and study of minerals have always been considered important and relevant activities. It is necessary to fully support the conduct of scientific research in the field of geology, as well as the active use of vitamins and minerals in everyday life.
Now ~ 3000 minerals are known and every year their number increases. How to navigate in this numerous and diverse world of minerals? To do this, scientists group or systematize them on the basis of some signs. That is, they are classified. In mineralogy, there have been attempts to create a classification based on various features: for example, by hardness, brilliance, or cleavage; according to the conditions of education or genesis. But there are minerals that can form perfectly in different conditions. Since the middle of the last century, minerals began to be classified according to chemical composition- according to the dominant anion or anionic group. But only after the advent of X-ray diffraction analysis and the determination of the internal structure of minerals with its help, it became possible to establish a close relationship between the chemical composition of the mineral and its crystal lattice. This discovery laid the foundation for the principle of crystal chemical classification of minerals. This was first done by scientists Bragg and Goldschmidt for silicates.
For the main unit in this classification, a mineral species is taken, which has a certain crystalline structure and a certain stable chemical composition. The mineral species may have varieties. A variety is understood to mean minerals of the same type that differ from each other in some physical feature, for example, the color of the quartz mineral in numerous varieties (black - morion, transparent - rock crystal, purple - amethyst).
In the process of mineral formation, minerals of the same mineral species may differ from each other in appearance - crystal size or shape. In this case, each mineral of one mineral species is called a mineral individual.
Existing classifications unite mineral species into classes or groups. Their number varies by different authors, as the classification is improved and new data on mineral species are obtained. We will look at eight classes:
Characteristics of minerals by class
1. Native
2. Sulfides
3. Oxides and hydroxides
4. Halides
5. Carbonates
6. Sulfates
7. Phosphates
8. Silicates
1. Native elements (minerals).
This class includes minerals that consist of one chemical element and are named after this element. For example: native gold, sulfur, etc. All of them are divided into two groups: metals and non-metals. The first group includes native Au, Ag, Cu, Pt, Fe, and some others; the second group includes As, Bi, S, and C (diamond and graphite).
Genesis - mainly formed during endogenous processes in intrusive rocks and quartz veins, S - during volcanism. During exogenous processes, the destruction of rocks occurs, the release of native minerals (due to their resistance to physical and chemical influences) and their concentration in places favorable for this. Thus, placers of gold, platinum and diamond can be formed.
Application in the national economy:
1 - jewelry production and foreign exchange reserves (Au, Pt, Ag, diamonds);
2 - religious objects and utensils (Au, Ag),
3 - radio electronics (Au, Ag, Cu), nuclear, chemical industry, medicine, cutting tools - diamond;
4 - agriculture - sulfur.
II. Sulfides are salts of hydrosulphuric acid.
They are divided into simple ones with the general formula A m X p and sulfosalts - A m B n X p, where -
A - a metal atom, B-atoms of metals and metalloids, X - sulfur atoms.
(Pb, Cu, Fe, etc.) (Bi, Sb, As, Sn)
Sulfides crystallize in different syngonies - cubic, hexagonal, rhombic, etc. Compared to native ones, they have a wider composition of elemental cations. From here more variety mineral species and a wider range of the same property.
General properties for sulfides are metallic luster, low hardness (up to 4), gray and dark colors, medium density.
At the same time, there are differences among sulfides in such properties as cleavage, hardness, and density. For example:
Sulfides are the main source of non-ferrous metal ores, and due to impurities of rare and noble metals, the value of their use increases.
Genesis - various endogenous and exogenous processes.
III. Oxides and hydroxides - represent one of the most common classes with over 150 mineral species in which metal atoms or cations form compounds with oxygen or a hydroxyl group (OH). This is expressed by the general formula AX or ABX - where X are oxygen atoms or a hydroxyl group. The most widely represented oxides are Si, Fe, Al, Ti, Sn. Some of them also form the hydroxide form. A feature of most hydroxides is a decrease in property values compared to the oxide form of the same metal atom. A striking example of p is the oxide and hydroxide form of Al.
Oxides according to their chemical composition and luster can be divided into: metallic and non-metallic. The first group is characterized by medium hardness, dark colors (black, gray, brown), medium density. An example is the minerals hematite and cassiterite. The second group is characterized by low density, high hardness 7-9, transparency, wide range of colors, lack of cleavage. Example p - minerals quartz, corundum.
In the national economy, oxides and hydroxides are most widely used to obtain Fe, Mn, Al, Sn. Transparent, crystalline varieties of corundum (sapphire and ruby) and quartz (amethyst, rock crystal, etc.) are used as precious and semi-precious stones.
Genesis - in endogenous and exogenous processes.
IV. Halides. The most widespread are fluorides and chlorides - compounds of metal cations with monovalent fluorine and chlorine.
Fluorides are light minerals, of medium density and hardness. Representative - fluorite CaF2. Chlorides are the minerals halite and selvin (NaCl and KCl).
For halides, the common features are low hardness, crystallization in the cubic system, perfect cleavage, a wide range of colors, and transparency. Halite and sylvin have special properties - salty and bitter-salty taste.
Fluorides and chlorides differ in genesis. Fluorite is a product of endogenous processes (hydrothermal), while halite and sylvin are formed under exogenous conditions due to precipitation during evaporation in water bodies.
In the national economy, fluorite is used in optics, metallurgy, to obtain hydrofluoric acid. Halite and sylvin are used in the chemical and food industries, in medicine and agriculture, photodele.
V. Carbonates - salts of carbonic acid, the general formula is ACO3 - where A is Ca, Mg, Fe, etc.
General properties a - crystallize in rhombic and trigonal systems (good crystalline forms and rhombus cleavage); low hardness 3-4, predominantly light color, reaction with acids (HCl and HNO3) to release carbon dioxide.
The most common are: calcite CaCO3, magnesite Mg CO3, dolomite CaMg (CO3) 2, siderite Fe CO3.
