Granite, the hard igneous rock Granite is a very hard crystalline, igneous or metamorphic rock primarily composed of feldspar, quartz and lesser amounts of dark minerals. It is visibly crystalline in texture. This igneous rock is created deep within the earth from magma, cooled slowly under great pressure. Granite, the hardest building stone has very dense grain which make it impervious to stain. Granite is available in a wide array of colors. varieties of different colors and textures such as black, grey, pink, multi colored etc. Uses It is used as a building material is used for wall cladding, roofing and flooring and a variety of other interior and exterior applications.
Granite Chemical Properties
Granite is primarily composed of feldspar, quartz along with various other minerals in varying percentage,which are stated as follows:
Nominal chemical composition of various oxides
| Silica(SiO2) |
70-77% |
| Alumina(Al2O3) |
11- 14% |
| Potassium Oxide(P2O5) |
3 – 5% |
| Soda(Na2O) |
3 – 5% |
| Lime |
1% |
| Iron(Fe2O3 |
1-2% |
| Iron(FeO) |
1 – 3% |
| Magnesia(Mg0) |
0.5 – 1% |
| Titina |
Less than 1%(.38%) |
| Water(H2O) |
0.03% |
Granite Physical Properties
In terms of its physical properties granite is a unique material. These properties lending uniqueness to granite are:
Porosity/permeability
Granite has almost negligible porosity ranging between 0.2 to 4%
Thermal Stability
Granite is highly stable thermally, therefore shows no changes with the change in temperature. Granite is impervious to weathering from temperature and even from the air borne chemicals. It is the high resistance to chemical erosion that makes 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 shows consistency in color and texture.
Hardness
It is the hardest building stone and hardness of granite that lends it excellent wear.
Granite, the hard natural igneous rock having visible crystalline texture is formed essentially of quartz and orthoclase or microcline. The principal constituents of granite are feldspar, quartz and Biotite. However the percentage composition of each varies and accordingly impart different color and texture to the final product. The percentage composition of feldspar varies between 65-90% , of quartz can extend from 10 to 60% and that of biotite lies between 10 to 15%.
Varieties of Granite
Granite, a holo-crystalline quartz-bearing plutonic rock, has - 10 to 50% of quartz as its component, the alkali feldspar/total feldspar in the ratio between 65 to 90%, and the modal concentration of other minerals is less than 10%. Cutting of granite follows the processing. The cutting of granite has been made easier by the use of steel abrasives. Use of such tools enhances cutting of granite, saves time and lends smoother edges. The granite is cut into thin slabs by multi-blade gangsaws, and using various types of granite cutting blades available in the market.
Granite is available in three main varieties of granite, which are as follows-
Biotite-granite
Includes quartz, plagioclase, biotite and K-feldspar.
Hornblende-granite
Also called Syenitic granite, contains hornblende as well as mica.
Tourmaline-granite
Composed mainly of Tourmaline, this variety of granite exhibits a wide range of colors and is very rarely available as white or colorless variety.
Of these three varieties, Biotite-granite is most prevalent and forms a very suitable building stone for durability and decoration. These rocks, by reason of their massive nature and homogeneous grain, are eminently adapted for monumental and architectural work as well as for massive masonries. Their wide range in appearance and colors – white, pink, red, grey, black, etc. renders the stones highly ornamental and effective for a variety of decorative uses.
Based on the composition, the color and the make of the granite also varies there are various types of granite comprising of over hundreds of shades. Within India itself there are around 200 shades of granite available. To name a few -Tropical Green Paradiso, Kerala White, Pink and Grey Granite, Monumental red granite which is very coarse, Kashmir White, Tiger Skin, Bash Paradiso, Colombo Juparana, Sea Green, Turaiyur Blue, Hosur Gray, Raw Silk, Ruby Red, Fish Belly, Tumkur Pink, Sira Grey, Savan Rose, English Teak, Hasan Green Tiger Black, Chilly Red, Pista Green, Black Galaxy, Daisy Blue, Blue Pearl, Purplish Granite Porphyry, Mokalsar Green, Silver galaxy, Ivory Shine, Tan Brown, Steel gray, China Pink, Sea weed green, Spotty Black, Chilka Blue, Red Pearl, Spotty Ribbon Gneiss, Deep Pink Granite, American/ Cobra / Emerald Green.
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