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The geology of granite
Granites are coarse-grained igneous rocks, solidified from molten lava, which have cooled and crystallised at great depth within the earth (some granites are metamorphic in origin, but these types are less important in the ornamental stone industry). Because they cooled at depth, granites have cooled slowly and their individual mineral crystals have had time to grow large, so today we see them as coarse grained rocks with a granular, interlocking mineral texture. The deeper they formed, the larger the size of the grains making up the granite rock, and the more attractive they can be as ornamental stone samples. Granites are usually formed of grains of quartz, feldspar and mica, but often with other minerals in small quantities as well. This combination of pale and dark minerals gives the granite a characteristic "spotty" or mottled appearance. Because they contain a high percentage of quartz grains (which are hard and resistant), granite is normally a hard and durable rock type which weathers very slowly. For this reason, areas of granite often form resistant hills and mountains. This quality also makes granite a durable and long-lasting ornamental stone. After formation, granites (like all other rocks) are frequently subjected to deep-seated, earth moving pressures (eg. Mountain building, also called orogenesis), which can cause natural changes to the original granite rock. These changes may include new alignments of mineral grains, irregular colour changes, jointing, and mineral veining (eg. With quartz and calcite), which adds to the natural visual variation in the rock.
Granites are natural materials, and as such are inherently variable in shade and colour. No guarantee can be given that the product will be uniform, or indeed the same colour as depicted in the showroom or in samples.
How is granite processed?
Granite is quarried by means of excavation. Once a quarry is found, research is done on the material primarily to ascertain how many tons or cubic metres of material there may be in the quarry and as to whether it would be economically viable for the material to be quarried and brought to market.
In the quarry, bore holes are drilled and cutting cables are fed into the holes. These cables cut different faces of the granite into large blocks of approximately 3 metres in length by 2m in width and 2m in height. The size of a mid sized van or large 4 X 4. The blocks are then loaded and transported to processing plants all over the world. At these highly automated processing plants, the blocks are cut into slabs often 3cm and 2cm thick. They are then put through polishing lines or different types of finishing lines. Once the polishing process is finished the slabs are inspected and put into bundles. These bundles are crated and shipped all over the globe to importers and stockist. It is from these stockists that we purchase our granite slabs which eventually end as kitchen worktops.
What is a slab?
In the world worktops a slab is a sheet of granite, marble or engineered stone. Slabs are normally quite large and require special handling equipment to move them as they are heavy and can break easily.
Thickness – how thick do the materials come in?
Granite and marble material for worktops normally comes in 2cm and 3cm thicknesses. Engineered stone also comes in 2cm and 3cm thickness, however some manufacturers do supply 1cm slabs as well.
How many types of granite are there?
There are many types of granite. Granite comes in many different colours. It is impossible to say how many types of granites there are, as new quarries are coming on line all the time, as well as old quarries dying out. Suffice to say that there are so many types now that most people can find a type of granite to their liking.
How strong is granite?
Granite is very strong if carried in the vertical. However it is not strong when transported flat or in the horizontal. It is very durable and hardwearing and ideal for kitchen worktop surfaces. In worktops, the strength of granite is weakened with the number of cut outs and holes that are put in it.
Does granite bend?
Yes it does! Very slightly. If you have a large piece of granite lying flat and try to lift one corner very delicately, you will see that the granite flexes. So yes, it does bend.
Does granite scratch?
Even though granite is very strong, it can scratch. Some granites scratch more than others. To avoid scratches on your granite tops, use cutting boards as you would normally do with non granite worktops.
Does granite stain?
Yes it does! Some granites stain less than others and some more than others. To avoid staining, make sure your worktops are sealed when fabricated and then make sure that you maintain them and seal them on a regular basis.
How much does granite cost?
Granite costs vary a great deal. It is a sought after material and its price is mainly determined by the supply available, the demand for it, and the distance it has to travel to market. The main point to keep in mind when choosing granite worktops is that one component of the cost of granite work-tops is the granite itself. The templates that need to be made, the cutting, edge polishing, tap holes, sink cut outs, hob cut outs, etc. delivery and installation are all more or less equal across all materials. So just because one granite might be twice the price of another does not mean that the overall price will be double too. It is only the granite cost in the quotation that is more, not the rest of it. In a nut shell, the bigger the kitchen the bigger the difference in price between two granite types. |