During the renovation or construction of a premises, one has to deal with many controversial issues. One of the main ones is the choice of building materials. You need to evaluate the pros and cons of your preference, compare it with analogues and make a worthy decision. Mineral wool has gained enormous popularity among builders as insulation and soundproofing material.

Wall insulation means economical heating, the absence of fungi, and salvation from mold and dampness. During the summer months, good insulation prevents the walls from overheating and maintains a comfortable room temperature.

What is mineral wool?

Mineral wool is an economical insulation made from natural non-combustible materials. Its production occurs by exposing basalt fiber and metallurgical slag to high temperatures. It has good fire-fighting properties, which is especially important in the construction of houses with stove heating and in hazardous industries.

Scope of application

insulation of facades and attics;

internal wall insulation;

insulation of hot structures in production;

in the heating system, during the construction of pipelines; in the construction of flat roofs.

Such wide use is possible due to the various technical characteristics of mineral wool. It has several varieties, differing in fiber structure. Each type is distinguished by its thermal conductivity and moisture resistance.

Types of mineral wool

Glass wool

It is obtained from broken glass and small crystalline materials. Fiberglass has a good thermal conductivity coefficient - 0.030-0.052 W/m·K. The length of its fibers is from 15 to 55 mm, thickness - 5-15 microns. Working with glass wool requires extreme caution. Due to its properties, it is prickly; broken threads can penetrate the eyes and damage the skin. Therefore, gloves, goggles, and a respirator are required to work with the material. It is optimal to heat glass wool to 450 degrees, do not cool it below 60 degrees. The positive properties of glass wool are good strength and elasticity, easy installation, and the ability to trim.

Slag

The fibers of this product from blast furnace slag are about 16 mm long. The high hygroscopicity of this raw material does not allow the use of slag wool in the insulation of facades and heating mains. Most often it is used for insulation of non-residential structures. Heating temperature 250-300 degrees. In these and other properties, it is inferior to other types of mineral wool. Its main advantage is its low price, easy installation, and reliable sound insulation.

Stone wool

This is the highest quality type of mineral wool. The size of its sheets is not inferior to slag fiber. But it is not prickly, very easy to use. It has a fairly high thermal conductivity coefficient; this fiber can be heated to 1000-1500 degrees. When heated above permissible degrees, it will not burn, but only melt. When we talk about modern material for insulating houses, we mean exactly this type of wool - it is also called basalt.

Internal wall insulation

Production and properties of basalt wool

A little history:

For the first time, thin threads of volcanic rock were discovered in Hawaii. After the volcanic eruption, scientists noticed interesting finds. The hot lava flew up, and the wind pulled the rocks into thin threads, which solidified and turned into lumps similar to modern mineral wool.

Production of basalt insulation

Thanks to heat treatment at fairly high temperatures, rock materials are transformed into fibrous material. After that, binding components are added to them and put under pressure. Next, the fiber enters the polymerization chamber, where it turns into a solid product.

Basalt insulation can have a high density, which gives the product additional rigidity and good load resistance. The porous structure helps absorb impact noise. During the production process, cotton wool of various structures can be obtained. The more flexible one is used in pipelines, the semi-rigid one is used to insulate houses, and the rigid structure is indispensable in production.

Properties of basalt mineral wool:

soundproofing;

high thermal insulation;

safety;

moisture resistance;

durability;

absolutely non-flammable.

Basalt fiber is produced in rolls and slabs. It is very light and easy to cut.

Note!

Recently, the foil type of product has become very popular among builders. Thanks to the foil, an increased level of heat conservation is obtained. It is suitable for insulating any surfaces; this is the material used for ventilation and refrigeration systems.

Stamps

In factory conditions, you can obtain a product of varying densities. It is by this property that several brands of mineral wool can be distinguished.

Brand P-75

It has a density of 75 kg per cubic meter. A low-density product is used where there is no need to withstand heavy loads. For example, for insulating some roofs and attic spaces. This brand of wool is also used for heating pipes.

Attic insulation scheme

Brand P-125

With its density of 125 kg per cubic meter, it is suitable for insulating floors and interior walls. The material has good noise protection, so it is an ideal mineral wool for sound insulation.

Brand PZh-175

Material with high density and good rigidity. Indispensable where it is necessary to insulate floors made of reinforced concrete or metal.

Brand PPZh – 200

It has the highest rigidity, as indicated by the indicated abbreviation. Just like PZh-175, it is used for thermal insulation of walls made of sheet metal. But, besides this, this brand should be used where there is an increased likelihood of a fire hazard.

Facade mineral wool

Most often, mineral wool is used to insulate facades. All of the above properties of basalt fiber are significantly superior to the same polystyrene foam. It is this material that does not easily retain heat, but also helps air penetrate the walls. Particular attention should be paid to the choice of product and installation of structures.

Facade insulation

Important: It is better to purchase products in the form of slabs, which will greatly simplify their installation. The density of the material should not be less than 140 kg / cubic meter. The width of the plate itself is 10 cm.

Mineral wool and harm to health

Pessimistic sentiments that the use of mineral wool causes serious harm to health are based on the technical characteristics of past generations of mineral wool. Indeed, constant work with glass wool was very dangerous for the lungs. Today these products are used very rarely. Modern basalt fiber is produced using high-quality raw materials, paying great attention to the technological process. If all sanitary standards are observed, the binding of harmful substances - phenol and formaldehyde practically lose their negative properties for the environment.

To be sure of the safety of the material, you need to pay attention to the choice of manufacturer. If stone wool is mined by underground organizations, without complying with GOSTs and the necessary technical conditions, then there is no guarantee that the effects of phenol will not affect the health of others.

Mineral fillers such as calcium carbonate, talc, silica are very common in the polymer industry. They often, at a cost of 6-15 cents/lb, replace significantly more expensive polymers, increase the stiffness of the filled product and give the polymer greater fire resistance. The global market for plastic fillers is dominated by carbon black (carbon black) and calcium carbonate. Of the approximately 15 billion pounds of fillers in America and Europe, about half the volume is in elastomers, one-third in thermoplastics, and the rest in thermosets. About 15% of all plastics produced contain fillers.

Apart from cost, the following properties of mineral fillers are (or should be) generally considered when used as a filler in composite materials (properties are given in no particular order):

Chemical composition;

Form factor;

Density (specific gravity);

Particle size;

Particle shape;

Particle size distribution;

Particle surface area;

Ability to absorb oil;

Fire resistant properties;

Influence on the mechanical properties of the composite material;

Effect on melt viscosity;

Influence on melt shrinkage;

Thermal properties;

Color, optical properties;

Influence on fading and durability of polymers and composites;

Impact on health and safety.

Let us give some preliminary general descriptions, which will be detailed below using specific examples of mineral (and mixed) fillers.

General properties of mineral fillers

Chemical composition

Excipients can be inorganic, organic or mixed, for example Biodac, as described above. Biodac is a granular mixture of cellulose fiber, calcium carbonate and kaolin (clay). Typical inorganic fillers may be simple salts, such as calcium carbonate (CaCO 3 ) or wollastonite (CaSiO 3 ), with a precise chemical structure; complex inorganic materials such as talc [hydrated magnesium silicate, Mg 3 Si 4 O l0 (OH) 2 ] or kaolin (hydrated aluminum silicate, Al 2 O 3 -2SiO 2 -2H 2 O); or may be compounds of uncertain or variable composition, such as mica, clay and fly ash. The latter can be considered as aluminum silicate with inclusions of other elements.

Shape factor

This is the ratio of the length of a particle to its diameter. For spherical or cubic particles, the shape factor is equal to unity. For calcium carbonate particles, the shape factor is usually 1-3. For talc, the form factor is usually in the range of 5-20. For ground glass fiber it ranges from 3 to 25. For mica - 10-70. For wollastonite, its value is between 4 and 70. For chopped fiberglass, it is between 250 and 800. For natural fibers, such as cellulose, the shape factor can be from 20-80 to several thousand. The low form factor is less than 10. However, the values ​​listed are for fillers not processed in the mixer and/or extruder. After processing, the shape factor can decrease from several dozen and hundreds to 3-10.

Density (specific gravity)

Although the specific gravity of mineral fillers can vary over a wide range, the specific gravity of fillers that are used (or probably should be used) in WPC are all high, around 2.1-2.2 (fly ash) and 2.6-3 .0 g/cm 3 (calcium carbonate, talc, kaolin, mica, clay). Biodac, a granular mixture of calcium carbonate with kaolin and cellulose fiber, has a specific gravity of 1.58 g/cm 3 .

Table 1 shows how mineral fillers affect the density of filled polymers compared to wood fiber.

