It’s interesting to know! The geological information about granite.

Originally rocks (mountain breeds) are divided into igneous or magmatic. Granite and basalt are magmatic; sandstone and limestone are sedimentary breeds; metamorphic, for example, are gneisses, crystal slates, marble and graphite.  

Granite   is the most widespread in continent earth crust sour  holocrystalline magmatic rock (mountain breed), which consists mainly of quartz, potassium feldspar (ortoklaz, nitraklin), sour plagioklaz and mica (biotite, muskovit). Closeness of granite is 2600 kg/m³, compression durability makes up to 300 MPa. Granite is perfect building material.

Granite and its building properties

Granite is poly-mineral sour rock (mountain breed), one of the most widespread magmatic breed on the Earth.  We don’t mean taste qualities when we call granite “sour” breed.   The question is about high maintenance of silica.

Granite components:

-          potassium feldspar (orthoclase) – 40-70%,

-          quartz, being the most proof component part of granite – 20-40%,

-          micas (muskovit or biotite) – 5-20%.

Potassium feldspar and micas are little-proof constituents. Granite firmness depends on them. If weathering of feldspars begins, the further destruction of a stone goes rather quickly. If instead of mica other minerals enter the complement of granite, for example, augite, the word “augitic” is added accordingly to the name of granite breed.

Granite can be of different colors. Most kinds granite are grey. However granite can be black, dark-red and rarer green or bluish-grey color? What does it depend on? It depends on mineral composition (components) of granite. The color of feldspar especially strongly influences the decorativeness of granite. But feldspars are white. Feldspar breeds get grey and black colors from the admixture of dark-colored minerals - mica or pyroxenes.

So, granite consists of three main minerals: quartz and two kinds of feldspars (potassium and calcium-sodium) and mica. They form the structure of granite with equal amounts (30%). They all are colourless or white. And pyroxenes, amphibole or mica, being dark minerals, make 10%; they will be noticed in granite as separate scales or grains. Let's look at a stone from a distance. Everything merges into grey colour. Obviously, the more dark minerals has granite - the darker it is. The color of some granite seems darker because of quartz which can be presented by morion.

How does granite become red? Bright red or pink feldspar are included into their mineral composition. They can be met in all parts of the world. The smallest crystals of hematite (oxid of iron) and red iron ore, disseminated regularly on all crystal of feldspar, give coloring to feldspar. Painting abilities of hematite are exclusively great. Feldspar takes thick red coloring already when there is 0,7-1,0% of hematite in it. Granite feldspar acquires the pink coloring when maintenance of hematite does not exceed 0,3-0,4%. So, red color of granite is a result of difficult and not always ordinary processes.

Well, and how does granite become green? Such color is given to granite due to inclusions of green potassium feldspar which is known for a long time as a semiprecious stone - amazon-stone (=amazonite). It was used by American Indians many years ago before Columbus had discovered America, by inhabitants of old Egypt and Ethiopia as decorations. The amazon-stone (amazonite) was found in the Ilmensky mountains in 1784. It was also found in Kolsky peninsula during Soviet times. The Nature of amazon-stone (amazonite) coloring is not clear up to this moment. There is a hypothesis, that at the beginning usual red and white feldspar was crystallized, which subsequently under the influence of the flying substances, accumulating in the central part of a vein, turned into amazone-stone (amazonite). Anyhow, the green granite exists and is very beautiful. The variety of green granite is blue granite. And, finally, there is granite, in which structure there is a feldspar, possessing iridization (iridize), in other words - bright reflexion. While polishing unusual coloring which can be compared to a coloring of the peacock tail is found out.

Granite is not only nice stone, but it is also very strong stone. As me mentioned above, granite has a big durability at compression. Its durability while stretching consists only of 1/60 to 1/40 strength at compression. According to their grains, people differ fine-grained, medium-grained and coarse-grained kinds of granite. Fine-grained granites are better resistible to mechanical influences. They are more proof at deterioration, more steady against aeration and burst at heating, than medium- and coarse-grained granite. The coarse-grained granites are insufficiently fire-resistant. They increase in volume and burst at heating. That’s why, stairs and tiles after fire often burst in big buildings and houses.

