Granite is one of the most durable stones. It is formed as a result of magma solidification in the layers of the earth’s crust – at different depths. Major components of granite are feldspar (up to 40%), quartz (up to 35%), mica, and many other minerals. It is feldspar and quartz that give granite a “spotty” color. The stone may have such basic colors as light gray, pink (due to feldspar containing in its structure), yellowish, greenish, and a plethora of mixed shades. Note that “granum” means “grain”, and in Italian “granitio” means “grainy”. The name of the rock says that the structure of granite is grained. When magma is cooled and hardened, crystalline granular rock is formed under the influence of heat and pressure. Actually it is quartz that reveals as glassy grains in granite. Note that the strongest granite is the one that includes more quartz (up to 70%), and the most durable granite is the one that has fine-grained structure.
Granite and its features
You can hear many different statements about the durability of granite. If Russian metaphor “to gnaw the granite of science” is said figuratively, the fact that this stone “lives” more than 500 years is actually confirmed. Moreover, granite is resistant to many external factors such as atmospheric agents, mechanical damage, and even acids. Also, granite is resistant to high and low temperatures (it withstands approximately 300 freeze-thaws). For this rock the coefficient of water absorption is 0.05-0.17 %, which is much higher than that of marble, for example, or any other calcareous rocks. Granite can not be worn away quickly. However, for some types of granite, which are used in everyday life – such as kitchen countertops, or as floor slabs – it is often recommended to apply special treatments to prevent granite from stains and other unpleasant phenomena that can ruin its look.
Granite and its types
There are many types of granite – for example, according to structure differences or color. It should be noted that it is difficult to deduce a common classification, which would be applied not in science, but in practice. The thing is that designers, architects, as well as builders often come across different “types” of granite, offered by suppliers. Traditionally, the gray granites include “Siberian” and «Grey Quenna». Black granites are represented by such rocks as «Absolute Black» and «Nero Africa». Rose-red granite is called «Rosso Marina». Famous white granite is called “Mansurovsky”, yellow one – “Zhiltau” and green one – «Forest Green». If we talk about types of granite according to their structure differences, we should note the following. Plagiogranites have a light gray color, and there is practically no feldspar in their composition. Alaskite is a granite rock of pink (or pink-red) color. In its structure there are almost no minerals, which would give a dark color, but it consists mostly of feldspar. There is also porphyritic granite. Its structure has inclusions of a regular form, i.e. elongated (up to several centimeters). Rapakivi, or “crumbly rock” (in Finnish) is one of the porphyritic granites. Its strength is very low, so it crumbles easily. This is due to the fact that the inclusions of feldspar become overgrown with other minerals. We will not go into details.
How is Granite Mined?
Today granite is mined in several ways. The most modern, expensive and rational method in respect of nature is the use of stone-cutters. A special cut is done in order to remove the stone massif from the earth. Thus, in the extracted blocks there are no cracks, and for granite deposit there is no harm. Granite is also mined with the help of air cushions. First, a special opening is done, into which the tank with high-pressure air is placed. Once the exact location of the breaking is forecasted, something like an explosion follows. This method also prevents the mined blocks from cracks and fissures, but less accurately than the previous one. The oldest way of granite mining is a real blast. Deep down in the rock the hole is made, where the explosive is placed and then blown up. As a result, large clumps break off, but there are cracks in them, and therefore a lot of granite goes to waste. For example, according to statistics, about 70% of the extracted material is used for slabs, and 30% is waste products. Thus, the deposit is consumed irrationally, and granite quality falls. And it falls artificially actually because of the primitive technology, which is still used.
How is granite treated?
Granite is a stone which is easy enough to process. But unlike marble, for example, it is less pliable. Since granite is very strong, cutting and grinding is carried out only with the use of diamond tools. Granite is also polished, which allows obtaining mirror surfaces – but that’s for very sophisticated projects. A rough surface can be created, or it can be polished so that the inclusions of mica could be clearly seen in the texture – it is very beautiful. In order to create granite surface with rough relief, large pieces are cut off the slab surface. To get rough granite surface, heat treatment or diamond tool are also used. Chipped surface will look very natural: it is an imitation of natural splits, cavities in the relief may be up to 50-200 mm. There is also smillage-axed (or bush hammered) work: the surface is evenly rough, but the relief has inequalities of up to 5 mm.
Application of granite with a particular surface has different specific trends. For example, a stone with rough relief is better for facing those parts of the walls, which are applied in the form of individual blocks. Slabs of “rock” type are suitable for the realization of monumental projects with accentuated plinths. Polished granite is an excellent material for small items for interior and decoration, or lining (in the form of tiles). Polished or glazed surface is good for finishing the exterior surfaces with large areas (terraces, plinths, parapets, etc.).
Application of granite
Granite is considered to be a versatile material, as its strength and beauty make it possible to use it in the creation of various projects. For example, it is used in the decoration of the walls and floor inside the building. Stairs and steps made of granite look very natural, but it’s better not to choose polished surface, because it is slippery. Granite windowsills and countertops are perfect for any style of interior. In particular, different mosaics and panel pictures laid on the floor look beautiful. If granite is used indoors, it is well combined with other materials such as art forging, glass and ceramics, metal and even wood. Handmade products will look very good against background of this natural stone. Besides, in the design the most valuable are the granites of dark red, greenish-blue and light blue colors.
In addition to the external cladding of buildings (caps for example), terraces and parapets, granite is used for the creation of original projects of landscape design – for example, in the facing of fountains, small architectural forms. In ancient Rome the granite paving stone was very popular. Perhaps, such paths will look very presentable in any garden. Crushed granite is used In the construction. Do people build houses entirely of granite? Perhaps the only known example is a palace of El Escorial (near Madrid), which is already 450 years old.