Table 1. Effect of the specific gravity of fillers on the density of the filled polymer. Cellulose fibers (wood flour, rice husk) usually have a specific gravity of 1.3 g/cm 3 ; calcium carbonate and talc usually have a density of 2.8 g/cm3

* Corresponding experimental data for filled polypropylene are as follows: with 20% cellulose fibers, 0.98-1.00 g/cm3; with 40% cellulose fibers, 1.08-1.10 g/cm3; with 40% calcium carbonate or talc, 1.23-1.24 g/cm3.

It can be seen that the presence of 20-40% mineral fillers significantly increases the density of filled HDPE and polypropylene compared to polymers filled with cellulose fiber.

Note. These calculations can be done as shown in the following example. For HDPE filled with 20% calcium carbonate, 100 g of filled polymer contains 20 g of CaCO 3 and 80 g of polymer. The corresponding volume fractions are 20 g/2.8 g/cm 3 = 7.1429 cm 3 for CaCO3 and 80 g/0.96 g/cm 3 = 83.3333 cm 3 for HDPE. The total volume of the filled polymer is 7.1429 cm 3 + 83.3333 cm 3 = 90.4762 cm 3. Since the mass of this sample is 100 g, the specific gravity of the filled polymer is 100 g/90.4762 cm 3 = 1.105 g/cm 3.

Note. How not to calculate the specific gravity of a composite material. A common mistake is to confuse volume and mass fractions in calculations. For example, in the above case, for HDPE filled with 20% calcium carbonate, the resulting specific gravity would be incorrect: 0.2 x 2.8 g/cm 3 + 0.8 x 0.96 g/cm 3 = 1.328 g/cm 3 . The correct answer, as we know, is 1.105 g/cm 3 (see above). It was a mistake to take volume fractions of 0.2 and 0.8 as mass fractions in the resulting composition.

Particle size

For the purposes of this discussion, fillers can be divided into coarse particles (greater than 0.1-0.3 mm, 20-150 mesh), large-size particles (about 0.1 mm or 100 µm, 150-200 mesh), medium-size particles ( about 10 µm, 250 mesh), small particles (about 1 µm), fine particles (about 0.1 µm), and nanoparticles (layered - 1 nm or 0.001 µm thick, and 200 nm or 0.2 µm long; intercalated - thickness 30 nm, length 200 nm). Nanoparticles are not considered as fillers, but rather as additives. Examples of the above particle sizes are Biodac (large particles), ground calcium carbonate (large particle size), clay (medium particle size), precipitated CaCO 3 (small particle size), some special types of silica (fine particle size), exfoliated multilayer particles organoclay. The cost of these fillers increases very significantly when moving from large and large to small and fine particles, and especially for nanoparticles. Therefore, only coarse and larger filler particles can result in cost savings in resin replacement unless the fillers impart truly beneficial properties to the composite material that justify the increased cost.

Particle Shape

This characteristic is partly, but not entirely, related to the particle aspect ratio. With the same aspect ratio of 1.0, the particles can be spherical or cubic, and spherical particles (such as carbon black, titanium dioxide, zinc oxide) improve the fluidity and reduce the melt viscosity of polymers and ensure uniform stress distribution in the hardened profile, while cubic particles (calcium hydroxide) provide good profile strengthening. Flakes (kaolin, mica, talc) facilitate the orientation of polymers. Extended particles, such as wollastonite, fiberglass and cellulose fiber, wood flour (fiber), reduce shrinkage and thermal expansion-contraction, and in particular, strengthen the monolithic material.

Particle size distribution

Particles can be monodisperse or have a specific size distribution - wide, narrow, bimodal, and so on. The distribution may not be homogeneous, and there is usually a mixture of particles of different sizes. This property of a mixture of particles largely depends on the technology of grinding and sorting (sifting) of particles. A wide distribution or bimodal distribution of mineral filler particles can be beneficial as they can provide better packing density of the particles in the matrix. Particle size distribution can affect melt viscosity.

Particle surface area

It is directly related to the “topography” of the surface and the porosity of the filler. It is measured in square meters per gram of filler and can vary from fractions of m 2 /g to hundreds of m 2 /g. For example, the specific surface area of ​​wollastonite varies from 0.4 to 5 m 2 /g, silica - from 0.8 to 3.5 m 2 /g, cellulose fiber - about 1 m 2 /g, talc - from 2.6 to 35 m 2 /g, calcium carbonate - from 5 to 24 m 2 /g, kaolin - from 8 to 65 m 2 /g, clay - from 18 to 30 m 2 /g, titanium dioxide - from 7 to 162 m 2 /g , precipitated silicon dioxide - from 12 to 800 m 2 /g. The specific surface area of ​​particles depends very much on the method used to measure area. The smaller the molecule used for measurements, the larger the specific surface area obtained per gram of material. However, when mixed with a polymer melt, the small molecular pore size of the mineral filler is unsuitable. Large open pores, on the contrary, can provide not only an adhesion area for the polymer melt, but also additional physical interaction between the filler and the polymer after it has solidified.

These two properties go hand in hand and are associated to a certain extent with the “hygroscopicity” of the filler. However, moisture content usually reflects the mass (percentage) of water per unit mass of filler under given circumstances (e.g., after or during drying), while water absorption capacity often refers to the maximum achievable moisture content or the moisture content after apparent equilibrium has been reached under ambient conditions. The moisture content of the bulk of rice husk in the summer months can be about 9.5% by weight. The moisture content of dried rice husk can be 0.2-0.5%. High moisture content in the filler causes steam to be generated during the compounding and extrusion process, which can result in high porosity (and low density) of the final extruded profile. This in turn reduces its strength and stiffness, and increases the rate of oxidation during service life, hence reducing durability.

Low moisture content in fillers is usually observed in calcium carbonate and wollastonite (0.01-0.5%), talc and aluminum trihydrate, mica (0.1-0.6%). Moderate moisture content can be observed in titanium hydroxide (up to 1.5%), clay (up to 3%), kaolin (1-2%) and Biodac (2-3%). High moisture content is often found in cellulose fiber (5-10%), wood flour (up to 12%) and fly ash (up to 20%). Biodac absorbs up to 120% of water when in direct contact with excess water.

Oil absorption capacity

This property can be useful for hydrophobic polymers such as polyolefins, since hydrophobic fillers can exhibit good interaction with the matrix. In addition, hydrophobic fillers can have a very significant effect on the viscosity of the matrix, hence its rheology and fluidity. Fillers typically absorb oil in much higher quantities compared to water. Calcium carbonate absorbs 13-21% oil, aluminum trihydrate absorbs 12-41% oil, titanium dioxide 10-45%, wollastonite 19-47%, kaolin 27-48%, talc 22-51%, mica 65-72% and wood flour 55-60%. Biodac absorbs 150% oil by weight.

Typically, if oil absorption is low, the filler does not change the melt viscosity to a large extent. Because of this, the oil absorption test is often used to characterize the effect of fillers on the rheological properties of filled polymers.

Fire resistance

“Active” flame retardants, such as aluminum trihydrate or magnesium hydroxide, cool the combustion area by releasing water above a certain temperature. Many inert fillers, such as calcium carbonate, talc, clay, fiberglass, etc., can retard flame propagation only by "eliminating fuel" for flame propagation or slowing down the release of heat. However, they do not significantly change the ignition temperature. They act rather by dissolving the fuel in a solid (polymer) phase. Calcium carbonate releases inert gases (carbon dioxide) at a temperature of about 825 °C, which is too high to dissolve the flammable gas phase, which ignites well below this temperature.

Influence on the mechanical properties of the composite material

Mineral fillers generally improve both the flexural strength and flexural modulus of filled plastics and WPC (Table 2), but the degree of improvement varies for strength and flexural modulus. The effect on bending strength is often no more than 10-20%. The effect on the flexural modulus can be as high as 200-400%, and this often depends on the particle size of the filler and its aspect ratio. The higher the filler content and aspect ratio, the greater the influence of the filler on the flexural modulus (although this does not always apply to filler content in particular).

Based on the effect of fillers on the strength of filled polymers, fillers can be divided into fillers and reinforcing fillers.

Table 2. Effect of inorganic fillers and wood flour on the flexural strength and flexural modulus of polypropylene (homopolymer)

Fillers such as wood flour, calcium carbonate, often maintain strength almost unchanged, usually within ±10% of the unfilled polymer. With reinforcing fillers such as high aspect ratio wood fibers and glass fibers, the strength of the filled polymer is always increased.