Carbonates with a hydroxyl group (OH):
Malachite Cu2 CO3 (OH) 2 - green color and reaction with HC l,
Azurite Cu3 (CO3) 2 (OH) 2 - Blue colour, transparent in crystals.
The genesis of carbonates is diverse - sedimentary (chemical and biogenic), hydrothermal, metamorphic.
These are rock-forming minerals of sedimentary rocks (limestone, dolomites, etc.) and metamorphic minerals - marble, skarns. They are used in construction, optics, metallurgy, as fertilizers. Malachite is used as an ornamental stone. Large accumulations of magnesite and siderite are a source of iron and magnesium.
VI. Sulfates are salts of sulfuric acid, i.e. have a SO4 radical. The most common and well-known sulfates are Ca, Ba, Sr, Pb. Common properties for them are - crystallization in monoclinic and rhombic systems, light color, low hardness, vitreous luster, perfect cleavage.
Minerals: gypsum CaSO4 *2H2O, anhydrite CaSO4, barite BaSO4 (high density), celestite SrSO4.
Formed under exogenous conditions, often together with halides. Some sulfates (barite, celestite) have a hydrothermal origin.
Application - construction, agriculture, medicine, chemical industry.
III. Phosphates - salts phosphoric acid, i.e. containing PO4.
The number of mineral species is small, we will consider the mineral apatite Ca(PO4) 3 (F, Cl, OH). It forms crystalline and granular aggregates, hardness 5, hexagonal syngony, imperfect cleavage, green-blue color. Contains impurities of strontium, yttrium, rare earth elements.
The genesis is igneous and sedimentary, where it forms phosphorite in a mixture with clay particles.
Application - agricultural raw materials, chemical production and in ceramic products.
VIII. Silicates are the most common and diverse class of minerals (up to 800 species). Silicate taxonomy is based on the silicon-oxygen tetrahedron -4. Depending on the structure that they form when combined with each other, all silicates are divided into:
island, layer, tape, chain and frame.
Island silicates - in them, the connection between isolated tetrahedra is carried out through cations. This group includes minerals: olivine, topaz, garnets, beryl, tourmaline.
Layer silicates - represent continuous layers, where the tetrahedra are connected by oxygen ions, and between the layers the connection is carried out through cations. Therefore, they have a common radical in the formula 4. This group combines micas minerals: biotite, talc, muscovite, serpentine.
Chain and ribbon - tetrahedra form single or double chains (ribbons). Chain - have a common radical 4- and include a group of pyroxenes.
Ribbon silicates with a radical 6 - combine minerals of the amphibole group.
Framework silicates - in them, tetrahedra are interconnected by all oxygen atoms, forming a framework with a radical. This group includes - feldspars and plagioclases. Feldspars combine minerals with Na and K cations. These are microcline and orthoclase minerals. In plagioclases, Ca and Na are cations, while the ratio between these elements is not constant. Therefore, plagioclases are an isomorphic series of minerals:
albite - oligoclase - andesine - labradorite - bytonite - anorthite. From albite to anorthite, the content of Ca increases.
The composition of cations in silicates most often contains: Mg, Fe, Mn, Al, Ti, Ca, K, Na, Be, less often Zr, Cr, B, Zn rare and radioactive elements. It should be noted that part of the silicon in the tetrahedra can be replaced by Al, and then we classify the minerals as aluminosilicates.
The complex chemical composition and the diversity of the crystal structure, combined, give a wide range of physical properties. Even using the example of the Mohs scale, it can be seen that the hardness of silicates is from 1 to 9.
Cleavage from very perfect to imperfect. There is nothing to say about coloring - the widest range of colors and shades.
At the same time, within each structural group, the properties are close and there is always one or two signs by which a mineral can be identified. For example, micas are defined by cleavage and low hardness.
Often silicates are grouped by color - dark-colored, light-colored. This is especially widely applied to silicates - rock-forming minerals.
Silicates are formed mainly during the formation of igneous and metamorphic rocks in endogenous processes. A large group of clay minerals (kaolin, etc.) is formed under exogenous conditions during the weathering of silicate rocks.
Many silicates are minerals and are used in the national economy. These are building materials, facing, ornamental and precious stones (topaz, garnets, emerald, tourmaline, etc.), ores of metals (Be, Zr, Al) and non-metals (B), rare elements. They find application in the rubber, paper industry, as refractories and ceramic raw materials.
The classification of minerals is based on the chemical composition:
Table 1 -
The sequence of actions in determining the hardness of minerals: a mineral is drawn on glass (tv. 5). If a scratch remains on the glass, then the hardness of the mineral is equal to or greater than 5. Then reference minerals with a hardness greater than 5 are used. For example, if the tested mineral leaves a scratch on a reference with a hardness of 6, and scratching it with quartz results in a deep scratch, then its hardness is 6, 5.
Some minerals have special properties that are unique to them. So carbonates react with hydrochloric acid (calcite “boils” in a piece, dolomite in powder, magnesite in hot acid).
Halides have a characteristic taste (halite - salty).
Minerals are characterized by varying resistance to weathering. Some minerals are destroyed physically, forming fragments, other minerals undergo chemical transformations, being converted into other compounds (table 2).
Resistance of minerals to weathering
table 2
Group according to the degree of stability | Name of minerals | The nature of the changes |
The most stable, insoluble | Quartz Muscovite Limonite | Physical grinding without changing the chemical composition |
Medium resistant, insoluble | Orthoclase Albite Augit Hornblende | Physical destruction and hydrolysis: secondary minerals are formed: kaolinite, limonite, opal |
Less stable, insoluble | Labrador Biotite | The same, but the process is more intense |
Weakly stable, insoluble | Pyrite Olivine | Oxidation: limonite and sulfuric acid are formed Oxidation: serpentine, chlorite, magnesite are formed |
slightly soluble | Dolomite Calcite | Physical disintegration and dissolution |
Medium soluble | Anhydrite Gypsum | Dissolution, hydration, dehydration |
highly soluble | Halite | Intensive dissolution, plastic flow with prolonged action of one-sided exposure |
Method for the determination of minerals.