Granites are well processed. We can split, saw, flame, polish and square granite. Thanks to remarkable properties of granite, such as high durability at compression (from 120 to 300 МPа), rather small durability at stretching, big density, small water absorption (less than 0,5-0,8 % on volume), high frost resistance, very considerable heat conductivity, steady against deterioration, that’s why it is widely applied as a building and facing material. Monumental constructions rested upon the bases from granite; it is used in building bridges, quays and socles of large buildings; rabble from a granite lays in the basis of motorways; the stone blocks from granite pave out streets of many cities.

Don’t forget about  big monoliths.  The world's largest is the Aleksandrovska column, erected on the Palace area in Leningrad (Saint-Petersburg). Its weight is 3700 tones, height is 25,6 m, together with a pedestal and a bronze figure of 47,5 m. It is made from the Vyborg coarse-grained granite rapakiwi. Monolithic columns of the Isaakievsky Cathedral 17 m. height are created from the same granite.

Recollect the Egyptian sphinxes on a quay of the Neva in Leningrad (Saint-Petersburg). They are made from  monoliths of red granite polished to mirror shine. And the Copper horseman, a monument to Peter I? Its pedestal is cut from a large granite boulder (13,2x6,6x8,1) which is named by people a thunder-stone as it has been split by a strong lightning stroke. It is amazingly beautiful, huge granite monolith. At last, the monument to Charles Marx is cut from a monolith of a granite in the size 15x5x3,6 m,  its weight 750 tones, it is established in Moscow on Sverdlova area (the Kudashevske deposit in the Dnepropetrovsk region). It is possible to tell about granite, that it was a noteworthy breed in ancient times and remained such till these days.  Granite deposits are available in Karelian Republic, on Kola peninsula, in Urals Mountains, in Siberia, Central Asia, in the southwestern part of Ukraine and in the North Caucasus.

Close to the granite rocks (breeds) are syenites (sienites) and diorites. They look like granites and possess the same crystalline grainy structure.

 

Characteristic (Description) of granite

 

Structure of granite:

 

“Q” is quartz; “O” is orthoclase; “M” – is mica

 

Granites (from Latin “granum” means grain) are the most widespread deep rocks (breeds) with the brightly expressed grainy and crystalline structure. Firstly term “granite” was applied in literature by Italian mineralogist Andrea Cezalpino in 1596. They consist of feldspars (usually 40...60%), quartz (20...40%), mica, silicates - augite, amphiboles, rarer pyroxenes (not more then 10%). People distinguish three structures of granites in according to their grains:

 

- fine-grained (to 2 mm),

 

- middle-grained (from 2 to 5 mm),

 

- coarse-grained (over 5 mm).

 

Color of granites depending on the kind and coloring of feldspars are more frequent grey (from light - to dark grey) with different tints, pink, orange, red, blue-grey, sometimes blue-green.

Granite coloring is influenced by dark-coloring elements (biotite, augite and other) which usually give a stone a darker color and quite often greenish tint (Yancevskiy granite). The quartz in structure of granites is colorless and that is why doesn’t influence the character of their coloring. There are granites with black quartz in the wild nature (people call them black-quartz granite) or purple-pink (amethystine granites of Sweden). Granites are exceptionally rare with blue quartz (for example, Serebryanske deposit in the Murmansk area). Fine-grained light-grey granite with a blue tint, red with deep dark tone and green-grey varieties of granites are most valuable in a decorative relation.

The surface draw of granites is enough monotonous and conditioned by the accumulation of dark-color minerals or feldspars and quartz. Coarse-grained granites have usually the same type spotted (speckled) picture. The general background of red coarse-grained granites is created due to the large densely located crystals of microlite, determining the color of breed. Looking at it very closely sometimes you can see a picture of ring-type chainlet of dark quartz and black biotite on the background, surrounding the crystals of microlite (Omelyanovsky granite). In cases, the inlaid picture of granites is enriched with sparkling crystals of feldspar due to the brilliant planes of joints in the fractures of disseminations (Korninsky granite). Color and picture of some red granites with the giant crystals of feldspars measuring to 80...120 mm is usually conditioned by the accumulations of grains of this mineral (Kapustinsky granite). In the cases when such crystals have a flat form and are extended on long axes in one direction, the process of sawing of rock (breed) in a transversal plane allows to expose an exceptionally original dotted-striped picture.