Thus, some mineral fillers increase the flexural strength of polypropylene by 30-45%, while wood flour increases the flexural strength of the same polymer by only 7-10%. The effect of fillers on the rigidity of plastics is much more pronounced, and mineral fillers increase the flexural modulus of polypropylene by up to 300%, and wood flour increases the flexural modulus of the same polymer by 150-250%.

The tensile strength of pure and filled polypropylene is approximately the same, or decreases slightly when the polymer is filled with wood flour (Table 3).

Table 3. Effect of inorganic fillers and wood fiber on the strength and tensile modulus of polypropylene (homopolymer)

Fiberglass increases the tensile strength of polypropylene by up to 15%; talc gives almost no changes; calcium carbonate and wood flour reduce the tensile strength of the same polymer by 15-30%. In relation to the tensile modulus of elasticity, its increase was up to 3.6 times (talc, fiberglass) and up to 1.6-2.6 times (wood flour, calcium carbonate).

It is difficult to predict quantitatively how the flexural strength and WPC modulus will be affected by the introduction of mineral fillers, since the properties and amount of lubricants may interfere (Table 4).

In table 4. shows that although strength and flexural modulus increase with increasing talc content compared to the same properties with wood flour, lubrication reduces the effect.

Table 4. Effect of talc on the strength and flexural modulus of wood flour-polypropylene composites in the presence of various amounts of lubricant (data provided by Luzenac America)

Effect on melt viscosity

It depends on the particle size, particle shape, aspect ratio, specific gravity of the filler and other properties of the fillers. The following example illustrates this “general” property of fillers. When polypropylene having a melt flow rate of 16.5 g/10 min was filled with a small amount of mineral and cellulose fillers, its MFI (in g/10 min) was as follows:

40% CaCO 3 15.1;

40% talc 12.2;

40% fiberglass 9.6;

20% wood (pine) flour 8.6;

40% wood flour 1.9.

Apparently, wood flour has a much greater effect on melt viscosity compared to inorganic fillers.

Effect on technological shrinkage

It obviously depends on the content of fillers (hence the polymer content) and the ability of the fillers to prevent crystallization of the polymer. The smaller the crystallites in the filled polymer, the less shrinkage. The less polymer in the filled composite, the less shrinkage. At the same content, fillers with a nucleating effect lead to less technological shrinkage. For example, if polypropylene having a process shrinkage of 1.91% was filled with a small amount of mineral filler and cellulose fiber, its process shrinkage became as follows:

40% CaCO 3 1.34%;

20% wood - fiber 0.94%;

40% talc - 0.89%;

40% wood fiber - 0.50%;

40% fiberglass -0.41%.

It can be seen that all fillers reduce process shrinkage, with wood flour showing better results compared to calcium carbonate and talc, but higher shrinkage compared to glass fiber.

Thermal properties

The thermal expansion-contraction of inorganic fillers is significantly lower compared to polymers. Therefore, the higher the filler content, the lower the expansion-compression coefficient of the composite material. Many inorganic, non-metallic fillers reduce the thermal conductivity of the composite material. For example, compared to the thermal conductivity of aluminum (204 W/deg-K-m), for talc it is 0.02, titanium dioxide 0.065, fiberglass 1 and calcium carbonate 2-3. Therefore, non-metallic mineral fillers are heat insulators rather than heat conductors. This property of fillers affects the fluidity of filled polymers and polymer-based composite materials during extrusion.

Color: optical properties

The color of fillers must be taken into account when their content is high, especially if it is necessary to produce a light-colored profile. However, composite materials usually contain enough dyes to prevent coloring by fillers, except very dark ones such as carbon black. Fillers impart opacity to the product, which is an unimportant factor in colored composite materials.

Effect on fading and durability of polymers and composites

Mineral fillers often contain impurities (such as free metals), which are catalysts for thermal and/or photo-oxidation of the filled polymer. This topic will be discussed in more detail in Chapter 15. Here we will give just two examples of fading of CaCO 3 filled HDPE and polypropylene, with 76 and 80% wt. filler, respectively. The matrix had a melt flow rate of 1 g/10 min. (HDPE) and 8 g/10 min. (polypropylene). Ashing of both filled polymers at 525 °C showed ash contents of 76.0 ± 0.1% (HDPE-CaCO 3) and 79.9 ± 0.1% (PP-CaCO 3). After 250 hours in an atmospheric chamber (Q-SUN 3000, UV filter: daylight, UV sensor: 340, 0.35 W/m2, black plate 63 °C, ASTM G155-97, cycle 1: light 1:42, light + spray 0:18) fading coefficient increased from 83.7 to 84.3 (ΔL = +0.6) [HDPE-CaCO 3 76%] and from 85.6 to 88.8 (ΔL = +3.2 ) [PP-CaCO 3 80%]. Since the calcium carbonate in this experiment was of the same origin, the increased discoloration must be attributed to the higher sensitivity of polypropylene to thermal and/or photo-oxidation in the surface layer.

Another example here showing the effect of mineral fillers on WPC oxidation (based on OI, i.e., oxidative induction time) is the durability of experimental GeoDeck decking boards made with talc and mica in addition to the conventional composition. GeoDeck without added antioxidants had a VOI of 0.50 min. In the presence of 3 and 10% talc, the VOI value was 0.51 and 0.46 minutes, respectively. In the presence of 12.5 and 28.5% mica, the VOI values ​​were 0.17 and 0.15 min, respectively. This means that in the last two examples, mica actually eliminated the oxidation resistance (albeit very low) of the composite material.

Health and Safety

Some fillers are hazardous materials and require special handling and recycling. Listed below are some fillers that are used or can be easily used in composite materials, classified according to the main parameters accepted in the industry. The indices mean: no danger, 0; slight danger, 1; moderate, 2; serious, 3; extreme danger, 4. Storage codes: general, orange; special, blue; dangerous, red.

Health: fly ash and wood flour, not classified; calcium carbonate, kaolin, 0; aluminum hydroxide, clay, fiberglass, magnesium hydroxide, mica, quartz, talc, wollastonite, 1.

Flammability:

Reactivity: fly ash and wood flour, not classified; all others listed above are 0.

Storage color code: wood flour, not classified; all others listed above are orange.

Toxicity (mg/kg): all of the above are not classified; exception - aluminum hydroxide, 150.

Carcinogenicity: all of the above are not (except for talc - if it contains asbestos).

Silicosis: calcium carbonate, clay, mica, yes; all of the above, no.

Weighted average time(TEL, average exposure over an 8-hour work shift), in mg/m 3 : talc, 2; mica, 3; fly ash, calcium carbonate, fiberglass, kaolin, silica, wood flour, 10; aluminum hydroxide, clay, magnesium hydroxide, wollastonite, not classified.

As you can see, the listed fillers are generally considered to be fairly safe, unless specifically stated so.

Minerals are natural chemical compounds or native elements found in the earth's crust. Minerals make up the rocks (soils) and soils directly under our feet. The distribution of minerals is extremely uneven. About 3000 minerals are known, only about 50 of them are widely distributed. These minerals are called rock-forming minerals. If we consider individual geological provinces, for example, the central part of the Russian Plain, then there are even fewer rock-forming minerals on the surface of the earth - about 20.

In general, there are much more chemical compounds than minerals, but most of them are substances obtained artificially. Recently, two additional classes of substances have begun to be called minerals:

• what used to be called minerals are inorganic compounds present in food products, medicines, and cosmetics;
• components formed during the production of building materials - brick, concrete, ceramics, etc.

Minerals are mostly solid, much less often liquid (groundwater) and gaseous (radon, methane). Among solid minerals, crystalline, amorphous and colloidal minerals predominate (they are less common). Minerals are very diverse in appearance and have a large number of features. The same combination of chemical elements can crystallize into different structures and form different minerals - this phenomenon is called polymorphism. For example, modifications of carbon (C) produce graphite and diamond; Iron sulfide (FS 2) forms two minerals - pyrite and marcasite, calcium carbonate CaC0 3 - the minerals calcite and aragonite.

Minerals can be isotropic or anisotropic: isotropic minerals have the same properties in all directions, while anisotropic minerals have different properties in non-parallel directions.

Based on their origin, minerals are usually divided into endogenous (deep) and exogenous (formed on the surface; these also include minerals formed on the bottom of the sea). Many minerals can be of both endogenous and exogenous origin. The factor of the presence of a mineral in the rock should not be combined with the factor of origin - many endogenous minerals further compose sedimentary (exogenous) rocks or are present in them (for example, quartz, which has an igneous or metamorphic origin, forms sands or sandy and dusty rocks). leftist fractions and is an essential component of sedimentary clayey rocks).

