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Granite |
Granite is
one of the most durable stones, which has been incorporated well
in infrastructures of the present times. The word "Granite" originates
from the Latin word 'granum', referring to the coarse-grained
structure of this crystalline rock. It is composed of quartz,
feldspars and micas, as well as traces of a variety of other
minerals, which contribute to the color and texture of granite.
They are available in pink, dark gray or even black, depending
on their chemistry and mineralogy. A broad range of elegant patterns
and colors makes granite the most versatile of all stones. The
crystal size of the granite is somewhat determined by the rate
at which the granite cools: the slower the cooling process, the
larger the crystals grow. Occasionally some individual crystals
(phenocrysts) are larger than the ground mass in which the texture
is known as porphyritic. Granite is a common and widely occurring
type of intrusive, felsic, igneous rock with great strength and
value. The density of granite is 2.75g/cm3 (avg) and its viscosity
at standard temperature & pressure is ~4.5 . 1019 Pa·s.
Granite is typically the hardest of the dimensional stones and
can withstand the vagaries of nature, effectively. The natural
properties of this stone makes it the real "maintenance-free" stone. |
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Occurrence - Granite
It is widely spread throughout the continental crust of the Earth and
is generously found as a basement rock that underlies in the relatively
thin sedimentary veneer. This light colored Granite Marble Stone often occurs as relatively
small, less as 100 sq. km stock masses (stocks). In batholiths they
are often associated with organic mountain ranges. In some areas very
coarse-grained pegmatite masses are found with granite. Outcrops of
granite usually form into tors, and rounded massifs. Granites also
occur in circular depressions that are surrounded by a range of hills
and are formed by the metamorphic aureole or hornfels.
Granite Tiles - Origin
This versatile rock has been intruded into the crust of our planet during
all geologic periods, though much of it is of Precambrian age. Granite
is an igneous rock which is formed from magma and is currently found
only on Earth where it forms a major part of continental crust. Granitic
magma has many potential origins but it must intrude other rocks. Most
granite intrusions are located deep within the crust, which is usually
more than 1.5 kilometers and up to 50 km depth within thick continental
crust. Small embankments of granitic composition known as aplites are
often affiliated with the margins of granitic intrusions. The origin
of granite is contentious and has led to varied schemes of classification.
Classification schemes are regional and include French, British, and
American systems.
Geochemical Origins
Granite is a ubiquitous component of the crust that has crystallized
from magma and has compositions at or near a eutectic point. Magmas evolve
to the eutectic owing to the igneous differentiation, or because it represents
low degrees of partial melting. Fractional or partial crystallization
serves to reduce a melt in iron, titanium, magnesium, sodium and calcium.
They also enrich the melt in silicon and potassium, which is and alkali
feldspar (rich in potassium) and quartz (SiO2), are the two of the defining
constituents of granite.
This process functions is indifferent to the origin of the parental magma
and its chemistry. However, the composition of the magma which is different
in the final product- granite leaves certain geochemical and mineral
evidence as granite's parental rock. The absolute mineralogy, texture
and chemical composition of the granite is often unique as its origin.
For example, a granite that has been formed from melted sediments may
have a larger portion of alkali feldspar, whereas a granite, which has
been derived from melted basalt may be richer in plagioclase feldspar. |
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 |
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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 4.7x10-6 - 9.0x10-6(inch
x inch).
Variegation
Granite has high consistency in color and texture.
Hardness
Hardness of granite lends it excellent wear, making it excellent building
with granite 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% |
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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 granite 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 granite 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
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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