The accumulations of dark-color minerals and feldspars can comparatively rare form wavy-striped or smoke-colored (cloudy) picture, giving granite the special decorativeness (Shalsky, Syuskiyansaarsky types of granite and some other types of granite). Sometimes the presence of  quartz veins in them can influence the character of fine- and middle-grained granites picture and, as a rule, deteriorative the decorativeness of rock (breed) (Yancevsky granite and other). The usual granite  middle closeness is 2600... 2800 kg/m3, weak porosity (to 1,5%), insignificant water absorption (0,5%), steady against deterioration; strength at a compression - 90...280 MPa and higher. Everlasting of granite (especially its fine-grained varieties) is high. In cases, its service term in constructions reaches 1000 years and more.

Granite is usually polished well, saving a mirror surface in outward revetment (facing) for a long term, easily added to grind, acquiring different chopped finishes. The relief finishes of granite especially successfully underline monumentalism of constructions; the interesting decorative game effect of light treatment and shade on a stone surface is thus reached, combining sometimes with the spangles of mica plates. Some varieties of granites get a high decorative finish after flame process (it belongs, foremost, to the light-grey rocks (breeds), acquiring tender almost sugar-white type of tint).

Due to high mechanical indexes and operating properties, granites are widely used in building as facing tiles, in architecture, details of revetment (facing) of hydro-technical buildings, foundations of bridges, kerbstones (border stones) paving, etc. The fine-grained homogeneous varieties of granite of light-grey and pink colors apply as sculptural material taking to account that their fine-grained structure assumes striking process without formation of not directed splits. Granites with a coarse-grained structure are successfully used for erection of large monumental buildings and implementation of revetments (facings) of pedestals to the monuments. \" There is not a single stone which is perfectly combined with bronze, as granite\", - the well-known Russian sculptor B.I . Orlovskiy said.

Main districts of granite distribution in our country are situated in Ukraine, in Karelia, in Middle Asia and in Ural.

One of structural varieties of granite is a pegmatic granite - pegmatite (from Greek “pegma” means “cleating”, “fastening”) – this is rock (breed) at which quartz and feldspar appropriately germinate in each other. Characteristic representative of this variety - writing granite, in which feldspar germinates in it by thin wedge-shaped formations of quartz, reminding ancient Jewish inscriptions. Due to high decorative qualities and original picture, writing granite can be used not only as cladding (facing) but also as a carpentry stone.

Other interesting variety of granites - rapakiwi (in translation from Finnish literally \"rotten stone\"), is a non-uniform large crystals rock (breed) with plenty of ovoids (from Latin “ovum” means “egg”) - large rounded excretions of pink feldspars (to the bowl of all orthoclase) by a diameter 20...60 mm, surrounded by the white or chlorine borders of plagioclase or quartz. The color of rapakiwi is usually brown-pink and reddish. This variety of granite, widely widespread in Scandinavian countries, characterized by a high decorativeness, however comparatively easily collapses weathering processes and in the group of eruption breeds is the least lasting. Revetment (facing) from rapakiwi was widely used in the Russian town-planning XVIII-XIX centuries and found application in many architecture-historical monuments and buildings of Petersburg - Leningrad and Moscow.

The exceptionally decorative variety of granite is amazonite (= amazon-stone) granite of green and blue-green color, containing in the structure green feldspar - amazonite (on the name of the river of Amazon, where it was first found out).

 

The middle-grained rock (breed) of granite structure - charnockite (in honour sirname  of Charnok, founder of Calcutta, where this rock (breed) received vast distribution as a facing (cladding). Microlite, quartz, pyroxenes, diopside, augite are ingredients of charnockite. Unlike granite, where a dark mineral is biotite or amphibole, in a charnockite it’s a  pyroxenes.

Quartz porphyries and liparites belong to the above enumerated analogues of granites.