Mineral diagnostics

Minerals have different properties, some of which can be determined visually, others - using special equipment. Properties determined visually or using the simplest devices (hydrochloric acid, magnifying glass, knife, hardness scale) are called external, and the corresponding diagnostics are called macroscopic. Usually it is quite enough to determine the names of rock-forming minerals and the rocks composed of them and, in a preliminary, evaluative form, to judge the properties of the geological environment.

The external properties of minerals, determined macroscopically, include: form of isolation, color, powder color (line), luster, fracture, cleavage, hardness, specific gravity and some special properties.

Selection form

The most common forms are crystalline, earthy and amorphous masses. Crystals are called isometric if they are approximately equally developed in all three directions. Crystals elongated in one direction are called columnar, prismatic, needle-shaped, and crystals elongated in two directions are called tabular, lamellar, or leafy. Other forms are brushes (geodes), concretions and secretions, pseudomorphoses (fossils), oolites, etc.

One mineral can have different forms of release, while keeping other properties unchanged.

Coloring

Color - the color of the mineral. In nature there are minerals that have either one color or different colors. Graphite is always dark gray, and feldspar can range in color from white to black - pink, red, gray, green, brownish.

Powder color (trait)

Typically, the color of the mineral is darker than the color of the mineral in powder. Many colored minerals have a white powder. The powder is obtained by drawing a sample on a porcelain plate - hence the name of the property - trait. When drawing on porcelain, the result is an ideal powder, lying in a thin layer on a white background. Minerals with a hardness greater than that of porcelain (> 6.5) are said to have no characteristics. Some minerals are well diagnosed using a trait (for example, black hornblende has a dark green streak, black labradorite (feldspar) has a white or light gray streak, dark gray hematite has a cherry streak).

Forms of mineral release (schemes)

a - elongated crystals; b - flat; c - isometric; g—crystalline mass (rock); d - fossil (pseudomorphosis); e - dendrite; g - kidney-shaped sintered form; h - stalactites; and - stalagmites; k - concretion; l - secretion; m,n - oolites; o - brush (druze, geode); p - rose (rosette)

Shine

Luster is the property of minerals, like all objects, to reflect, refract, absorb rays of light, as well as our perception of reflected light. The shine of a mineral should be determined by those places where it shines brightest - on the surfaces of a fresh chip (if necessary, a chip must be obtained). One mineral may have a different luster (for example, in lamellar gypsum - glassy and pearlescent; in quartz - greasy on chips and glassy on grown edges). Let's name the types of shine, arranging them in the list as the intensity of the reflected light decreases.

• metal. Minerals are like metal objects;
• semi-metallic, diamond resin. These are bright types of glitter; minerals containing them are quite rare in nature, many are valuable minerals, but are unlikely to be encountered during work in the field of environmental management;
• fatty. The surface of the mineral gives the impression of being covered with a thin layer of oil. More often observed in minerals that have an uneven surface, for example, quartz and opal;
• pearl. Observed on flat, smooth surfaces, gives a slight color tint (examples: talc, to a lesser extent gypsum, mica);
• glass. It is observed on the smooth edges of many minerals. The entire surface shines at the same time (examples: calcite, anhydrite, feldspars);
• silky. It is observed in minerals with needle-shaped fracture, when the surface of the chip resembles long threads of shiny nylon fabric (examples: asbestos, hornblende, fibrous gypsum);
• . matte (weak, dull). The surface, even when freshly chipped, shines weakly (examples: flint, chalcedony, phosphorite in nodules);
• minerals without shine (examples: phosphorite in earthen masses, montmorillonite, kaolinite).

Kink

Fracture is the shape of the surface of a mineral resulting from breaking a sample. The fracture of one and the same sample can be described in several words, which will complement each other without contradiction. For example, the fracture of limonite is earthy and uneven at the same time, the fracture of sugar-like gypsum is granular and uneven throughout the entire sample and stepped, if you look closely at the crystals. Some types of fracture that can be depicted schematically are presented below.

Some types of fracture (schemes)

a - stepped in the crystal; b - stepped in the crystalline mass; c - needle-shaped in a crystalline mass; g - coarse-grained; d - conchoidal

Types of fracture:

• stepped. Easily determined in single crystals that have fracture planes, for example, in calcite and mica. It is more difficult to see the stepwise fracture of crystals inside crystalline masses. In such cases, you should find the crystals and pay attention to the small planes in them, while the entire sample will give the impression of being uneven or granular, such as labradorite or dolomite;
• needle-shaped (splintery, fibrous). Looks like a break in wood or some fibrous material; observed in hornblende, asbestos;
• granular (sugar-like). Observed in minerals with a fine-crystalline form of precipitation; the crystals are still visible, but their fracture is already poorly visible (examples: anhydrite, fine-crystalline apatite);
• earthy. It is observed in minerals with a non-smooth surface, in which the crystals are not visible due to their small size. Samples look like dry earth, have no shine, and often stain your hands (examples: limonite, phosphorite, clay minerals);
• conchoidal. More often observed in amorphous minerals. The fracture surfaces are shiny, convex or concave, smooth,
  with sharp edges, which was used by ancient people in the manufacture of tools and weapons (examples: flint, chalcedony, obsidian, quartz);
• uneven. When split, a mineral forms irregular, irregular surfaces (examples: fine-crystalline quartz, phosphorite).

Cleavage

Cleavage is the ability of crystalline minerals to split along specific directions of the crystal lattice. This property is not observed in objects that surround us in everyday life. Due to cleavage, when minerals are split, planes, needles or fibers can form. Most crystalline minerals have cleavage and amorphous minerals cannot. Cleavage surfaces should not be confused with the faces formed during crystal growth. Cleavage is clearly visible in large crystals (example: mica or feldspar). In broken samples of coarse-crystalline masses, cleavage is determined already because the crystals themselves are visible - each has given its own plane, different from the neighboring one.

Cleavage scheme

a - a large crystal will split only along cracks parallel to the edges; b - chips running along the cleavage planes are clearly visible in the crystalline mass

Cleavage varies. It can appear very well, like in mica, or absent, like in quartz crystals. According to the degree of perfection, there are five types of cleavage: very perfect, perfect, average, imperfect, very imperfect (there is actually no cleavage). If there is no cleavage, it is often impossible to understand where one crystal ended and the next began. Cleavage is not at all visible in minerals represented by earthy masses. In this case, it is determined under a microscope, and the data is published. Due to the anisotropy of crystals, even within the same mineral, cleavage can manifest itself in different ways; for example, feldspar has perfect cleavage in two directions and average cleavage in the third. Micas have very perfect cleavage in one direction and do not have it in the other two.

mica crystal

There is cleavage in one direction, there is no cleavage in the other two directions, the mica is torn like a sheet of paper. Overgrown faces are not taken into account.

As can be understood from the above, cleavage is quite closely related to fracture. It is present in minerals with stepwise, acicular and coarse-grained fractures and is absent in minerals with conchoidal fractures. You should read about the cleavage of minerals with fine-grained, earthy, uneven fractures in reference books.

Density (specific gravity)

It is determined by eye. Most minerals have a density of 2.5-3.5 g/cm 3 . Density helps to recognize light rocks - tripoli, opoka, diatomite, dried clay, since they have a density of less than 2.0 g/cm 3 , while heavy minerals have a density of more than 4 g/cm 3 .

Hardness

Hardness is the resistance of the surface of a material to scratching, cutting, indentation, and abrasion. This is a very convenient property for simple diagnostics of minerals. Minerals have constant hardness. You can always try to scratch the sample with your fingernail,

knife, piece of glass. You can also scratch other materials with the sharp corner of the sample.

In geological practice, in the simplest diagnostics, it is customary to compare the sample in question with standard minerals by scratching them against each other. The scale of the German geologist Friedrich Mohs is used as a standard. The scale in conventional units ranges from 1 to 10.

Mineral hardness

Mohs scale			hardness	Substitutes for the Mohs scale
Hardness		Mineral		Materials	Hardness replace calf
Relate- body	kg/cm 2
		Talc	Soft	Soft pencil
		Gypsum		Nail	2,0-2,5
		Calcite		Bronze coin	2,5-4,0
		Fluorite		Iron nail	4,0-4,5
		Apatite		Glass
		Feldspar (microcline, orthoclase, albite, anorthitis)	Solid	Plain steel, razor blade	5,0-6,0
	1120	Quartz		Tool steel	7,0-7,5
	1427	Topaz	Very hard
	2060	Corundum
	10 060	Diamond

Using the Mohs scale, it is possible to measure the hardness of minerals with an accuracy of 0.5 or 1. The result obtained is announced, for example, as follows: dolomite has a hardness of 3.5.