To perform practical work, it is necessary to use the determinant of minerals.
Work sequence:
1. Determine the appearance of the grains of the mineral aggregate.
2. Determine the color of the mineral, if the mineral is dark, then run the mineral over a porcelain plate to determine the color of the line (powder).
3. Determine the brilliance of the mineral.
4. To determine the hardness range, pass the mineral over the glass.
5. Minerals of medium hardness (3-3.5) should be checked for reaction with a 10% hydrochloric acid solution.
6. Try to find smooth polished edges on the sample - i.e. determine cleavage.
7. Find the name and composition of the mineral by the set of features in the determinant.
8. Mark the composition of which rocks this mineral is included.
Enter data on minerals in table 3.
Characteristics of rock-forming minerals
Table 3
Exercise
List of minerals to study:
1. Native elements: graphite, sulfur.
2. Sulfides: pyrite.
3. Oxides and hydroxides: quartz, chalcedony, opal, limonite.
4. Halides: halite, sylvin.
5. Carbonates: calcite, dolomite, magnesite.
6. Sulphates: gypsum, anhydrite.
7. Silicates: olivine, garnet, augite, hornblende, talc, serpentine, kaolin, micas, chlorite, orthoclase, microcline, albite, nepheline.
BIBLIOGRAPHY
Pavlinov V.N. et al. Manual for laboratory studies in general geology. - M.: Nedra, 1988. p. 5-7, 11-49.
The study of igneous rocks
The purpose of the work: to acquire skills in the identification of igneous rocks. To study the engineering and construction characteristics of igneous rocks and their application in construction.
Equipment: educational collection of igneous rocks, magnifiers, Mohs scale.
General information about rocks
Rocks are called independent geological bodies, consisting of one or more minerals of more or less constant composition and structure.
According to the method and conditions of formation, all rocks are divided into igneous, sedimentary and metamorphic.
The mineralogical composition of rocks is different. They can consist of one (monomineral) or several minerals (polymineral).
The internal structure of rocks is characterized by their structure and texture.
Structure - this is the structure of the rock, due to the shape, size and relationship of its constituent parts.
The texture of the rock determines the distribution of its constituent parts in space.
All rocks are classified according to the conditions of formation into igneous, sedimentary and metamorphic rocks.
Conditions for the formation of igneous rocks
Igneous rocks are formed as a result of the cooling of magma. Magma is a stone melt of a silicate composition, which is formed at great depths in the bowels of the Earth. Magma can cool deep in the earth's crust under the cover of overlying rocks and on or near the surface of the earth. In the first case, the cooling process proceeds slowly, and all the magma has time to crystallize. The structures of such deep rocks are fully crystalline and granular.
With the rapid rise of magma to the surface of the earth, its temperature drops rapidly, gases and water vapor are separated from the magma. In this case, the rocks are either not completely crystallized (glassy structure) or partially crystallized (semicrystalline structure).
Deep rocks are called intrusive. Their structures can be: fine-grained (grains<0,5 мм), среднезернистая (размер зерен 0,5-1 мм), крупнозернистая (от 1 до 5 мм), гигантозернистая (>5 mm), uneven-grained (porphyritic).
Erupted rocks are called effusive. Their structures are porphyritic (separate large crystals stand out in the cryptocrystalline mass), aphanitic (dense cryptogranular mass), glassy (the rock almost entirely consists of a non-crystallized mass - glass).
Textures of igneous rocks: intrusive rocks are almost always massive. In effusive rocks, along with a massive texture, there are porous and vesicular ones.
The physicochemical conditions of rock formation at depth and on the surface are sharply different. For this reason, different rocks are formed from magma of the same composition under deep and surface conditions. Each intrusive rock corresponds to a certain outflowing rock.
Along with the classification of igneous rocks according to the conditions of occurrence, they are classified according to their chemical composition depending on the content of silicic acid SiO 2 (Table 4).
Classification of igneous rocks
Table 4
Breed composition | Rocks are intrusive (deep) | Effusive rocks (poured out) | |
chemical | mineralogical | ||
Acidic SiO 2 > 65% | Quartz, feldspar, mica | Granite | Liparite, pumice, quartz porphyry, obsidian |
Medium SiO 2 (65-52%) | Potassium feldspar, plagioclase, hornblende Plagioclase, hornblende | Syenite Diorite | Trachyte, orthophyre Andesite, andesite porphyrite |
Basic SiO 2 = 52-40% | Plagioclase, pyroxene Plagioclase | Gabbro Labradorite | Basalt, diabase |
Ultrabasic SiO 2< 40 % | Olivine Olivine, pyroxene Pyroxene | Dunite Peridotite Pyroxenite |
Engineering and construction characteristics of igneous rocks.
All igneous rocks have high strength, significantly exceeding the loads possible in engineering and construction practice, are insoluble in water and practically impermeable (except for fractured varieties). Due to this, they are widely used as foundations for critical structures (dams). Complications during construction on igneous rocks arise if they are fractured and weathered: this leads to a decrease in density, an increase in water permeability, which significantly worsens their engineering and construction properties.
Application in construction
Intrusive igneous rocks such as granite, syenite, diorite, gabbro, labradorite are used as facing material.
Engineering-geological properties of metamorphic rocks
Massive metamorphic rocks are highly durable, practically impermeable and, with the exception of carbonates, do not dissolve in water.
The weakening of the strength indicators occurs due to fracturing and weathering.
Shale rocks are characterized by anisotropic properties, i.e. strength is much lower along the schistosity than perpendicular to it. Such metamorphic rocks form thin-platy mobile talus.
The most durable and stable rocks are quartzites. Metamorphic rocks are widely used in construction. Marbles, quartzites are facing material.
Roofing slates (phyllites) serve as a material for covering buildings.
