For many centuries, the main building material was rock. People chose the types of rocks depending on their characteristics, physical properties, strength, density, wear, etc. Since it is not so easy to manually process the stone, in ancient times only the most important objects were erected from it, for example, palaces, defensive constructions, cultural monuments. It is from such natural materials that the legendary Egyptian pyramids, the Great Wall of China, the Aztec pyramid, the Taj Mahal and other famous buildings that are wonders of the world are built.
Characteristic
Different stones are not an accidental accumulation of minerals, but their regular association. The definition of rocks can be formulated as follows: these are aggregates of minerals of natural origin with a constant structure and composition. For the first time this term was used by the Russian chemist and mineralogist V. M. Severgin in 1798. Depending on the strength, decorativeness, density, porosity, frost resistance and other characteristics, minerals find different uses. Rocks are mainly used in construction work.
Rock classification
Depending on the method of their formation, all minerals can be divided into three large groups. Scientists distinguish sedimentary, igneous, and metamorphic rocks; the mantle type belongs to a separate class. These are the natural associations of various substances and minerals that make up a significant part of the earth's crust.
For many centuries, volcanic emissions have been caking and accumulating, magma cools and hardens. Thus, igneous rocks are formed that lie in the upper mantle and in the earth's crust at various depths.
Debris of various origins form a sedimentary type. Thanks to the analysis, specialists determine the type of medium in which the materials were deposited, the features of their origin, the type of agents that carried them, etc.
Metamorphic rocks appear when magmatic and sedimentary species change in the earth’s crust. Such stones have their own unique chemical composition, but they are based on the parent mineral from which they were formed. All metamorphic processes mainly occur in the bowels of the earth's crust.
There are mantle rocks that were originally of magmatic origin, but then underwent significant changes in the mantle.
Igneous rocks
Researchers distinguish two main types of magmatism: effusive and intrusive. They differ in the place of magma solidification, as well as in the nature of its movement. In addition to these two, there are also vein and hypabyssal igneous rocks, which are intermediate types. They give dikes and veins, forming in the cracks of other stones during solidification of magma.
Intrusive or plutonic rocks undergo a long process of formation, which can last more than a millennium. They can contain huge crystals, since magma cools very slowly at great depths. Although plutonic rocks are initially located in the very bowels of the earth's crust, when it is weathered and raised, they very often transform into mountain ranges. A striking example is Mount Spitskoppe in Namibia. The main minerals of this type are granite, labradorite, syenite, gabbro.
The igneous rocks of the effusive (volcanic) type are formed during the eruption of a volcano, that is, when magma comes to the earth's surface. They do not create large crystals due to accelerated cooling. A vivid example of this type of rock is rhyolite and basalt. Of these, in ancient times, various sculptures and monuments were often made.
Sedimentary minerals
Clastic, chemogenic and organogenic are the main sedimentary types of rocks. They vary depending on the mode of origin and are formed on the earth's surface. The debris type is formed due to cementing and caking of individual fragments of various rocks. A striking example of such minerals can serve as sandstones and conglomerates. There is the Montserrat massif in Barcelona, and it is just a conglomerate, since it consists of cobblestones bonded with limestone cement.
Chemogenic types of rocks are formed from mineral particles precipitated in water. It is on the basis of the mineral composition that stones are classified. The most common representative of chemogens is limestone. For example, in Australia there is the Pinnacle Desert, formed just from this breed. The organogenic type is in many ways similar to coal, because it is also formed by caking the remains of animals and plants. All sedimentary rocks are characterized by fracturing, porosity and solubility in water.
Metamorphic minerals
Classes of rocks are often quite arbitrary. Minerals of both sedimentary and magmatic origin can belong to the metamorphic type. They have varying degrees of intensity of transformation processes. If it is low, then metamorphism allows you to determine the mother breed, but with a high degree to do this is simply impossible. Such minerals change their composition and texture. For this reason, metamorphic rocks are divided into shale and non-shale, and depending on the conditions of formation, there are three large groups: regional, hydrothermal and contact metamorphism.
