For the most part, a rock-forming mineral is one of the main components of the earth's crust - a rock. The most common are quartz, micas, feldspars, amphiboles, olivine, pyroxenes, and others. Meteorites and lunar rocks are also referred to them. Any rock-forming mineral belongs to one or another class - to the main, which are more than ten percent, minor - up to ten percent, accessory - less than one percent. The main, that is, basic, are silicates, carbonates, oxides, chlorides or sulfates.
Differences
Rock-forming mineral can be light (leucocratic, salic), such as quartz, feldspathoids, feldspars, and the like, and dark (melanocratic, mafic), like olivine, pyroxenes, amphiboles, biotite, and others. They are also distinguished by composition. The rock-forming mineral is silicate, carbonate or halogen rocks. Paragenesis - a combination of different types that determine the name, is called cardinal. For example, oligoclase is combined with granites,microcline or quartz.
Groups of rock-forming minerals that give a place to a rock in petrographic taxonomy - diagnostic or symptomatic. These are quartz, feldspathoids and olivine. Minerals are also distinguished as primary, syngenetic, forming the entire rock, 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.
Properties of minerals
Crystal structure and chemical composition determine all the properties of minerals. Diagnostics is carried out 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 isolation. 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 specific minerals.
Monomineral and polymineral rocks
Rocks of stones are accumulations of natural mineral masses covering the surface of the Earth, taking part in the construction of its crust. Here, as already mentioned, substances completely different in chemical composition are involved. Those rocks whose composition is one single mineral are called monomineral, and all others, consisting of two or more types of rocks, are called polymineral. For example, limestone is entirely calcite, so it is monomineral. But granites are diverse. They include quartz, and mica, and 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 very area 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 many stones, they all seem 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 occurred, sedimentary, metamorphic and igneous rocks are distinguished. Igneous rocks are those formed from the eruption of magma. The red-hot, molten stone, cooling down, turned into a solid crystalline mass. This process continues today.
Molten magma has a huge amount of chemical compounds that are affected by high pressure and temperature,while many compounds are in the gaseous state. The pressure pushes the magma to the surface or comes close to it and begins to cool. The more heat is lost, the sooner the mass crystallizes. The rate of crystallization also determines the size of the crystals. On the surface, the cooling process is fast, gases escape, so the stone turns out to be fine-grained, and large crystals form in the depths.
Erupted and deep crystalline rocks
Crystallized magma is divided into two main features that give the groups their names. The igneous rocks include a group of effusive, that is, erupted, as well as a group of intrusive - deep crystallization. As already mentioned, magma cools under different conditions, and therefore the rock-forming mineral turns out to be different. The outpouring with the volatilization 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, and therefore the crystals are large in structure.
The outflowing rocks are represented by bas alts 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, there are twenty times more of them than all the others. Primary igneous rocks, depending on the composition of quartz, are divided into five groups. Crystalline rocks include a lot of impurities, among which it is necessary to note a variety of micro- andultramicroelements, 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 of steam. When magma moves up to the surface, the amount of the latter is greatly reduced. When cooled, magma forms silicate, a mineral that is a variety of silica compounds. All minerals of this kind are called silicates - with s alts of silicic acids. Aluminosilicates contain s alts of aluminosilicic acids.
Bas altic magma is basic, it has the widest distribution and consists of half silica, the remaining fifty percent is magnesium, iron, calcium, aluminum (significantly), phosphorus, titanium, potassium, sodium (less). Bas alt magmas are subdivided into tholeiite supersaturated with silica and olivine-bas alt enriched in alkalis. Granite magma is acidic, rhyolite, it contains even more silica, up to sixty percent, but in terms of density it is more viscous, less mobile and highly 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 -rock-forming and igneous, and metamorphic origin. Silicates are also found in sedimentary rocks, and some of them serve as jewelry for humans, ore for obtaining 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 an ionic tetravalent group SiO4 - a double tetraerd. Silicates are island, ring, chain, tape, sheet (layer), frame. This division depends on the combination of silicon-oxygen tetraerds.
Breed classification
Modern taxonomy in this area began in the nineteenth century, and in the twentieth century it developed tremendously as the science of petrography-petrology. In 1962, the Petrographic Committee was first created in the USSR. Now this institution is located in Moscow IGEM RAS.
By the degree of secondary changes, effusive rocks differ as cainotype - young, unchanged, and paleotype - ancient, which recrystallized over time. These are volcanogenic, clastic rocks, which were formed during the eruption and consist of pyroclastites (debris). Chemical classification implies division into groups depending on the content of silica. Igneous rocks can be ultrabasic, basic, intermediate, acid and ultra-acid in composition.
Batholiths and stocks
Very large, irregular massifs of intrusive rocks are called batholiths. The area of suchformations can be calculated in many thousands of square kilometers. These are the central parts of the folded mountains, where the batholiths extend over the entire mountain system. Composed of coarse-grained granites with outgrowths, processes and protrusions, formed from the intrusion of granitic magma.
The stem has an elliptical or rounded shape in cross section. They are smaller than batholiths in size - often a little less than a hundred square kilometers, sometimes - all two hundred, but they are similar in other properties. Many stocks protrude from the mass of the batholith like a dome. Their walls are steeply falling, the outlines are wrong.
Laccoliths, etmolites, lopolites, dikes
Mushroom-shaped or dome-shaped formations formed by viscous magmas are called laccoliths. They are more common in groups. They are small in size - up to several kilometers in diameter. Laccoliths, growing under the pressure of magma, lift the rock without disturbing the layering of the earth's crust. They are very similar to mushrooms. Etmolites, on the contrary, are funnel-shaped, with a thin part down. Apparently, a narrow hole served as an outlet for magma.
Lopolites have saucer-shaped bodies, convex downwards and with raised edges. They also seem to grow out of the ground, not disturbing the earth's surface, but as if stretching it. Cracks appear in the rocks sooner or later - for various reasons. Magma feels weak spots 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. This is how dikes are formed. They are small - in diameter from half a meter to hundreds of meters, but evendo not exceed six kilometers. Since the magma in the fissures cools rapidly, the dikes are always fine-grained. If narrow ridges are visible in the mountains, the rocks are most likely dikes because they are more resistant to erosion than the surrounding rocks.
