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GRANITE Coming Together of Beauty, Hardness and Durability

Granite4Plutonic rocks are crystallised from magma slowly cooling below the surface of the Earth. In other words, these rocks form when molten rock cools and solidifies inside the crust of the Earth without erupting to the surface from a volcano. The crystals of different minerals combine giving these stones a mottled appearance; and as the rock cools relatively slowly, the crystals can grow into mammoth sizes.

The most common types of plutonic rock are granite, granodiorite, tonalite, monzonite and quartz diorite. Granites are the best known of the plutonic rocks. They are popular in the stone trade because they can combine beautiful colours with unbelievable hardness and durability. They also take an eye-catching polish. Plutonic rocks that have properties similar to those of granites, such as syenites, diorites and gabbros, are also known as as ‘granite’ in stone industry. A Norwegian syenite called larvikite is one of the most attractive of these stones. These stones contain feldspars that flash with colour as the stones are turned in the light.

Granular and phaneritic in texture, granite is a common type of felsic intrusive igneous rock. The word “granite” comes from the Latin granum, a grain, in reference to the coarse-grained structure of such a holocrystalline rock. Also, the term ‘granite’ applies to a group of intrusive igneous rocks with similar textures and slight variations on composition and origin. These rocks consist mainly of feldspar, quartz, mica and amphibole minerals. These form interlocking somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter colour minerals.

Depending on their mineralogy, granites can be predominantly white, pink, or gray in colour. By definition, granite is an igneous rock with at least 20 per cent quartz and up to 65 per cent alkali feldspar by volume. Granite differs from granodiorite in that at least 35 per cent of the feldspar in granite is alkali feldspar as opposed to plagioclase; it is the potassium feldspar that gives many granites a distinctive pink color.

Lacking any internal structures, granite is nearly always massive, hard and tough. This is why it has gained widespread use among humans, and more recently as a construction stone. Granites are also an increasingly popular choice for practical and hard-wearing surfaces in today’s home. Needless to say, they make wonderful kitchen countertops and tiles for floors and walls.

Ancient Times

Granite3Scholars say that the most famous red granite in the world was first quarried in the third millennium BC. This granite is steeped in history. The red Egyptian granite – granite rosso antico – was extracted at various locations between Aswan and the Shelal district in the Nile Valley of Egypt – and also from islands in the Nile. This red granite was used for interior and exterior claddings and paving; however, it was used in the most important buildings. Massive blocks were extracted for obelisks, columns and sarcophagi. Famous obelisks made of granite rosso antico are referred to as ‘Cleopatra’s Needle.’ They can be seen on the Victoria Embankment in London, Place de la Concorde in Paris and in Central Park, New York. This granite was also sculpted into statues such as the huge figures of King Rameses II in Luxor.

It may be mentioned that most granite rosso antico is coarse-grained with pink or red feldspar crystals, but a very fine-grained variety of rather limited occurrence in veins was also used to some extent. A grey to black granodiorite and stones of intermediate composition come from the same area.

Granite2Here is an interesting fact: A statue of a civil servant called Sekhemka, dating from the fifth dynasty (ca. 2450-2325 BC) was found at Saqqarah, Egypt. Strange as it may seem, this statue, which is now in the Louvre, Paris, is made of granite! Ancient people knew a lot about granite.

Here is another interesting fact about granite: Rajaraja Chola I of the Chola Dynasty in South India built the world’s first temple entirely of granite in the 11th century AD in Tanjore, India.

Modern Times

Those who visit Rio de Janeiro normally admire the famous statue Christ the Redeemer. How many of them notice the beautiful dark rock that forms the plinth of the statue? The plinth is made from verde Ubatuba – an igneous rock from the coastal town of Ubatuba, between Sao Paulo and Rio d Janeiro.

Granite1Verde Ubatuba has large lustrous brownish-green crystals of feldspar, coloured by green orthopyroxene minerals. It is an uncommon type of rock known as a charnockite that was intruded deep in the Earth’s crust during Precambrian times. Charnockites are so highly metamorphosed that in effect they have melted completely and become igneous rocks.

It may be mentioned that demand for Brazilian granites in America has grown by leaps and bounds – especially for the use as kitchen countertops. Being durable and attractive, Ubatuba is one of the most popular granites. It is nowadays frequently used as a construction material for wall dressing, floors and staircases and in the creation of monumental works.

Granite5

In today’s world, granite is extensively used as a dimension stone and as flooring tiles in public and commercial buildings and monuments. Aberdeen in Scotland, which has been constructed mainly from the local silvery-grey granite, is known as the “Granite City.” Granite was commonly used to build foundations for homes in New England mainly because of its abundance. In the 1820s, America’s first railroad, the Granite Railway, was built to haul granite from the quarries in Quincy, Massachusetts, to the Neponset River. Also, granite has begun to supplant marble as a monument material, as it is much more resistant to atmospheric alterations and corrosion caused by acid rain. With its high durability and aesthetic qualities, polished granite has become a popular choice for kitchen countertops.

As polished granite surface plates are relatively impervious and inflexible, engineers have traditionally used them to establish a plane of reference. An unusual use of granite was in the construction of the rails for the Haytor Granite Tramway, Devon, England, in 1820. Granite tables are widely used as a base for optical instruments because of granite’s rigidity, high dimensional stability and excellent vibration qualities.

The curling stone, which is sometimes called a rock in North America, is made of granite. The granite for curling stones comes from Ailsa Craig, an island off the Ayrshire coast of Scotland, and the Trefor Granite Quarry in Wales. The first curling stones were made in the 1750s, the source being Ailsa Craig. Because of the rarity of the granite, the best stones can cost around $1,500. Around 70 percent of the stones used today are made from Ailsa Craig granite.

Ailsa Craig produces two types of granite, Blue Hone and Ailsa Craig Common Green. Blue Hone has very low water absorption – a quality that prevents the action of repeatedly freezing water from eroding the stone. Ailsa Craig Common Green is a lesser quality granite than Blue Hone. In the past, most curling stones were made from Blue Hone but the island is now a wildlife reserve and the quarry is restricted by environmental conditions that exclude blasting.

Today’s Stone Market

Many different granites and other plutonic rocks are available on today’s stone market, which are often supplied by countries such as Brazil, India and China. For example, the ever-growing stone industry gave the name giallo antico to a yellowish granite from the state of Espiritu Santo in Brazil. Other pale granites include Deer Island granite from Maine and blanco cristal from Spain.

A commonly seen Scottish red granite, which is typically suffused pink, comes from the Ross of Muli on the Hebridean island of Muli. Sweden has also produced many red granites.

Popular black ‘granites’ include nero assoluto (premium black) from India, Swedish black from Sweden, Korpi black from Finland and Austral black from Australia. Galaxy black from India, which is beautifully spotted with white, is simply an exquisite work of art.

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