Granite is the most numerous igneous intrusive rock in the continental crust. This excellent natural material got its name due to its porous-granular structure (from Latin granum - "grain").
Granite is classified as an acid 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 strongest, hardest and most durable, its density is 2600 kg per cubic meter. In our article, we will consider the composition of granite, as well as talk about the existing classifications of this rock, reveal its properties and features.
Origin and occurrence of granite
Granites are believed to have formed over a long periodgeological 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 process of crystallization of magmatic melt. According to the second theory, the stone we are considering was formed under the influence of ultrametamorphism. Under the influence of pressure, high temperatures and fluids rising from the deep layers of the earth, the process of granitization is carried out.
A large number of deposits of this heavy-duty rock are known, including in the USA, China, Brazil, Scandinavian countries and Ukraine. There are also rich deposits of this natural material in our country. 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 mentioned deposits, including tin, copper, zinc, tungsten, molybdenum and lead.
Consider what is included in granite. Feldspar and quartz
In terms of its components, this rock belongs to polymineral, that is, it consists 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 at least 50%, or even all 60! This rock-forming mineral is present in the rock in the form of potassium feldspar (orthoclase, adularia) and acid plagioclase (oligoclase, bytonite, labradorite, etc.). Another importanta component of granite is quartz - a very hard rock-forming mineral of the vast majority of igneous rocks. No more than 30% of the total volume of the rock under consideration remains on its share. Its inclusions look like small glassy grains. In its natural state, quartz is colorless, but as a rock in the composition of granite, it acquires a different color - yellow, pink, red, purple, etc.
Dark colored minerals and other inclusions in granite
In addition to quartz and feldspar, there are other inclusions in this acidic rock. Usually they occupy no more than 10% of the total volume. These are biotite, lithium micas, muscovite and hornblende. An insignificant share is occupied by accessory minerals - for example, apatite and zircon and alkaline minerals - tourmaline, garnet and topaz. 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 rock. There are the following types of granite:
- alkaline feldspar (less than 10% plagioclase);
- granite itself (from 10% to 65% plagioclase);
- granodiorite (from 65% to 90% plagioclase);
- tonalite (over 90% plagioclase).
In addition to the percentage of feldspar, the content of minordark colored minerals. According to this classification, the following types of rock are distinguished: alaskite - granite, which does not include dark-ferrous metals, and leucogranite - having a low content of them. 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 formed as a result of magma cooling. Due to the fact that it hardens unevenly, granite is formed, which has a different structure, including fine and coarse-grained. Samples of the latter are called granite-porphyries. Granite-rapakivi (Finland) can serve as an example of a porphyritic rock with a coarse-grained structure. It has flecks of orthoclase the size of a chicken egg.
Granite coloring
The minerals that make up granite can color this rock in different colors. As a rule, it is orthoclase that determines the color of the stone. The most common is a light gray color. In Russia, red material is quite widespread. The mineral composition of granite with such a bright color includes feldspar, which has crystals of hematite, otherwise iron oxide. It is they who give the rock a blood-red hue. Also come acrossyellow, blue and pink stones. The emerald shade of the rock is due to the green potassium feldspar - amazonite. Sometimes they find granite of an unusual iridescent color. It appears due to feldspar, which has iridescence. Often it is oligoclase and labrador that give a beautiful iridescent shimmer, especially noticeable when turning the stone. This is such an interesting material, granite.
Composition and properties of rock
This natural material has many remarkable properties that make it indispensable in many areas, especially in the construction industry. First, granite is durable. It can serve for a long time, retaining its original appearance. Sometimes people call it the "eternal stone", and all because absolutely nothing happens to it for centuries.
Secondly, this material is extremely durable. Products from it are not subject to wear. Quartz, a mineral in granite, makes this rock so strong that saws with a special diamond coating are used in its processing, grinding and cutting. 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 from a variety of oxidative and physical influences. 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 does notsubject 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 considered rock the most valuable building material.
Use of granite
The mentioned stone is widely used for construction and facing works, as it is durable, resistant to environmental influences and especially durable. Due to its resistance to friction and compression, it is very often used in interior and exterior decoration.
Granite has a high resistance to dirt, so it is often used in the manufacture of railings, stairs, columns, countertops, window sills and bar counters. Often fireplaces and fountains are decorated with granite slabs, because it is resistant to both temperature extremes and moisture absorption. In the exterior, this breed is often used as a facing, masonry or building material. Sidewalks, roads and bridges are laid out with granite paving stones, piers, embankment streets and squares are often trimmed. Fences, supporting walls are made of granite, facades and walls of buildings are decorated with it. And for this, a breed of a wide variety of 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, so this material is rarely used for the construction of ordinary buildings. It is mainly used fordecoration of objects of great architectural value.
Granite architectural monuments
After proper polishing, the surface of granite becomes like a mirror, simultaneously reflecting and absorbing light rays. Therefore, the stone looks very rich and spectacular, which allows it to be used for the manufacture of monumental sculptures and architectural compositions. An example of the beauty, grace and durability of granite can be architectural monuments, historical buildings and structures erected in many countries, including Russia. Any granite structure is distinguished by its special majesty and monumentality, striking the imagination with its power and beauty.