Sometimes it happens that huge boulders of stones are exposed from outside, for example, low or high temperatures, pressure. A vivid example is gneiss. These minerals can be considered regional. Hydrothermal metamorphism occurs with the participation of thermal springs. Minerals come in contact with an ion-rich hot fluid, wading through mountain cracks, and a chemical reaction occurs that changes the composition of the rocks. An example is quartzite, often formed by limestone. There is also contact metamorphism. In this case, rocks are chemically affected by an increase in temperature by intrusive igneous masses.
Rock properties
There are several properties of minerals, and all of them are important to one degree or another. If they are used as a facing material, then first of all, attention is paid to their aesthetic appeal. In some cases, the decorativeness of a stone is very important, its pattern and color are selected. The density of the rock determines how much the rock weighs. Types of rocks are light and heavy. The former have a density indicator of up to 2200 kg / m 3 , while the latter have more than 2200 kg / m 3 . If a stone is chosen for the construction of a structure, then its weight must be taken into account, the denser it is, the heavier the structure will be. This parameter depends on the composition of the rock, porosity.
One of the most important properties of stone (especially when it comes to construction) is strength. The wear resistance of the material depends on it. The stronger the mineral, the longer it will retain its original appearance. In this regard, all stones are divided into three groups: low, medium strength and durable. It all depends on the composition of the rock, namely the hardness of the minerals. Gabbro, granite, quartzite can be attributed to strong stones, limestone, marble, travertine to the middle ones, tuffs, loose limestones have low strength.
Different types of rocks have varying degrees of porosity. Acid and salt resistance, water absorption of stone depends on this characteristic. Particular attention should be paid to porosity if a particular breed is selected as a cladding. This indicator determines the durability of the material, its polishability, strength, decorativeness, heat conductivity, workability, etc. The higher the porosity, the lower the weight of the stone, it is better processed, but at the same time its volume, strength, and polishability decrease.
The rate of water absorption of the rock is also very important. The frost, acid and salt resistance of the material depend on it. Water that gets into the pores, when frozen, increases in volume, creates pressure, due to which cracks eventually form. The same thing happens with saline solutions, which contribute to the growth of crystals, creating additional pressure. If the porosity of the mineral is low, then cracks appear in it, in some cases it may even crack. In porous stones, the pressure is evenly distributed, and no cracks appear.
The process of changing rocks is largely affected by their acid resistance. Acids can convert and even destroy some minerals. Therefore, when choosing a stone for the construction of structures, this fact must be taken into account. For example, hydrochloric acid is a serious threat to marble, dolomite, travertine. But limestone and granite are characterized by excellent acid resistance, so so many iconic structures made of these materials have survived to this day.
Conversion processes
Huge boulders, majestic mountain ranges give the impression of mighty giants over which time and various external factors are not dominant. They seem to retain their original appearance for centuries and millennia, but this is not at all. Over time, any rocks undergo significant changes. Classification of rocks allows you to determine how long the minerals retain their original appearance, which exactly has the greatest impact on them.
The composition of the stone changes over a long period. Rock transformation can be natural or man-made. Factors such as meltwater or groundwater, rain, wind, sun, high and low temperatures influence the condition of stones. The destruction of rocks in a natural way is very slow, but it cannot be stopped. Rain and wind wash and weather both the upper layers and underground landscapes. Gradually, they change not only the form, but also the composition of the minerals.
Anthropogenic processes are associated with human activities. Rock destruction can be carried out using technology. For example, construction crews repeatedly cleared the territory for the construction of structures, while removing part of the mountain ranges. Of course, such activity destroys the natural landscape, has a negative impact on it. Damaged rocks give cracks, because of this, collapse, landslides occur. A person can change the appearance of mineral deposits much faster than natural factors.
Thus, absolutely all mountainous terrain change their appearance over time. The speed of their transformation largely depends on external conditions, rock composition, strength, degree and duration of exposure. The transformation process is also affected by the climate of the area in which the stones are located.
