For the most part, the rock-forming mineral is one of the main components of the earth's crust - rock. The most common are quartz, mica, feldspar, amphiboles, olivine, pyroxenes and others. Meteorites and lunar rocks are also attributed to them. Any rock-forming mineral belongs to one or another class — the main ones, of which more than ten percent, minor ones — up to ten percent, accessory — less than one percent. The main ones, i.e. the main ones, are silicates, carbonates, oxides, chlorides or sulfates.
Differences
The rock-forming mineral can be light (leucocratic, salic), such as quartz, feldspathoids, feldspars, and the like, and dark in color (melanocratic, mafic), like olivine, pyroxenes, amphiboles, biotite, and others. They are also distinguished by composition. The rock-forming mineral is silicate, carbonate or halogen rock. Paragenesis - a combination of various types that determine the name, called cardinal. For example, oligoclase, microcline, or quartz are combined with granites.
The groups of rock-forming minerals that give the rock a place in petrographic taxonomy are diagnostic or symptomatic. These are quartz, feldspathoids and olivine. Minerals are also distinguished primary, syngenetic, forming the entire breed, and secondary, arising during the transformation of the rock. The chemical elements that make up the main rock-forming minerals are called petrogenic. These are O, H, F, S, C, Cl, Mg, Fe, Na, Ca, Si, Al, K.
Mineral Properties
The crystal structure and chemical composition determine all the properties of minerals. Diagnostics is performed using a variety of analytical methods - spectral analysis, chemical, electron microscopic, X-ray diffraction. In field practice, the simplest (diagnostic) properties of minerals are determined purely visually, by eye. Most of them are physical. However, the exact determination of the mineral requires a whole range of diagnostic methods. Some properties of different minerals may coincide, while others may not.
It depends on the presence of mechanical impurities, chemical composition and forms of excretion. Quite rarely, the basic properties are so characteristic that they can accurately diagnose any mountain stone. Diagnostic properties are divided into three groups. Optical and mechanical groups due to their properties allow the determination of properties for all stones without exception. The third group - others, with properties used to diagnose highly defined minerals.
Monomineral and polymineral rocks
Rock rocks are clusters of natural mineral masses that cover the Earth's surface, taking part in the construction of its crust. Here, as has already been said, completely different substances are involved in the chemical composition. Those rocks whose composition is one single mineral are called monomineral, and all others, consisting of two types of rocks and more - polymineral. For example, limestone is entirely calcite; therefore, it is monomineral. But granites are diverse. They include quartz, mica, feldspar, and much more.
Mono- and polyminerality depends on what geological processes have occurred in the area. You can take any mountain stone and determine the exact region, even the area itself, where it was taken. They are similar to each other, and at the same time almost never repeat. These are all the studied rocks. There are a lot of stones, everything seems to be the same, but their chemical properties were formed as a result of different processes.
Origin
According to the conditions in which the formation of mountains, sedimentary, metamorphic and igneous rocks are distinguished. To igneous rocks is one that was formed from an eruption of magma. The hot, molten stone, cooling, turned into a solid crystalline mass. This process continues today.
In molten magma there is a huge amount of chemical compounds that are affected by high pressure and temperature, despite the fact that many compounds are in a gaseous state. Pressure pushes magma to the surface or comes close to it and starts to cool. The more heat is lost, the sooner the mass crystallizes. The crystallization rate also determines the size of the crystals. On the surface, the cooling process is quick, the gases evaporate, so the stone turns out to be fine-grained, and large crystals form in the depths.
Spilled and deep crystalline rocks
Crystallized magma is divided according to two main features that give the groups names. The igneous rocks include a group of effusive, that is, poured, as well as a group of intrusive - deep crystallization. As already mentioned, magma cools under different conditions, and therefore the rock-forming mineral is different. Outflowing with the escape of gases is enriched in some chemical compounds and becomes poorer in others. The crystals are small. In deep magma, chemical compounds do not find new ones, heat is lost slowly, therefore, crystals are large in structure.
