There are many different classification schemes for stone. The British Standard BS EN12440 Denomination of Natural Stone addresses classification and insists upon the correct identification of stone type and its origin. However, this is simplified within the UK stone industry and all stones must be considered individually for their merits when used as horizontal surfaces. The main elements of importance to the customer are: is it durable with a limited chance of chipping and breaking in the future following installation; is it durable in relation to the types environment which it will be used in. Typically, a rule of thumb would be that only granite should be used in the kitchen environment due to its strength and resistence to staining, whilst marbles and limestones can be used in bathrooms and for flooring.
The term Granite has been applied to almost any igneous stone that can retain a polish. True granites provide many of these stones but other types that may fall into this calssification include syenites, gabbros, dolerites and diorites. Gneisses and schists are matamorphic rocks that are sometimes included in this category. The formation of igneous rocks (”granite”) is by the cooling of molten materials to form minerals such as quartz, feldspar and hornblende, resulting in a wide variety of colours and grain patterns. The interlocking crystal structure imparts both the high strength and low porosity necessary for a wide range of applications.
The main sources for imported granites are currently Scandinavia, South Africa, Sardinia, India and China. Care should be taken with some of the Chinese stones however. For example, Black Pearl which is commonly traded as a granite is actually lava flow and therefore less dense and more porous than true granite (igneous formation). It will also react and turn white with many household fluids such as wine and lemon. The same is true for China Black “granite”. The consumer should therefore be wary when offered extremely cheap granite in pre-cut “blank” form as these are often only possible to be made in China at a good price due to the cheap labour market. The same rule of thumb should always apply - if in doubt, ask for an off-cut and test it yourself or at least be aware of what you are buying and so take appropriate steps to treat the product more carefully in the future.
