Granite is the largest igneous intrusive rock in the continental crust. This excellent natural material got its name due to its porous-granular structure (from lat. Granum - “grain”).
Granite is classified as acidic rock due to the fact that it contains a large amount of silicon dioxide - SiO2. In addition to this element, the composition of granite includes alkali, as well as magnesium, iron and calcium. This rock is considered one of the most durable, solid and durable, its density is 2600 kg per cubic meter. In our article, we will consider the composition of granite, and also talk about the existing classifications of this rock, and reveal its properties and features.
The origin and occurrence of granite
It is believed that granites were formed over a long period of the geological history of all continents. There are two versions of the origin of the breed in question. The first says that granite is formed as a result of the crystallization of magmatic melt. According to the second theory, the stone under consideration was formed under the influence of ultrametamorphism. Under the influence of pressure, high temperatures and fluids rising from the deep layers of the earth, a granitization process is carried out.
A large number of deposits of this heavy-duty rock are known, including in the USA, China, Brazil, the countries of Scandinavia and Ukraine. In our country, there are also rich deposits of this natural material. It is mined in fifty granite quarries, including in the Arkhangelsk and Voronezh regions, as well as in the Caucasus. Often, various ores are found near the deposits mentioned, including tin, copper, zinc, tungsten, molybdenum and lead.
Consider what is included in granite. Feldspar and Quartz
In terms of its components, this rock is polymineral, that is, consisting not of one component, but of several. One of the main elements that make up granite is feldspar. It is a mineral of the silicate group. As a rule, in granite it is not less than 50%, or even all 60! This
rock-forming mineral is present in the rock in the form of potassium feldspar (orthoclase, adular) and acid plagioclase (oligoclase, bitovnit, labrador, etc.). Another important component of granite is quartz - a very hard rock-forming mineral of the vast majority of igneous rocks. It accounts for no more than 30% of the total volume of the breed in question. Its impregnations look like small glassy grains. In its natural state, quartz is colorless, and as a rock in the composition of granite, it acquires various colors - yellow, pink, red, violet, etc.
Dark-colored minerals and other inclusions in granite
In addition to quartz and feldspar, other inclusions are present in this acidic rock. Usually they occupy no more than 10% of the total. These are biotite, lithium mica, muscovite and hornblende. Accessory - for example, apatite and zircon and alkaline minerals - tourmaline, garnet and topaz, occupy a small proportion. So, we examined the composition of granite. The diagram clearly shows the main components of this natural material.
Types of granite
Depending on the characteristics of the mineral and chemical composition of granite, some of its varieties are distinguished. One of the ranking methods is based on the percentage of plagioclase in the breed. The following types of granite are distinguished:
- alkaline feldspar (less than 10% plagioclase);
- granite proper (from 10% to 65% plagioclase);
- granodiorite (from 65% to 90% plagioclase);
- tonalite (over 90% plagioclase).
In addition to the percentage of feldspar, the basis for distinguishing between the types of the stone under consideration is the content of minor dark-colored minerals. According to this classification, the following rock varieties are distinguished: alaskite - granite, which does not include non-ferrous metals, and leucogranite - having a low content. Two-mica granite - consists, in addition to feldspar and quartz, of muscovite and biotite, and alkaline also contains aegirine and amphiboles.
Structural features of the breed
There is another classification based on the structural and textural features of the mentioned rock. Mostly granite has a granular crystalline structure, but sometimes it is also porphyritic. In the natural environment, the material is located in massive layers that form as a result of cooling of magma. Due to the fact that it solidifies unevenly, granite is formed that has a different structure, including fine and coarse-grained ones. Samples of the latter are called porphyry granite. Granite rapapivi granite (Finland) can serve as an example of a porphyry rock with a coarse-grained structure. It has interspersed orthoclase the size of a chicken egg.
Granite coloring
The minerals that make up granite can stain this rock in various colors. As a rule, it is orthoclase that determines the color of a stone. The most common is light gray. In Russia, red material is quite widespread. The mineral composition of granite with such a bright color includes feldspar, which has hematite crystals, otherwise - iron oxide. They give the rock a blood-red hue. Also come across stones of yellow, blue and pink colors. The breed receives an emerald shade due to the green potassium feldspar - amazonite. Sometimes they find granite of unusual rainbow colors. It appears due to feldspar, which has irisization. Often it is oligoclase and labrador that give a beautiful iridescent flicker, especially noticeable when the stone is turned. This is such an interesting material, granite.
The composition and properties of the rock
This natural material has many wonderful properties that make it indispensable in many areas, especially in the construction industry. Firstly, granite is durable. It can serve for a long time, maintaining its original appearance. Sometimes it is popularly called the "eternal stone", and all because nothing has happened to him for centuries.
Secondly, this material is characterized by extremely high strength. Products from it are not subject to wear. Quartz - a mineral in granite - makes this rock so strong that when it is processed, ground and cut, saws with a special diamond coating are used. Thirdly, one of the most important
properties of granite is its resistance to any environmental influences, as well as to acids. It does not require processing and protection against a variety of oxidative and physical effects. Only at temperatures above 600 degrees can it change its structure and crack. Fourth, granite is resistant to moisture, it is practically waterproof, does not absorb water and is not subject to destruction due to precipitation. For centuries, buildings and monuments made of granite can retain their original appearance. And finally, it is also important that granite is environmentally friendly. It is completely safe for humans. All these properties make the rock under consideration a valuable building material.
Granite application
The mentioned stone is widely used for construction and facing works, as it is characterized by durability, resistance to environmental influences and special strength. Due to its resistance to friction and compression, it is very often used in the external and internal decoration of premises.
Granite has a high resistance to pollution, so it is often used in the manufacture of railings, stairs, columns, countertops, window sills and bar counters. Often with granite slabs fireplaces and fountains are formed, because it is resistant to temperature changes and moisture absorption. In the exterior, this breed is often used as a facing, masonry or building material. Granite paving stones are laid on sidewalks, roads and bridges, often trimmed piers, embankments, streets and squares. Fences, supporting walls are made of granite, they are decorated with facades and walls of buildings. And for this, a breed of the most diverse colors can be used. In Russia, gray, white, red and brown varieties are most often used. Unfortunately, the extraction and processing of igneous rocks is difficult and expensive, therefore this material is rarely used for the construction of ordinary buildings. It is mainly used for decoration of objects of serious architectural value.
Monuments of granite architecture
After proper grinding, the surface of granite becomes as if mirrored, while simultaneously reflecting and absorbing light rays. Therefore, the stone looks very rich and spectacular, which allows you to use it for the manufacture of
monumental sculptures and architectural compositions. Monuments of architecture, historical buildings and structures erected in many countries, including Russia, can serve as an example of the beauty, grace and durability of granite. Any granite structure is particularly majestic and monumental, striking the imagination with its power and beauty.