Talc shale is a refractory and acid-resistant material.
Quartzite is used as a raw material for the production of refractory bricks - dinas.
Method for determining metamorphic rocks
The definition of metamorphic rocks must begin with the establishment of their mineral composition. The texture, structure, color and parent rock are then determined.
EXERCISE
Explore by outward signs metamorphic rocks in the study collection. Describe them in a notebook according to the following plan:
1. Name;
3. Structure and texture;
4. Mineral composition;
5. Initial breed;
6. Engineering and geological features;
7. Application in construction.
BIBLIOGRAPHY
Pavlinov V.N. et al. Manual for laboratory studies in general geology. - M.: Nedra, 1988. p. 77-85.
Geological maps and sections
The purpose of the work: to master the principle of constructing geological maps and sections. Learn to read the symbols of geological maps. Acquire skills in determining the conditions for the occurrence of rocks on geological maps.
General information
The geological map reflects geological structure earth's surface and the adjacent upper part of the earth's crust. A geological map is built on a topographic basis. On it, with the help of conventional signs, the age, composition and conditions of occurrence of rocks exposed on the earth's surface are shown.
Since more than 90% of the land surface is covered with rocks of the Quaternary age, geological maps show bedrocks without a Quaternary cover.
For construction purposes, large-scale geological maps (1:25000 and larger) are used.
When compiling geological maps, it is necessary to know the age (geochronological) sequence of rocks involved in the structure of the area under study.
At present, a unified geochronological scale has been created, reflecting the history of the development of the earth's crust.
The following temporal and corresponding stratigraphic (stratum - layer) divisions are accepted in the scale (Table 6).
Geochronological and stratigraphic divisions
Table 6
Geological scale
Table 7
Era (band) | Period (system) | Index | Duration million years | Epoch (department) | Index | Color on the map |
Cenozoic KZ 65 Ma | Quaternary | Q | 1,7-1,8 | Holocene Pleistocene | Q 2 Q 1 | Pale gray |
Neogene | N | Pliocene Miocene | N 2 N 1 | Yellow | ||
Paleogene | R | Oligocene Eocene Paleocene | R 3 R 2 R 1 | orange yellow | ||
Mesozoic MZ 170 million years | Chalky | TO | Upper Cretaceous Lower Cretaceous | K 2 K 1 | Green | |
Jurassic | J | 55-60 | Upper Jurassic Middle Jurassic Lower Jurassic | J 3 J 2 J 1 | Blue | |
Triassic | T | 40-45 | Upper Triassic Middle Triassic Lower Triassic | T 3 T 2 T 1 | Violet | |
Paleozoic РZ | Permian | R | 50-60 | Upper Perm Lower Perm | R 2 R 1 | orange brown |
Coal | WITH | 50-60 | Upper Carboniferous Medium Carboniferous Lower Carboniferous | S 3 S 2 S 1 | Grey | |
Devonian | WITH | Upper Devonian Middle Devonian Lower Devonian | D 3 D 2 D 1 | Brown | ||
Silurian | S | 25-30 | Upper Silurian Lower Silurian | S 2 S 1 | Grey-green (light) | |
Ordovician | ABOUT | 45-50 | Upper Ordovician Middle Ordovician Lower Ordovician | O 3 O 2 O 1 | Olive | |
Cambrian | Є | 90-100 | Upper-Kembirsky Middle-Kembirsky Lower-Kembirsky | Є 3 Є 2 Є 1 | Blue-green (dark) | |
Proterozoic PR | Lilac pink | |||||
Archean AR | Pink |
Conventional signs on geographical maps
To indicate the composition, time of formation and conditions of occurrence of rocks on geological maps, color, alphabetic, digital and dash symbols are used.
Color signs are used to indicate the age of rocks, as well as the composition of intrusive and volcanic rocks (see geochronological scale). Letters and numbers (indices) indicate age, and for intrusive and volcanic rocks, their composition. For example (Figure 1):
Figure 1 - Designation of the age of rocks
Stratigraphic terms are used in relation to rocks, for example: rocks of the Carboniferous system (and not of the period).
To designate the genesis of sedimentary rocks, lowercase Latin letters are used: m - marine, g - glacial, and - alluvial. For example: aQ - alluvial Quaternary deposits.
Intrusive and effusive rocks are indexed using capital Greek letters: γ - granites, δ - diorites, ξ - syenites, ν - gabbro, σ - dunites.
Line designations are usually used on geological maps made in one color, as well as on sections and in stratigraphic columns.
The most commonly used stroke symbols are shown in Figure 2.
1 - sands; 2 - sandstones; 3 - pebbles; 4 - conglomerates; 5 - siliceous rocks (jaspers, flasks, diatomites); 6 - limestones; 7 - dolomites; 8 - clay; 9 - marls; 10 - rocks of acidic composition; 11 - their lavas and tuffs; 12 - rocks of average composition; 13 - their lavas and tuffs; 14 - rocks of the main composition; 15 - their lavas and tuffs.
Figure 2 - Dash symbols
Layer and layering
A layer (or stratum) is a more or less homogeneous isolated sediment (or rock) bounded by stratification surfaces.
The upper surface is called the roof, the lower - the sole. The distance between the roof and the sole characterizes its power.
Two cases of correlation of layered thicknesses are possible. In the first case, each overlying stratum, without traces of a break in the accumulation of sediments, rests on the underlying layers, forming a consistent bedding of rocks.
In the second case, the stratigraphic sequence is interrupted between the strata and, as a result, a stratigraphic e disagreement, which can be angular (Figure 3).
Figure 3 - Unconformity of rock formation
Stratigraphic columns and geological sections
Geological maps are usually accompanied by stratigraphic columns and sections. Pre-Quaternary sedimentary, volcanic and metamorphic rocks developed on the territory are depicted in the stratigraphic column in the age sequence from bottom to top from ancient to young. Intrusive formations are not shown on the column.
