Granite

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Granite

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Granite Physical Properties

Granite rocks are igneous rocks, formed by slowly cooling pockets of magma that were trapped beneath the earth’s surface. Physically, commercial granites are hard, compact rocks with fine to coarse grains of metamorphic or igneous origin. In terms of properties granite is a unique material. The properties lending uniqueness to granite are:
Hardness 6 to 7 on Moh’s Scale
Density 2.6 to 2.8 Kg/cm3
Compressive Strength 140 to 210 N/mm2
Modulus of Rupture 15 to 25 N/mm2
Water Absorption 0.1-0.6%
Average Wear Less then 1%
Porosity Quite low
Weather Impact Resistant

 

 The other properties of Granite are: 

Porosity/permeability
This hard rock has almost negligible porosity ranging between 0.2 to 4%.Thermal Stability
Granite is highly thermal stability and is impervious to weathering from temperature. Even air borne chemicals have no effect on it. It is highly resistant to chemical erosion making granite useful for making tanks to store highly caustic material.Co-efficient of expansion
The co-efficient of expansion for granite varies from 4.7×10-6 – 9.0×10-6(inch x inch).Variegation
Granite has high consistency in color and texture.Hardness
Hardness of granite lends it excellent wear, making it excellent building stone.

Chemical Composition

The chemical composition of granite, by weight percent:
SiO2 72.04% (70-75%)
Al2O3 14.42% (10-15%)
K2O 4.12% (4-6%)
Na2O 3.69%
CaO 1.82% (0.5 – 2%)
FeO 1.68% (1.5 – 3%)
Fe2O3 1.22% (1 – 2%)
MgO 0.71% (0.5 – 2%)
TiO2 0.30% (0.2-0.5%)
P2O5 0.12%
MnO 0.05%

 


Classification

Granite is a common name for all Igneous and Metamorphic Rocks commercially, but geologically “Granite” is a term only for acidic, plutonic Igneous Rock. They can be classified based on Geological and Commercial Value, broadly into three groups.

Genesis – A medium/fine-grained rock of Gneissic structure is available in various colors. Plagioclase, microcline and quartz are the vital minerals, while titanite, biotite, apatite, epidote, zircon and garnet are found in lesser quantities. Small amount of hematite, pyroxene and sericite are also present in this rock, which is of a granitic composition, contains numerous crystallites. Gneisses can be recognized by the wavy patterns or zig zag movements. Others in this category are Paradiso, Kashmir White, Red Multi Color, Madura Gold, Colombo Juprana, Imperial White, Shivakashi Gold, Kuppam Green, Vizag Blue, Lavender Blue, Tropical Green etc.

Porphyry- Some individual crystals known as phenocrysts are bigger than the ground mass, in such cases the texture is known as porphyritic and the granite is called as porphyry. Porphyries are granites which have dominant Feldspar Crystal or Flowers. Tan Brown, Sapphire Blue, Crystal Yellow, Steel Grey, Ruby Red, Cats eye belong to this class.

Dyke- Dykes are the Black Granites, which commonly occurs as Dolerite Dykes. The Black Granites which form a Ring Dyke is a classic example of the Dyke. Other Black Granites or Dykes include Absolute Black in Warangal, Chamrajnagar and other places.

Granite is classified on the basis of the QAPF diagram for coarse grained plutonic rocks (granitoids). They are named according to the percentage of quartz, alkali feldspar (orthoclase, sanidine, or microcline) and plagioclase feldspar on the A-Q-P half of the diagram. A pure granite according to modern petrologic convention consists of both plagioclase and alkali feldspars. When a granite is devoid or nearly bereft of plagioclase, it is referred to as alkali granite. When a granitoid contains <10% of orthoclase it is called tonalite; pyroxene and amphibole are common in tonalite. A granite which contains both muscovite and biotite micas is known as binary or two-mica granite. These granites typically have high quantities of potassium and are low in plagioclase. They are usually S or A-type granites. The volcanic equivalent of plutonic granite is rhyolite. Granite has poor primary permeability but strong secondary permeability.

Application
Granite is widely used as a dimension stone and as flooring tiles in commercial buildings, monuments as well as private houses. Owing to its strength, it is also used as foundations for homes in various countries. With an increase in the number of acid rain in many parts of the world, this rock has begun to supplant marble as a monument material a sit is much more durable. Refined or polished granite is also a popular choice for kitchen counter tops due to its requirement of low maintenance and aesthetic properties. In such cases, “granite” is a common term for all igneous rocks with large crystals, and not specifically to those with a granitic composition. Granite Tiles also finds application for gravestones, memorials and other artifacts. Engineers generally use polished granite surfaces to establish a plane of reference, as they are relatively impervious and inflexible
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