Special properties. This includes unusual properties found only in certain minerals.

1. Reaction with acids. Calcite, dolomite and other carbonates enter it: CaC0 3 (calcite) + 2HC1 (hydrochloric acid) -> CaC1 2 + H 2 0 + C0 2.
2. Odor when rubbed. Phosphorite may have it.
3. The salty taste is halite (NaCl), the bitter taste is sylvin (KS1).
4. Perception by touch. Talc and kaolinite can be greasy and slippery.
5. Iridescence is the appearance of a beautiful blue reflection on the cleavage chips of Labradorite.
6. Magneticity. It is checked by the reaction of the compass needle. Some minerals containing iron, cobalt, and nickel have it.
7. Birefringence. Some transparent minerals split the image. It is clearly visible if you place such a sample on the text and look through it.

Minerals are chemical compounds (with the exception of native elements). However, even colorless, optically transparent samples of these minerals almost always contain small amounts of impurities.

Natural solutions or melts from which minerals crystallize usually consist of many elements. During the formation of compounds, a few atoms of less common elements can replace atoms of the main elements. Such substitution is so common that the chemical composition of many minerals only very rarely approaches that of the pure compound.

For example, the composition of the common rock-forming mineral olivine varies within the compositions of two so-called. end members of the series: from forsterite, magnesium silicate Mg2SiO4, to fayalite, iron silicate Fe2SiO4. The ratio of Mg:Si:O in the first mineral and Fe:Si:O in the second is 2:1:4.

In olivines of intermediate composition, the ratios are the same, i.e. (Mg + Fe):Si:O is 2:1:4, and the formula is written as (Mg,Fe)2SiO4. If the relative amounts of magnesium and iron are known, then this can be reflected in the formula (Mg0.80Fe0.20)2SiO4, from which it can be seen that 80% of the metal atoms are represented by magnesium, and 20% by iron.

Structure. All minerals, with the exception of water (which, unlike ice, is not usually classified as minerals) and mercury, are solids at ordinary temperatures. However, if water and mercury are greatly cooled, they solidify: water at 0 ° C, and mercury at -39 ° C. At these temperatures, water molecules and mercury atoms form a characteristic regular three-dimensional crystalline structure (the terms “crystalline” and “solid”) " in this case are almost equivalent).

Thus, minerals are crystalline substances whose properties are determined by the geometric arrangement of their constituent atoms and the type of chemical bond between them. The unit cell (the smallest subdivision of a crystal) is made up of regularly arranged atoms held together by electronic bonds.

These tiny cells, endlessly repeating in three-dimensional space, form a crystal. The sizes of unit cells in different minerals are different and depend on the size, number and relative arrangement of atoms within the cell. Cell parameters are expressed in angstroms or nanometers (1 = 10 -8 cm = 0.1 nm).

The elementary cells of a crystal put together tightly, without gaps, fill the volume and form a crystal lattice. Crystals are divided based on the symmetry of the unit cell, which is characterized by the relationship between its edges and corners.

Usually there are 7 systems (in order of increasing symmetry): triclinic, monoclinic, rhombic, tetragonal, trigonal, hexagonal and cubic (isometric). Sometimes trigonal and hexagonal systems are not separated and are described together under the name hexagonal system.

Syngonies are divided into 32 crystal classes (types of symmetry), including 230 space groups. These groups were first identified in 1890 by the Russian scientist E.S. Fedorov. Using X-ray diffraction analysis, the dimensions of the unit cell of a mineral, its syngony, symmetry class and space group are determined, and the crystal structure is deciphered, i.e. the relative position in three-dimensional space of the atoms that make up the unit cell.

GEOMETRIC (MORPHOLOGICAL) CRYSTALLOGRAPHY

Crystals with their flat, smooth, shiny edges have long attracted human attention. Since the advent of mineralogy as a science, crystallography has become the basis for the study of the morphology and structure of minerals. It was found that the faces of crystals have a symmetrical arrangement, which allows the crystal to be assigned to a certain system, and sometimes to one of the classes (symmetry) (see above).

X-ray studies have shown that the external symmetry of crystals corresponds to the internal regular arrangement of atoms. The sizes of mineral crystals vary over a very wide range - from giants weighing 5 tons (the mass of a well-formed quartz crystal from Brazil) to so small that their faces can only be distinguished under an electron microscope.

The crystal shape of even the same mineral may differ slightly in different samples; for example, quartz crystals are almost isometric, acicular or flattened. However, all quartz crystals, large and small, pointed and flat, are formed by the repetition of identical unit cells.

If these cells are oriented in a certain direction, the crystal has an elongated shape; if in two directions to the detriment of the third, then the shape of the crystal is tabular. Since the angles between the corresponding faces of the same crystal have a constant value and are specific to each mineral type, this feature is necessarily included in the characteristics of the mineral.

Minerals represented by individual well-cut crystals are rare. Much more often they occur in the form of irregular grains or crystalline aggregates. Often a mineral is characterized by a certain type of aggregate, which can serve as a diagnostic feature. There are several types of units.

Dendritic branching aggregates similar to fern leaves or moss and characteristic, for example, of pyrolusite. Fibrous aggregates consisting of densely packed parallel fibers are typical of chrysotile and amphibole asbestos.

Collomorphic aggregates, having a smooth rounded surface, are built from fibers that extend radially from a common center. Large round masses are mastoid (malachite), while smaller ones are kidney-shaped (hematite) or grape-shaped (psilomelane).

Scaly aggregates, consisting of small plate-like crystals, are characteristic of mica and barite.

Stalactites- drip-drip formations hanging in the form of icicles, tubes, cones or “curtains” in karst caves. They arise as a result of the evaporation of mineralized water seeping through limestone cracks, and are often composed of calcite (calcium carbonate) or aragonite.

Oolites- aggregates consisting of small balls and resembling fish eggs are found in some calcite (oolitic limestone), goethite (oolitic iron ore) and other similar formations.

After accumulating x-ray data and comparing them with the results of chemical analyses, it became obvious that the features of the crystal structure of a mineral depend on its chemical composition. Thus, the foundations of a new science—crystal chemistry—were laid.

Many seemingly unrelated properties of minerals can be explained by taking into account their crystal structure and chemical composition. Some chemical elements (gold, silver, copper) are found in native, i.e. pure, form. They are built from electrically neutral atoms (unlike most minerals, whose atoms carry an electrical charge and are called ions). An atom with a lack of electrons is positively charged and is called a cation; an atom with an excess of electrons has a negative charge and is called an anion.

The attraction between oppositely charged ions is called ionic bonding and serves as the main binding force in minerals. With another type of bond, outer electrons rotate around the nuclei in common orbits, connecting the atoms to each other. A covalent bond is the strongest type of bond.

Minerals with covalent bonds usually have high hardness and melting points (for example, diamond). A much smaller role in minerals is played by the weak van der Waals bond that occurs between electrically neutral structural units.

The binding energy of such structural units (layers or groups of atoms) is distributed unevenly. Van der Waals bonds provide attraction between oppositely charged regions in larger structural units. This type of bond is observed between layers of graphite (one of the natural forms of carbon), formed due to the strong covalent bond of carbon atoms. Due to the weak bonds between the layers, graphite has low hardness and very perfect cleavage, parallel to the layers. Therefore, graphite is used as a lubricant.

Oppositely charged ions approach each other to a distance at which the repulsive force balances the attractive force. For any particular cation-anion pair, this critical distance is equal to the sum of the “radii” of the two ions. By determining the critical distances between different ions, it was possible to determine the size of the radii of most ions (in nanometers, nm). Since most minerals are characterized by ionic bonds, their structures can be visualized in the form of touching balls.

The structures of ionic crystals depend mainly on the magnitude and sign of the charge and the relative sizes of the ions. Since the crystal as a whole is electrically neutral, the sum of the positive charges of the ions must be equal to the sum of the negative ones. In sodium chloride (NaCl, the mineral halite), each sodium ion has a charge of +1, and each chloride ion -1 (Fig. 1), i.e. Each sodium ion corresponds to one chlorine ion. However, in fluorite (calcium fluoride, CaF2), each calcium ion has a charge of +2, and each fluoride ion has a charge of -1. Therefore, to maintain the overall electrical neutrality of fluorine ions, it must be twice as much as calcium ions (Fig. 2).

The possibility of their inclusion in a given crystal structure also depends on the size of the ions. If the ions are the same size and are packed in such a way that each ion touches 12 others, then they are in appropriate coordination.

There are two ways of packing spheres of the same size (Fig. 3): cubic close packing, which generally leads to the formation of isometric crystals, and hexagonal close packing, which forms hexagonal crystals. As a rule, cations are smaller in size than anions, and their sizes are expressed in fractions of the anion radius, taken as one.