Geological sections represent the image of the occurrence of rocks on the plane of the vertical section of the earth's crust from its surface to a particular depth.
The horizontal and vertical scales of the sections should correspond to the scale of the map (except when the bedding of the rocks is horizontal). Each section shows: a hypsometric profile of the terrain, a sea level line, a vertical scale with divisions every 1 cm at both ends of the section.
The sections are colored and indexed according to the geological map.
With horizontal occurrence of layers, sections are usually built through the highest and lowest points of the relief.
During construction, it is important to know the geological structure of the upper part of the earth's crust. The upper horizons are mainly characterized by the horizontal occurrence of rocks.
Guidelines and task for constructing a geological section
In the appendix (issued by the teacher) a geological map of the river basin is given. Kacha and stratigraphic column. It is necessary to study the sequence of occurrence of rocks along the core, their description, age, thickness. Glue a photocopy of the map on an A4 sheet of paper, and draw a stratigraphic column to the left of the map. Place symbols on the right. The geological section is made at the bottom (Figure 4).
Geological map of the river basin. Kacha
Scale 1:25000
|
Geological section along AB
Mountain scales.
Figure 4 - Location of drawing elements
The construction of the section begins with drawing the profile of the section. To do this, several horizontal lines are drawn on a sheet of drawing paper, the distance between which should be equal to the section of the relief by contour lines on the scale of the map. In a given map, horizontal lines cut the relief every 10 m, which on a scale of 1:10000 will be 1 mm. The rulers are limited to vertical lines located at a distance corresponding to the length of the cut. The vertical rulers on both sides of the section indicate the heights corresponding to the height of contour lines on the map intersected by the section line. Next, the distances to the section line are measured on the map to the intersection with contour lines and these distances are transferred to rulers having the same elevation marks. The obtained points are connected by a smooth curve, which will represent the relief profile.
Having drawn the relief curve of the Earth's surface along the cut line, all points of intersection of the cut line with the geological boundaries are transferred to it. For this purpose, you can use either a measuring compass or a separate narrow strip of paper. Having found the exit points of the geological boundaries on the surface of the relief, we draw horizontal lines between the stratigraphic complexes. Letters A and B are placed at the ends of the section, and indices and conditional shading for rocks are applied to the section itself.
Exercise
Construct a geological section along the line proposed by the teacher, using the training map in the application (provided by the teacher).
Bibliography
Pavlinov V.N. et al. Manual for laboratory studies in general geology. - M.: Nedra, 1988. S. 86-102.
Assessment of engineering-geological conditions of construction
The purpose of the work: to acquire the skills of processing the primary data of engineering and geological surveys and their evaluation. Equipment: paper sheet 70x30 cm, drawing accessories.
Modern construction methods make it possible to master even very difficult natural conditions plots, but this requires a large additional investment. The assessment of the feasibility of such costs and the suitability of a particular area for construction is always associated with the establishment of the volume of engineering measures necessary for the development of the site.
For this purpose, engineering and geological surveys are carried out, the analysis of which allows:
1. Assess the engineering and geological conditions for the construction of structures, assess the possible impact of structures on the state and properties of rocks and the stability of the territory as a whole;
2. Establish the nature of engineering measures that ensure the stability and reliability of structures.
By doing this final work, the student gains some skills in processing the primary data of engineering-geological surveys and their evaluation.
Exploratory drilling and leveling data are used as source materials.
The work consists of two stages:
1) construction of a geological section based on well drilling data;
2) drawing up an explanatory note to the constructed section.
Methodology for constructing a geological section.
The student performs that version of the task, the number of which matches the last digit of his cipher. Based on the leveling and drilling data, construct a geological section on the following scales: horizontal 1: 5000, vertical
1:500. Drilling data in the application (provided by the teacher).
To build a section, you need a sheet of whatman paper 70 x 30 cm. The drawing is made in pencil.
On the left side of the sheet, we draw a vertical scale bar in the accepted scale (1: 500). The maximum mark on this ruler is equal to the maximum absolute mark of the terrain (according to the leveling data), the minimum mark is equal to the lowest absolute mark of the bottom hole (well drilling depth). Under the scale bar we draw a conditional base line, equal to the length incision. Next, on the baseline we put on a horizontal scale (1: 5000) the distance between the points in accordance with the leveling data. From the points we restore the perpendiculars to the absolute marks of the earth's surface (wellheads).
By connecting the wellheads with a smooth line, we get the line of the topographic profile (the surface of the earth). Next to the wellhead, we indicate the number and absolute mark of the wellhead. On the axial lines of the wells, with small horizontal strokes, we show the boundaries of the distribution of thickness in m of certain rocks from top to bottom, and next to it we indicate the lithological composition and age of the rocks with symbols, that is, we plot the sections of these boreholes.
Next, we connect the strokes depicting the boundaries of rocks of the same composition and age in neighboring wells. If the rock found in one well is absent in the next one, then on the section we depict it as a gradual wedging out to the middle of the distance between the wells. After linking all the boundaries of the rocks, the areas between the wells are shaded according to the symbols (Figure 2).
We mark the mark of the appearance of the groundwater level next to the development on the right at a height corresponding to this mark.
We connect the position of the groundwater level into a single dotted line, and show the established levels of pressure waters next to the working with a vertical arrow to the height of the water pressure (from the mark of appearance to the mark of the establishment of pressure waters).
Symbols of rocks are placed in a strict sequence from younger to older and are applied to the right of the section (from top to bottom) or under the section (from left to right). We sign the cut below. For example: "Geological and lithological section along the line of wells (1-5)". Under the name in the middle we put the scale horizontal and vertical.
An explanatory note must be attached to the geological and lithological profile, including a description of:
1) terrain;
2) geological structure;
3) hydrogeological conditions;
4) engineering and geological conditions of construction.
Terrain relief.
It is necessary to indicate the type of relief (mountainous or flat), the degree of its ruggedness and the absolute marks of individual elements. Particular attention is drawn to the description of the river valley: the length, width, depth of the riverbed, the presence of terraces, their height above the water level, the width, the steepness of the primary slopes.