Rock cycle
The geological processes of the formation of magmatic, sedimentary, and metamorphic minerals are tied into a certain cycle. It all starts with the fact that magma spills out, gradually cools and solidifies, while magmatic rocks are formed. The types of rocks change as soon as they appear on the earth's surface. Wind, water, temperature changes form a sedimentary type of minerals. The stones are crushed, weathered, transferred from place to place, stopping in sedimentary basins. It is there that rock fragments complete their path, coalesce and turn into a sedimentary type of minerals. Over time, mountain ranges plunge to great depths, being exposed to tectonic processes. All this leads to the formation of metamorphic rocks. At high temperature and strong pressure, the minerals melt, turning into magma. Over time, it solidifies, forming an igneous rock, and the process of stone formation begins again.
Petrology and Petrography
At both the micro and macro levels, minerals are being studied. In the first case, only small particles of certain rocks, their transparent and translucent saw cuts, are studied. This allows you to set the characteristics and properties of minerals. In the second case, scientists consider all rocks in aggregate, because they form a certain element of the earth's crust. Researchers manage to determine the history, features and the approximate date of their formation.
The origin of rocks is studied by two disciplines: petrology and petrography. The first science examines the chemical and mineralogical composition of stones, the conditions of their occurrence, texture and structure. Petrology also determines the geological formations that make up the bulk of the earth's crust. Petrography is engaged in the classification and description of various breeds; it is more a descriptive science. She studies individual samples of stones, their structure and composition. Petrographs work with transparent and translucent sections, using a microscope they examine the properties of their components. Scientists can also work with rock samples of impressive size.
There are several levels of mineral research. First, scientists are engaged in compiling geological maps, then field, petrographic and geochemical surveys are carried out. All of them complement each other and allow you to complete the picture. Field studies make it possible to determine structural features, the position of minerals, and establish an approximate time frame for their occurrence. Petrographic works determine what rocks exist by origin, what is the percentage of minerals in them.
A more complex science is petrology. The need for special and deeper research arose as a result of the accumulation of a huge baggage of knowledge. Rocks include different types of minerals that correspond to sedimentary, igneous, and metamorphic types. And each of them is the subject of study of a certain branch of the mentioned discipline. So, the science of sedimentary minerals is interested in the texture and composition of salts, limestones, sandstones, conglomerates and other stones of sedimentary origin. Magmatic petrology considers minerals crystallized from molten magma. Metamorphic science studies marble, slates, gneisses and other rocks formed during the transformation.
Among other things, scientists are also engaged in geochemical research. They give a general idea of the chemical composition of the rock, its age, place of origin, mineral phases, temperature and pressure at which it was formed.
The most common rocks
On our planet there is a huge number of deposits of various minerals. Most of them have found practical application. Some breeds are more in demand, some less. Let's talk about the stones most often used by man.
Granites
Perhaps this is the most common stone, consisting of quartz, feldspars, mica. Granite has a granular crystalline structure, is divided into three categories: fine, medium and coarse-grained. The stone has a variety of shades, the rarest are bluish-green, light gray and burgundy. Granite is very polishable, some of its varieties are subjected to heat treatment. This is done to create additional decorative effects. The performance and mechanical properties of granite are rated very highly, so the stone is used for cladding facades of structures, embankments, and in the construction of basement structures. Stone is also used to create sculptures.
Sandstones
Another popular rock formation. The types of rocks depend on the method of formation. Sandstones are sedimentary because they consist of cemented sand. There are stones of various colors in nature: green, yellow, gray, red, brown. For decorative purposes, fine-grained brown, red and green sandstones are most often used. Basically they go to the cladding of buildings.
Marble
Belongs to a granular-crystalline rock, appeared as a result of exposure to dolomite and limestone of high temperature and pressure. Marble has high decorative properties, it lends itself well to processing. , , , , , . , .
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