Typically the ratio obtained by dividing the radius of the cation by the radius of the anion is used. If a cation is only slightly smaller than the anions with which it combines, it can be in contact with the eight anions surrounding it, or, as is commonly said, in eight-fold coordination with respect to the anions, which are located, as it were, at the vertices of a cube around it. This coordination (also called cubic) is stable at ionic radius ratios from 1 to 0.732 (Fig. 4a).

At a smaller ionic radius ratio, eight anions cannot be stacked to touch the cation. In such cases, the packaging geometry allows six-fold coordination of cations with anions located at six vertices of the octahedron (Fig. 4b), which will be stable at ratios of their radii from 0.732 to 0.416.

With a further decrease in the relative size of the cation, a transition occurs to quadruple, or tetrahedral, coordination, stable at radius ratios from 0.414 to 0.225 (Fig. 4c), then to triple coordination within radius ratios from 0.225 to 0.155 (Fig. 4c). d) and double - with radius ratios less than 0.155 (Fig. 4e).

Although other factors also determine the type of coordination polyhedron, for most minerals the ionic radius ratio principle is one effective means of predicting crystal structure.

Rice. 4. COORDINATION POLYHEDRON are formed when anions are placed around cations. The possible types of arrangement depend on the relative sizes of the anions and cations. The following types of coordination are distinguished: a - cubic, or eight-fold coordination; b - octahedral, or sixfold; c - tetrahedral, or quadruple; g - triangular or triple coordination; d - double coordination.

Minerals of completely different chemical compositions can have similar structures that can be described using the same coordination polyhedra. For example, in sodium chloride NaCl, the ratio of the radius of the sodium ion to the radius of the chlorine ion is 0.535, indicating octahedral, or six-fold, coordination.

If six anions cluster around each cation, then to maintain a 1:1 cation to anion ratio, there must be six cations around each anion. This produces a cubic structure known as the sodium chloride type structure.

Although the ionic radii of lead and sulfur differ sharply from the ionic radii of sodium and chlorine, their ratio also determines the sixfold coordination, therefore PbS galena has a sodium chloride-type structure, i.e., halite and galena are isostructural.

Impurities in minerals are usually present in the form of ions that replace those of the host mineral. Such substitutions greatly affect the sizes of ions. If the radii of two ions are equal or differ by less than 15%, they are easily substituted. If this difference is 15-30%, such substitution is limited; with a difference of more than 30%, substitution is practically impossible.

There are many examples of pairs of isostructural minerals with similar chemical compositions between which ion substitution occurs. Thus, the carbonates siderite (FeCO3) and rhodochrosite (MnCO3) have similar structures, and iron and manganese can replace each other in any ratio, forming the so-called. solid solutions. There is a continuous series of solid solutions between these two minerals. In other pairs of minerals, ions have limited possibilities for mutual substitution.

Since minerals are electrically neutral, the charge of the ions also affects their mutual substitution. If substitution occurs with an oppositely charged ion, then a second substitution must take place in some part of this structure, in which the charge of the substituting ion compensates for the violation of electrical neutrality caused by the first. Such conjugate substitution is observed in feldspars - plagioclases, when calcium (Ca2+) replaces sodium (Na+) with the formation of a continuous series of solid solutions.

The excess positive charge resulting from the replacement of the Na+ ion by the Ca2+ ion is compensated by the simultaneous replacement of silicon (Si4+) with aluminum (Al3+) in adjacent areas of the structure.

PHYSICAL PROPERTIES OF MINERALS

Although the main characteristics of minerals (chemical composition and internal crystal structure) are established on the basis of chemical analyzes and X-ray diffraction, they are indirectly reflected in properties that are easily observed or measured. To diagnose most minerals, it is enough to determine their luster, color, cleavage, hardness, and density.

Shine- qualitative characteristic of light reflected by a mineral. Some opaque minerals reflect light strongly and have a metallic luster. This is common in ore minerals such as galena (lead mineral), chalcopyrite and bornite (copper minerals), argentite and acanthite (silver minerals).

Most minerals absorb or transmit a significant portion of the light falling on them and have a non-metallic luster. Some minerals have a luster that transitions from metallic to non-metallic, which is called semi-metallic.

Minerals with a non-metallic luster are usually light-colored, some of them are transparent. Quartz, gypsum and light mica are often transparent. Other minerals (for example, milky white quartz) that transmit light, but through which objects cannot be clearly distinguished, are called translucent. Minerals containing metals differ from others in light transmission.

If light passes through a mineral, at least in the thinnest edges of the grains, then it is, as a rule, non-metallic; if the light does not pass through, then it is ore. There are, however, exceptions: for example, light-colored sphalerite (zinc mineral) or cinnabar (mercury mineral) are often transparent or translucent.

Minerals differ in the qualitative characteristics of their non-metallic luster. The clay has a dull, earthy sheen. Quartz on the edges of crystals or on fracture surfaces is glassy, ​​talc, which is divided into thin leaves along the cleavage planes, is mother-of-pearl. Bright, sparkling, like a diamond, shine is called diamond.

When light falls on a mineral with a non-metallic luster, it is partially reflected from the surface of the mineral and partially refracted at this boundary. Each substance is characterized by a certain refractive index. Because it can be measured with high precision, it is a very useful mineral diagnostic feature.

The nature of the luster depends on the refractive index, and both of them depend on the chemical composition and crystal structure of the mineral. In general, transparent minerals containing heavy metal atoms are characterized by high luster and a high refractive index. This group includes such common minerals as anglesite (lead sulfate), cassiterite (tin oxide) and titanite or sphene (calcium titanium silicate).

Minerals composed of relatively light elements can also have high luster and a high refractive index if their atoms are tightly packed and held together by strong chemical bonds. A striking example is diamond, which consists of only one light element, carbon.

To a lesser extent, this is true for the mineral corundum (Al2O3), the transparent colored varieties of which - ruby ​​and sapphires - are precious stones. Although corundum is composed of light atoms of aluminum and oxygen, they are so tightly bound together that the mineral has a fairly strong luster and a relatively high refractive index.

Some glosses (oily, waxy, matte, silky, etc.) depend on the state of the surface of the mineral or on the structure of the mineral aggregate; a resinous luster is characteristic of many amorphous substances (including minerals containing the radioactive elements uranium or thorium).

Color- a simple and convenient diagnostic sign. Examples include brass-yellow pyrite (FeS2), lead-gray galena (PbS) and silvery-white arsenopyrite (FeAsS2). In other ore minerals with a metallic or semi-metallic luster, the characteristic color may be masked by the play of light in a thin surface film (tarnish). This is common to most copper minerals, especially bornite, which is called "peacock ore" because of its iridescent blue-green tarnish that quickly develops when freshly fractured. However, other copper minerals are painted in familiar colors: malachite - green, azurite - blue.

Some non-metallic minerals are unmistakably recognizable by the color determined by the main chemical element (yellow - sulfur and black - dark gray - graphite, etc.). Many non-metallic minerals consist of elements that do not provide them with a specific color, but they have colored varieties, the color of which is due to the presence of impurities of chemical elements in small quantities that are not comparable with the intensity of the color they cause. Such elements are called chromophores; their ions are characterized by selective absorption of light. For example, the deep purple amethyst owes its color to a trace amount of iron in quartz, while the deep green color of emerald is due to the small amount of chromium in beryl.

Colors in normally colorless minerals can result from defects in the crystal structure (caused by unfilled atomic positions in the lattice or the incorporation of foreign ions), which can cause selective absorption of certain wavelengths in the white light spectrum. Then the minerals are painted in additional colors. Rubies, sapphires and alexandrites owe their color to precisely these light effects.

Colorless minerals can be colored by mechanical inclusions. Thus, thin scattered dissemination of hematite gives quartz a red color, chlorite - green. Milky quartz is clouded with gas-liquid inclusions. Although mineral color is one of the most easily determined properties in mineral diagnostics, it must be used with caution as it depends on many factors.

Despite the variability in the color of many minerals, the color of the mineral powder is very constant, and therefore is an important diagnostic feature. Typically, the color of a mineral powder is determined by the line (the so-called “line color”) that the mineral leaves when it is passed over an unglazed porcelain plate (biscuit). For example, the mineral fluorite comes in different colors, but its streak is always white.

Cleavage. A characteristic property of minerals is their behavior when splitting. For example, quartz and tourmaline, whose fracture surface resembles a glass chip, have a conchoidal fracture. In other minerals, the fracture may be described as rough, jagged, or splintered.