According to the location relative to the channel, symmetrical and asymmetric terraces are distinguished, as well as a two-sided and one-sided floodplain. According to the formation conditions, the terraces are divided into accumulative (completed entirely by alluvium), erosional (composed entirely by bedrock) and socle (in which part of the slope above the river is represented by bedrock covered from above with a layer of alluvium).
Geological structure.
The lithological and stratigraphic characteristics of the rocks and the conditions of their occurrence are given here.
First, the age of bedrocks and the conditions of their occurrence, as well as the genetic varieties of Quaternary deposits, are given.
Eluvium (e) - clastic material is formed under the influence of weathering and forms an accumulation at the site of destruction.
Deluvium (d) - clastic material is carried down the slope by rain or melt water and accumulates on the slope or at the foot of the hills.
Proluvium (r) - destruction products carried by powerful temporary flows (mudflows) to the foot of the hills and located in the form of alluvial fans.
Alluvium (a) - deposits formed in river valleys by river flows.
Colluvium (q) - clastic deposits moved downslope by gravity.
Fluvioglacial (fq) - deposits of glacial melt water flows below the edge of the glacier.
Then proceed to a detailed description of the breed according to the plan:
a) breed name, genesis group, age;
b) mineralogical composition, structure, texture;
c) power and its change along the profile;
d) conditions of occurrence.
The breeds are described in order of age from ancient to young.
hydrogeological conditions.
When characterizing hydrogeological conditions, the presence of various types of groundwater and the total number of aquifers are noted. For each aquifer, the following information is given: the type of groundwater (top water, groundwater, interstratal, fissure), pressure or non-pressure.
It is necessary to pay attention to the hydraulic connection between adjacent aquifers (the connection is established by the coincidence of piezometric levels between pressure horizons, or with the horizon of overlying groundwater).
Engineering-geological conditions of construction.
The evaluation of the engineering-geological conditions of construction is given in the form of an analysis of the engineering-geological properties of rocks (density, humidity, water permeability, resistance to mechanical stress, subsidence, swelling, landslide, karst formation and other geological phenomena).
Requirements for the composition and design of the work.
The volume of the explanatory note is 5-6 pages of handwritten text on A4 sheets. The title page is made according to the generally accepted requirements for written work, indicating the option number.
Literature is required to complete the work.
The text should be concise and at the same time detailed and exhaustive.
At the end of the work there is a list of used literature.
BIBLIOGRAPHY
Ananiev V.P. Engineering geology. - M.: graduate School, 2000.
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
To date, 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
At the moment, the most common is the classification of minerals by chemical composition, which is used by modern mineralogists and geologists. It is based on the nature of the compounds, 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.
- native elements;
- sulfides;
- oxides and hydroxides;
- salts of oxygen acids;
- halides.
Further, according to the nature of the anions, they are divided into several classes (each type has its own division), within which they are already divided into subclasses, from which it is possible to distinguish: frame, chain, island, coordination and layered mineral. The classification of minerals that are close to each other in composition and have a similar structure provides for their association into various groups.
Characteristics 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 salts such as pyrite, galena and others in this group.
- Oxides, hydroxides and their other analogues, which are a combination of a metal with oxygen. Magnetite, chromite, hematite, goethite are the main representatives of this category, which are distinguished by the chemical classification of minerals.
- Salts of oxygen acids.
- Halides.
It is also worth noting that in the group "salts of oxygen acids" there is also a classification of minerals by class:
- carbonates;
- sulfates;
- tungstates and molybdates;
- phosphates;
- silicates.
There are also three groups:
- igneous;
- sedimentary;
- metamorphic.
Origin
The classification of minerals by origin includes three main groups:
- Endogenous. Such processes of mineral formation in the 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, they will 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. It includes:
- gems;
- colored stones;
- organic 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 body the scratching effect of another. Thus, if the mineral in question is softer than the one with which its surface is scratched, traces 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 hardest substance.
Initially, it was customary to carry out the breed 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 according to 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, he left a scratch on the sample, but did not leave apatite, which is at number 5, he is assigned class 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 shine 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:
- with a metallic sheen;
- with non-metallic luster.
The former include those rocks that give a black line and are opaque even in fairly thin fragments. These include magnetite, graphite and coal. Minerals with a non-metallic luster and a color streak are also considered here as an exception. This applies to gold with 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 luster of a fresh fracture of various metals, and can be seen quite well on the fresh surface of the sample, even if considered. The classification of products with such a luster also includes opaque samples, which are heavier than the first category.
Metallic luster is characteristic of minerals, which are ore of various metals.
Color
It should be noted 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 obtain a fresh chip.
Special attention should be paid to the fact that the classification of the properties of minerals also includes such a concept as the color of the line (ground powder), which often does not differ from the standard one. 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.
The powder, or trait of the mineral, is obtained on porcelain, which should not be covered with any glaze and is simply called "biscuit" among professionals. 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 certain part from them to white paper, and then grind to the desired state.
Cleavage
This concept implies the property of a mineral to split or split in a certain direction, while 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, five main gradations of cleavage are provided:
- very perfect - the mineral can be easily split into small plates;
- perfect - with any blows with a hammer, 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 - is found with certain difficulties;
- very imperfect - cleavage is practically absent.
Certain minerals have several directions of cleavage 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:
- even - there are no noticeable bends on the surface, but at the same time it is not mirror-smooth, as is the case with cleavage;
- stepped - characteristic of crystals that have a 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;
- splintery - characteristic of fibrous minerals and is somewhat similar to a fracture of wood across the fibrous structure;
- conchoidal - in the shape of its surface it is similar to a shell;
Other properties
A fairly 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 material being tested is taken, after which it is touched with a magnetized knife or horseshoe. If, after this procedure, the particles of the mineral begin to attract, this indicates that it has 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, which contain carbonic salts, under the influence of of hydrochloric acid begin to allocate carbon dioxide, which manifests itself in the visage of bubbles, which is why many people call it "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 also applies to 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, after which, using tweezers, bring it directly into the flame from a gas burner, spirit lamp or candle.