The erupted rocks are represented by basalts and andesites, almost half of them, liparite is less common, all other rocks in the earth's crust are insignificant. In the depths, porphyries and granites are most often formed; they are twenty times more than all the others. Primary igneous rocks are divided into five groups depending on the composition of quartz. Crystalline rocks include a lot of impurities, among which it is necessary to note a variety of micro- and ultramicroelements, thanks to which all kinds of plants cover the earth's crust.
Magma
Magma contains almost the entire periodic table, dominated by Ti, Na, Mg, K, Fe, Ca, Si, Al, and various volatile components - chlorine, fluorine, hydrogen, hydrogen sulfide, carbon and its oxides, and so on, plus water in the form couple. When magma moves up to the surface, the number of the latter is significantly reduced. When cooling, magma forms a silicate - a mineral, which is a variety of silica compounds. Minerals are called silicates of all such planes - with salts of silicic acids. Aluminosilicates contain salts of aluminosilicic acids.
Basaltic magma is basic, it has the widest distribution and is half composed of silica, the remaining fifty percent is magnesium, iron, calcium, aluminum (significantly), phosphorus, titanium, potassium, sodium (less). Basaltic magmas are subdivided into oversaturated silica - tholeiitic and alkali-enriched olivine-basaltic. Granite magma is acidic, rhyolitic, with even more silica in it, up to sixty percent, but in density it is more viscous, less mobile and very saturated with gases. Any volume of magma is constantly evolving, under the influence of chemical processes.
Silicates
This is the most widespread class of natural minerals - more than seventy-five percent of the total mass of the Earth's crust, as well as a third of all known minerals. Most of them are rock-forming and of magmatic and metamorphic origin. Silicates are also found in sedimentary rocks, and some of them serve man as jewelry, ore to produce metals (iron silicate, for example) and are mined as minerals.
They have a complex structure and chemical composition. The structural lattice is characterized by the presence of the tetravalent ionic group SiO 4 - a double tetraerd. Silicates are island, ring, chain, ribbon, sheet (layered), frame. This separation depends on the combination of silica-oxygen tetraerds.
Breed classification
Modern taxonomy in this area began in the nineteenth century, and in the twentieth was greatly developed as the science of petrography-petrology. In 1962, the Petrographic Committee was first established in the USSR. Now this institution is located in Moscow IGEM RAS.
By the degree of secondary changes, effusive rocks differ as kainotype - young, unchanged, and paleotypic - ancient, which recrystallized over time. These are also volcanic, detrital rocks that formed during the eruption and consist of pyroclastites (debris). Chemical classification implies the division into groups depending on the silica content. Igneous rocks in composition can be ultrabasic, basic, medium, acidic and ultra-acidic.
Butoliths and stocks
Very large, irregularly shaped massifs of intrusive rocks are called batholiths. The area of such formations can be estimated in many thousands of square kilometers. These are the central parts of the folded mountains, where the batholiths extend over the entire mountain system. They are composed of coarse-grained granites with growths, processes and protrusions, formed from the introduction of granite magma.
The stem is elliptical or rounded in cross section. They are smaller than batholiths in size - often a little less than one hundred square kilometers, sometimes - all two hundred, but are similar in other properties. Many stocks protrude from the mass of batholith like a dome. Their walls are steeply falling, the shape is wrong.
Laccoliths, ethmolites, lopolites, dikes
Mushroom or domed formations formed by viscous magmas are called laccoliths. Meet more often in groups. They are small in size - up to several kilometers in diameter. The laccoliths, growing under the pressure of magma, are raised without disturbing the stratification of the earth's crust. What are very similar to mushrooms. The ethmolites, in contrast, are funnel-shaped, with a thin part down. Apparently, a narrow hole served as an exit to magma.
Lapolites have saucer-shaped bodies, convex downward and with raised edges. They also seem to grow out of the earth, not violating the earth's surface, but as if stretching it. Cracks appear in the rocks sooner or later - for various reasons. Magma feels weaknesses and under pressure begins to fill all the gaps and cracks, at the same time absorbing the surrounding rocks under the influence of huge temperatures. So dikes are formed. They are small - in diameter from half a meter to hundreds of meters, but even six kilometers do not exceed. Since magma cools quickly in cracks, dikes are always fine-grained. If narrow ridges — rocks, are visible in the mountains — these are most likely dikes, because they are more resistant to erosion than the surrounding rocks.