For many minerals, the characteristic is not fracture, but cleavage. This means that they cleave along smooth planes directly related to their crystal structure. The bonding forces between the planes of the crystal lattice can vary depending on the crystallographic direction.

If they are much larger in some directions than in others, then the mineral will split across the weakest bond. Since cleavage is always parallel to the atomic planes, it can be designated by indicating crystallographic directions. For example, halite (NaCl) has cube cleavage, i.e. three mutually perpendicular directions of possible split.

Cleavage is also characterized by the ease of manifestation and the quality of the resulting cleavage surface. Mica has very perfect cleavage in one direction, i.e. easily splits into very thin leaves with a smooth shiny surface. Topaz has perfect cleavage in one direction.

Minerals can have two, three, four or six cleavage directions along which they are equally easy to split, or several cleavage directions of varying degrees. Some minerals have no cleavage at all. Since cleavage, as a manifestation of the internal structure of minerals, is their constant property, it serves as an important diagnostic feature.

Hardness- the resistance that the mineral provides when scratched. Hardness depends on the crystal structure: the more tightly the atoms in the structure of a mineral are connected to each other, the more difficult it is to scratch it. Talc and graphite are soft plate-like minerals, built from layers of atoms held together by very weak forces. They are greasy to the touch: when rubbed against the skin of the hand, individual thin layers slip off. The hardest mineral is diamond, in which the carbon atoms are so tightly bonded that it can only be scratched by another diamond.

At the beginning of the 19th century. Austrian mineralogist F. Moos arranged 10 minerals in increasing order of their hardness. Since then, they have been used as standards for the relative hardness of minerals, the so-called. Mohs scale.

MOH HARDNESS SCALE

To determine the hardness of a mineral, it is necessary to identify the hardest mineral that it can scratch. The hardness of the mineral being examined will be greater than the hardness of the mineral it scratched, but less than the hardness of the next mineral on the Mohs scale.

Mineral	Relative hardness
Orthoclase

To quickly determine hardness, you can use the following, simpler, practical scale.

Bonding forces can vary depending on the crystallographic direction, and since hardness is a rough estimate of these forces, it can vary in different directions. This difference is usually small, with the exception of kyanite, which has a hardness of 5 in the direction parallel to the length of the crystal and 7 in the transverse direction. In mineralogical practice, the measurement of absolute hardness values ​​(so-called microhardness) using a sclerometer device, which is expressed in kg/mm ​​2, is also used.

Density. The mass of atoms of chemical elements varies from hydrogen (the lightest) to uranium (the heaviest). All other things being equal, the mass of a substance consisting of heavy atoms is greater than that of a substance consisting of light atoms. For example, two carbonates - aragonite and cerussite - have a similar internal structure, but aragonite contains light calcium atoms, and cerussite contains heavy lead atoms. As a result, the mass of cerussite exceeds the mass of aragonite of the same volume.

Mass per unit volume of mineral also depends on the packing density of atoms. Calcite, like aragonite, is calcium carbonate, but in calcite the atoms are less densely packed, so it has less mass per unit volume than aragonite. The relative mass, or density, depends on the chemical composition and internal structure.

Density is the ratio of the mass of a substance to the mass of the same volume of water at 4° C. So, if the mass of a mineral is 4 g, and the mass of the same volume of water is 1 g, then the density of the mineral is 4. In mineralogy, it is customary to express density in g/cm3 .

Density is an important diagnostic feature of minerals and is not difficult to measure. First, the sample is weighed in air and then in water. Since a sample immersed in water is subject to an upward buoyant force, its weight there is less than in air. The weight loss is equal to the weight of water displaced. Thus, density is determined by the ratio of the mass of a sample in air to its weight loss in water.

Pyro-electricity. Some minerals, such as tourmaline, calamine, etc., become electrified when heated or cooled. This phenomenon can be observed by pollinating a cooling mineral with a mixture of red lead and sulfur powders. In this case, sulfur covers positively charged areas of the mineral surface, and minium covers areas with a negative charge.

Magneticity – This is the property of some minerals to act on a magnetic needle or be attracted by a magnet. To determine magnetism, use a magnetic needle placed on a sharp tripod, or a magnetic shoe or bar. It is also very convenient to use a magnetic needle or knife.

When testing for magnetism, three cases are possible:

a) when a mineral in its natural form (“by itself”) acts on a magnetic needle,

b) when the mineral becomes magnetic only after calcination in the reducing flame of a blowpipe

c) when the mineral does not exhibit magnetism either before or after calcination in a reducing flame. To calcinate with a reducing flame, you need to take small pieces of 2-3 mm in size.

Glow. Many minerals that do not glow on their own begin to glow under certain special conditions (when heated, exposed to X-rays, ultraviolet and cathode rays, when broken, scratched, etc.).

There are phosphorescence, luminescence, thermoluminescence and triboluminescence of minerals.

Phosphorescence is the ability of a mineral to glow after exposure to one or another ray (willite).

Luminescence is the ability to glow at the moment of irradiation (scheelite when irradiated with ultraviolet and cathode rays, calcite, etc.).

Thermoluminescence - glow when heated (fluorite, apatite).

Triboluminescence - glow at the moment of scratching with a needle or splitting (mica, corundum).

Radioactivity. Many minerals containing elements such as niobium, tantalum, zirconium, rare earths, uranium, and thorium often have quite significant radioactivity, easily detectable even by household radiometers, which can serve as an important diagnostic sign. To test for radioactivity, the background value is first measured and recorded, then the mineral is brought, possibly closer to the detector of the device. An increase in readings of more than 10-15% can serve as an indicator of the radioactivity of the mineral.

Electrical conductivity. A number of minerals have significant electrical conductivity, which allows them to be clearly distinguished from similar minerals. Can be checked with a regular household tester.

MINERALS IDENTIFICATION

INTRODUCTION

This manual is intended to assist students studying a short course in engineering geology in their independent work on the identification of minerals. The determinant is compiled in the form of a table, which simplifies the selection of a mineral that corresponds to a set of properties determined by the student. The properties of minerals and characteristics of classification groups are given in special sections.

1. Determination of the brilliance of a mineral.

2. Determination of hardness.

3. Determining the color of the line.

4. Selection of suitable minerals according to the vertical graphs of certain properties of points 1, 2, 3.

5. Identification by determining other properties along the horizontal lines of the determinant.

At the end of the manual there is an alphabetical index of the 116 minerals described in it and their formulas are given.

I. PROPERTIES AND GENESIS OF MINERALS

Basic properties of minerals

Minerals are relatively specific and fairly stable chemical compounds and native elements, characterized by a strictly constant internal structure. Typically, minerals include natural formations that arise as a result of physical and chemical processes in the depths and on the surface of the earth’s crust. However, these include precious stones grown in laboratories and factories, mineral formations obtained by modeling geological processes, and pearls grown as aquaculture.

Today, up to 4,000 minerals are known. Of course, there are different taxonomies of them. The manual uses a principle based on the identification of classes, subclasses, and groups of fractional chemical classification units. Division based on chemical constitution reflects many properties of minerals that allow them to be diagnosed. The determinant shows the basic properties of the most typical representatives of native elements, sulfides, sulfates, halogens, fluorides, phosphates, carbonates, oxides and silicates.

The basic properties are inherent in all minerals, so diagnosis is based on differences in the characteristics of these characteristics. In addition, diagnostics is helped by additional signs that reflect specific properties that are not inherent in all, and even unique, minerals, but allow them to be quickly and unambiguously identified. The determinant takes into account both basic (chemistry, structure, mineral aggregates, hardness, density, cleavage, fracture, color, feature, luster, genesis) and additional (magnetic and electrical properties, hygroscopicity, smell, taste, flammability, elasticity, malleability , radioactivity) properties and provides information regarding the practical use of minerals.

The structure of minerals. In nature, there are solid, liquid and gaseous mineral formations. Solid minerals can be crystalline and amorphous. Crystalline ones consist of many identical structural elements that form an ordered spatial (crystalline) lattice. There are atomic, ionic and molecular types of lattices that determine anisotropy(different properties), isotropy (same properties) of crystals and their ability to self-cut. Crystals - both natural and artificial - have the shape of polyhedra. They can be isotropic or anisotropic. Amorphous minerals are always isotropic. The ability of substances with the same chemical composition to crystallize in different forms is called polymorphism (multiformity). For example: diamond and graphite, pyrite and marcasite, calcite and aragonite. The different structures of polymorphic varieties explain their different properties. Some substances of different chemical compositions can form similar crystallographic forms. Such substances can create mixed forms containing the original components in different proportions. This phenomenon is called isomorphism, and the mixtures are called isomorphic. An example is feldspars, an isomorphic series of which is formed by mixing albite and anorthite molecules.