Forms of their presence in nature
In the predominant 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 that have an internal. 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 maintaining the third in a short form.
It should be noted that some minerals can form naturally intergrown crystals, which are then called twins, tees and other names. Such samples are often the result of intergrowth or intergrowth of crystals.
Kinds
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 provides for the possibility of free growth of minerals.
Among other things, many crystalline minerals are distinguished by rather complex irregular shapes, which leads to the formation of dendrites, sinter forms, and others. The formation of dendrites is carried out 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 secretion. They use a concentric structure, and the mineral substance fills it to the center from the periphery. Sufficiently large secretions, in which an empty space remains inside, it is customary to call geodes, while small formations are called tonsils.
Concretions are concretions of an 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 occurs, on the contrary, towards the periphery from the center.
Minerals are called natural chemical compounds or individual chemical elements that have arisen as a result of physical and chemical processes occurring in the Earth. IN earth's crust minerals are predominantly in the crystalline state, and only a small part is in the amorphous state. The properties of crystalline substances are determined both by their composition and internal structure, i.e. crystal structure. In crystal lattices, the distances between elementary particles and the nature of the connections between them in different directions are not the same (Fig. 2.1), which also determines the difference in properties. This phenomenon is called anisotropy or non-equilibrium of a crystalline substance. The anisotropy of crystalline substances is manifested in many of their features. For example, in the ability of a crystalline substance to self-cut, i.e. form polyhedra - crystals, the shape of the crystals is diverse and depends primarily on the internal structure of the given compound.
The manifestation of anisotropy can be considered using the graphite mineral as an example, the internal structure of which is shown in Fig. 2.1b. The distance between carbon atoms within the flat layers of the lattice is 0.14 nm (1.42 A), between the layers it is greater than 0.33 nm (3.39 A). This explains the ability of graphite to easily split (very perfect cleavage - see below) into thin sheets parallel to the layers of the lattice, and break with difficulty along uneven surfaces in other directions, where the distances between the particles and the adhesion forces between them are greater.
In amorphous substances, there is no regularity in the arrangement of particles. Their properties depend only on the composition and are statistically the same in all directions, i.e. amorphous substances are isotropic or are of equal properties. First of all, this is expressed in the fact that amorphous substances do not form crystals and do not have cleavage.
Under different physicochemical conditions, substances of the same chemical composition can acquire a different internal structure and, consequently, different physical properties and thus create different minerals. This phenomenon is called polymorphism (Greek "poly" - many). As shining example polymorphism, two modifications of carbon (C) can be named: the aforementioned mineral graphite and the mineral diamond. The internal structure of diamond differs sharply from the structure of graphite (Fig. 2.1, a). In the structure of diamond, the bonds between carbon atoms are of the same type and strong. From this follow the properties of diamond (C), which differ sharply from the properties of graphite (C): low hardness-1 and density-2.1-2.3 of graphite and high-diamond, respectively 10 and 3.5, etc.
An important property crystalline substances, due to the internal structure, is also its homogeneity, which is expressed in the fact that any parts of the crystalline substance in the same directions have the same properties, i.e. if a graphite crystal in one direction has a very perfect cleavage, then any of its fragments in the same direction has this property.
The forms of finding minerals in nature are diverse and depend mainly on the conditions of formation. These are either separate crystals or their natural intergrowths (twins), or clearly separated mineral accumulations, or, more often, accumulations of mineral grains - mineral aggregates.
Separate isolated crystals and crystalline twins, i.e. regular intergrowths of crystals appear in conditions favorable for growth. The shape of the crystals is varied and reflects both the composition and internal structure of the mineral, and the conditions of formation. Twins are regular intergrowths of crystals. Twinning laws are diverse, which leads to the formation of morphologically different twins.
Among the isolated mineral accumulations, the most common are druses, which are accumulations of crystals adhering to the walls of caves or cracks. Secretions are the result of the gradual filling of limited voids with mineral matter deposited on their walls. They usually have a concentric structure, reflecting the stages of formation. Small secretions are called tonsils, large secretions are called geodes. Concretions - more or less rounded formations that arose by the deposition of mineral matter around a center of crystallization. This is often associated with the concentric or radially radiant structure of concretions. Small rounded formations, usually concentric in structure, are called oolites. Their occurrence is associated with the precipitation of mineral matter in the mobile aquatic environment. Sinter formations that complicate the surfaces of voids arise during the crystallization of mineral matter from seeping groundwater. The incrustations hanging from the vaults of the voids are called stalactites, growing up from the bottom of the caves - stalagmites. On the surface of the cracks, flat mineral films with different structures can develop.
The most widely developed are mineral aggregates of crystalline, amorphous, or cryptocrystalline structures that make up rock strata. They are formed by more or less simultaneous precipitation of many mineral particles from solutions or melts. In crystalline aggregates, minerals are in a crystalline state, but their grains have irregular shape. The size of the grains depends on the conditions of crystallization and varies from large to earthy. In veins, crystalline aggregates often have a massive (confluent) structure, in which individual grains are not distinguishable by eye. Amorphous aggregates are homogeneous dense or earthy masses with a matte, waxy or low-fat sheen. Cryptocrystalline aggregates outwardly resemble amorphous ones and differ from them only microscopically.
They are colloidal systems consisting of finely dispersed crystalline particles and the medium containing them.
There are mineral formations, the composition of which does not correspond to the form that they compose - these are the so-called pseudomorphoses (Greek "pseudo" - false). They arise when chemical changes in pre-existing minerals or filling voids formed during the leaching of any mineral or organic inclusions. The former include, for example, the frequently encountered pseudomorphs of limonite after pyrite, when cubic crystals of pyrite (FeS2) turn into cryptocrystalline limonite, the latter include pseudomorphs of opal after wood, etc.