Under natural conditions, crystalline forms that are not quite regular and have some defects most often grow, but despite any defects, the angles between the corresponding faces of crystals of the same substance remain the same and constant. This law of constancy of facet angles makes it possible to establish the ideal shape of crystals and accurately diagnose the smallest mineral grains.

Different degrees of symmetry of crystals are explained by different combinations of planes, center axes and symmetry in them. There can be 32 such combinations, and they are called classes(or types of) symmetry. The latter are combined into 7 systems, or syngonies: cubic, tetragonal, hexagonal, rhombic, trigonal, monoclinic and triclinic. Cubic crystals have highest symmetry: their simplest element is a cube, they are isotropic. Crystals of hexagonal, tetragonal and trigonal systems are characterized by average symmetry. They have columnar, columnar, acicular, leafy, tabular, lamellar habit(shape) and six-, four- and three-sided sections (respectively), perpendicular to the long axis. Anisotropy is expressed in the difference in the main properties along the long and short axes. Orthorhombic, monoclinic and triclinic systems belong to inferior symmetry group. They are characterized by very diverse shapes with anisotropic properties. Orthorhombic crystals have a cross-section perpendicular to the long axis, which is shaped like a rhombus.

Natural mineral forms (clusters). Natural accumulations of mineral grains, or crystals, are commonly called mineral aggregates. They can be mono- and polymineral, those. consist of one or more minerals. The shape of mineral aggregates depends on their composition and formation conditions.

A group of crystals grown on a common base forms druz. A drusen with small fused crystals oriented in one direction is called with a brush. These forms are formed during the crystallization of minerals in the voids of rocks (quartz, calcite, gypsum). Have the same genesis secretion– mineral formations that partially or completely fill cavities and grow from the periphery to the center. Secretions can form both amorphous (chalcedony) and crystalline (quartz, calcite) minerals. Large secretions are called geodes, small – tonsils.

Nodular formations that arose in loose sedimentary formations at the bottom of ancient and modern reservoirs as a result of the accumulation of mineral matter around foreign centers of crystallization are called nodules. Nodules grow from the center to the periphery; their structure can be radial or concentric. Their shapes and sizes are very different. The smallest nodules are oolites (calcite, aragonite, phosphorite, flint, siderite, ferromanganese nodules of the modern ocean floor).

In voids, including caves, sinter forms are widespread. They can have a wide variety of sizes and compositions (calcite, malachite, clay minerals, ice, etc.). This is first of all stalactites, stalagmites and stalagnates, kidney-shaped and grape-shaped cave formations.

With the rapid crystallization of salts falling from groundwater in small cracks and clay, thin branched tree-like formations are formed - dendrites. The most commonly found are dendrites of native copper, ferrous and manganese compounds, etc.

Mineral aggregates of disordered grains and crystals are divided into coarse-grained (more than 3 mm), medium-grained (1–3 mm) and fine-grained (less than 1 mm). Their appearance can be not only granular (crystalline), but also lamellar, leafy, columnar, banded, fibrous, oolitic, etc. It is the nature of mineral aggregates that determines the structural and textural characteristics of rocks. Aggregates of grains indistinguishable under a magnifying glass are called cryptocrystalline; soft, dirty hands, reminiscent of loose soil - earthy(kaolin, bauxite, limonite, etc.).

False forms that do not correspond to the true habit of the substance composing them are called pseudomorphoses. In accordance with genesis, pseudomorphoses of transformation are distinguished, or metamorphosis, such as the formation of limonite from pyrite; displacement (chalcedony, flint on calcite), execution (opal, limonite on wood).

Physical properties of minerals determine a set of its main characteristics, which should include: hardness, density, cleavage, fracture, color, line, shine.

Hardness, or fracture resistance during diagnostics is determined by scratching one mineral with another. In this way, they find out which mineral is harder, i.e. determine relative hardness. Determinations are made on a 10-point F. Mohs scale, consisting of 10 minerals, in which each subsequent mineral is one point harder than the previous one and therefore scratches it. Below is the F. Mohs scale with some practical recommendations.

1. Talc (scrape off with a fingernail).

2. Plaster (scratched with a fingernail).

3. Calcite (scrape off with a knife).

4. Fluorite (easily scratched with a knife).

5. Apatite (difficult to scratch with a knife).

6. Orthoclase (hard to be scratched by glass).

7. Quartz, (not scratched by glass).

8. Topaz, (leaves a scratch on the knife and glass).

9. Corundum, (leaves a scratch on the knife and glass).

10. Diamond, (leaves a scratch on the knife and glass).

When determining hardness, do not confuse a scratch with a line. The dust of the rock is wiped off the line without a trace with a finger. It must be remembered that anisotropic minerals have different hardness in different directions, and cryptocrystalline, porous and powdery masses are always softer than well-cut crystals (hematite ocher - 1, hematite crystal - 6).

Density (specific gravity)– always reflects the chemical composition and structure of the mineral. It is determined approximately by “weighing” the mineral in the palm of your hand. Usually there are three weight categories: light (up to 3 g/cm3), medium (3–4 g/cm3) and heavy (more than 4 g/cm3) minerals. With a specific gravity of more than 10 g/cm, they speak of very heavy minerals. These include native gold, silver, platinum, and mercury. The heaviest mineral known on Earth is osmic iridium, which has a density of 23 g/cm 3 . Most of the minerals that make up the earth's crust are light and medium minerals.

Cleavage- this is the ability of minerals to split (split) along parallel, smooth, shiny surfaces called cleavage planes. Cleavage is a property exclusively of crystalline minerals. The cleavage plane corresponds to the crystal face. The following types of cleavage are distinguished:

Very perfect - the mineral easily splits into leaves, plates (mica, talc, lamellar gypsum);

Perfect - when struck with a hammer, fragments are formed, limited by cleavage planes (calcite, halite);

Medium – fragments are limited by both flat and uneven boundaries (orthoclase, augite);

Imperfect – cleavage planes are rarely found (apatite, olivine);

Very imperfect - cleavage planes are practically absent (quartz, pyrite, magnetite).

Kink– cleavage surfaces oriented contrary to cleavage. There are conchoidal (chalcedony, flint, quartz), splinter (selenite, asbestos), granular (rocks), earthy (bauxite, limonite, stepped (orthoclase, galena) and other fracture surfaces.

Color cannot be considered the main diagnostic sign of minerals, because it is changeable and depends on many factors. These are structural features, and the presence of dyes (chromophores), mechanical impurities, cracks and voids. Color is also controlled by environmental parameters such as temperature, humidity, etc. The perception of color by the eyes is also not unambiguous. However, a number of minerals have a permanent color. For example, galena is always gray, cinnabar is red, malachite is green, lapis lazuli is blue, etc. Impurities that cause differences in color and shades very often provide information about the chemical composition. For example, in the group of garnets, magnesium-aluminum pyrope is dark red, calcium-aluminum grossular is light green, calcium-iron andradite is brownish-green, etc. (see: Determinant. “Grenades”, No. 75). When describing the color of a mineral, you should characterize the main color, its depth and shade. For example: dark gray with a bluish tint (for molybdenite). In mineralogy, non-standard color characteristics such as “cochineal red”, “pistachio”, “brass yellow”, “straw yellow”, etc. are often used. However, despite the figurativeness of such definitions, it is better to reduce their use to a minimum.

Trait (strai color)- this is the mark that remains on an unglazed porcelain plate (biscuit) if you draw on it with a mineral. In some cases, it matches the color of the mineral in the piece (cinnabar, magnetite, malachite, etc.). But many minerals are characterized by sharp differences in the color of the line and the piece (pyrite, hematite). A trait is a more permanent diagnostic feature than the color in a piece.

Color and line should be determined in a fresh fracture.

Shine reflects both the internal structure and the nature of the reflective surface of the mineral. Minerals with a metallic luster are easily distinguished. Minerals with a metallic and metallic luster most often have a black or very dark streak (magnetite, galena, graphite); minerals with white and colored streaks usually have a non-metallic luster (gypsum, sulfur, cinnabar). In the group of minerals with a metallic luster, the exceptions are: native gold, copper, silver, platinum, chalcopyrite and faded ores. Having a metallic luster, they give a color line: gold - greenish, silver - silver-white, copper - copper-red, chalcopyrite - greenish, fahlores - dark brown. Non-metallic luster is divided into: polymetallic (the mineral has a metallic luster, but its streaks and powder are colored), diamond, glassy, ​​greasy, silky, pearlescent, matte, etc.