Physical properties of minerals. The constancy of the chemical composition and internal structure minerals determines their properties. Based on this various methods mineralogical studies and definitions of minerals. Most of them require special equipment and are possible only in stationary conditions. However, each researcher dealing with minerals and rocks must master the method of their field determination, based on the study of external, visible to the naked eye (macroscopically) properties.
The morphology of mineral crystals can be an important diagnostic feature, although it should be noted that in nature the same mineral under different conditions forms crystals of various shapes, and different minerals can give the same crystals. Let us note only some of the crystallographic data used below in the characterization of minerals. The whole variety of forms of mineral crystals can be divided into six large divisions, called syngonies. Not stopping at special issues, considered in the courses of crystallography, we only note that syngonies reflect the degree of symmetry of crystals. Syngonies are distinguished: cubic, uniting the most symmetrical crystals, which have several axes of symmetry of a higher order; hexagonal (with trigonal syngony), the crystals of which have one axis of the sixth or third order; tetragonal - crystals have one axis of the fourth order. The least symmetrical crystals belong to rhombic, monoclinal, or triclinic syngonies, in the crystals of which there are no higher-order symmetry axes.
Classification of minerals and their description.
The number of currently known minerals exceeds 2000. They can be grouped according to various criteria. The currently accepted classification of minerals is based on the chemical composition and structure. Much attention is also paid to genesis (Greek "genesis" - origin), which makes it possible to learn the patterns of distribution of minerals in the earth's crust. The role of various minerals in the structure of the latter is not the same: some are rare and represent only minor and optional inclusions in rocks; others make up the bulk of the rocks, determining their properties; others, forming local accumulations or scattered in rocks, are of interest as minerals. Below we consider only the most widespread minerals belonging to the classes of native elements, sulfides, halides, oxides and hydroxides, carbonates, sulfates, phosphates and silicates.
Classes of native elements and sulfides. Minerals of these classes are not rock-forming, but many of them are valuable minerals.
Of the most common minerals of the first class, one can name sulfur S, which occurs in the process of sublimation of vapors during volcanic eruptions, as well as in surface conditions during chemical changes in minerals of the sulfide and sulfate classes and by biogenic means. It is used in the chemical industry for the production of sulfuric acid, in agriculture and in a number of other industries.
Graphite C is associated mainly with the processes of metamorphism. It is widely used in metallurgy, for the production of electrodes, etc. This class includes such valuable minerals as diamond, gold, platinum, etc.
Numerous minerals - metal ores - belong to the class of sulfides.
Galena, or PbS lead sheen, is found in the form of crystalline aggregates, less often - individual crystals and their intergrowths. Syngony is cubic. Color lead grey; streak greyish-black, shining; metallic luster; opaque; cleavage perfect in three mutually perpendicular directions, i.e. parallel to the faces of the cube; hardness 2.5; density 7.5.
Sphalerite, or zinc blende ZnS, is found in the form of crystalline aggregates, less often intergrowths of cubic crystals. The color is brown, rarely colorless, with iron impurities it can be colored black; trait yellow, brown; shine diamond, metallic; shines through; cleavage perfect in six directions parallel to the faces of the rhombic dodecahedron; hardness 3.5-4; density around 4.
Deposits of galena and sphalerite, ores of lead and zinc in the USSR are numerous, for example, in the North Caucasus, in Central Asia, Transbaikalia.
One of the most common minerals of the sulfide class is pyrite FeS2. It forms aggregates of different granularity, often there are cubic crystals interspersed in rocks with hatching on their faces. Color golden yellow; streak black, greenish-black; metallic luster; the fracture is uneven; cleavage is very imperfect; hardness 6-6.5; density about 5. Used to make sulfuric acid.
The origin of minerals of the sulfide class is associated mainly with hot-water solutions (hydrothermal). They are often found in quartz veins along with many minerals of the native element class.
Class of halogen compounds. It includes minerals representing salts of fluorine-, bromide-, chloride-, hydroiodic acids. The most common minerals of this class are chlorides, which are formed mainly during the evaporation of water from surface basins. Emissions of chlorides from volcanic gases are also known.
Halite NaCl - forms dense crystalline aggregates, less often cubic crystals. Pure halite is colorless or white, often painted in various light colors; glass shine; transparent or translucent; cleavage perfect in three mutually perpendicular directions, i.e. parallel to the faces of the cube; hardness 2; density about 2. Hygroscopic, salty in taste. It is used in the food industry, in the chemical industry for the production of chlorine, sodium and their derivatives. The main deposits of the USSR are located in the Ukraine, the Urals, the Donbass and many other places.
Silvin KCl - close in origin and physical properties to halite, with which it often forms single aggregates. A distinctive feature is a bitter-salty taste. It is mainly used as a raw material for potash fertilizers, in the chemical industry.
Fluorides are associated mainly with hydrothermal, as well as magmatic and pneumatolytic processes (Greek "pneuma" - spirit, gas). Rarely formed under exogenous conditions. These include fluorite, or fluorspar - CaF2, found in the form of granular accumulations, individual crystals and their intergrowths. Syngony is cubic. The color is varied, often changing in one crystal from colorless to yellow, green, blue, violet; glass shine; cleavage perfect in four directions parallel to the faces of the octahedron; hardness 4; density 3.18. It is used in the metallurgical, chemical, ceramic industries, transparent varieties - in optics. The main deposits of the USSR in Transbaikalia and in Central Asia.
Class of oxides and hydroxides. In terms of the number of minerals included in it, it occupies one of the first places: it accounts for about 17% of the entire mass of the earth's crust. Of these, about 12.5% are silicon oxides and 3.9% are iron oxides. Minerals of this class are formed under both endogenous and exogenous conditions.
Si02 quartz is a rock-forming mineral widely distributed in the earth's crust. The basis of its structure is the silicon-oxygen tetrahedron)