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Materials - Granite

The term granite has been applied to almost any igneous rock or stone of visible crystalline formation and texture that can retain a polish. It is composed of feldspar (usually potash feldspar and oligoclase) and quartz, with a small amount of mica (biotite or muscovite) and minor accessory minerals, such as zircon, apatite, magnetite, ilmenite, and sphene. True granites provide many of these stones but other types of igneous rock that may fall under this classification include syenites, gabbros, dolerites and diorites. The metamorphic stones gneiss, schist and granulite are also frequently included within the classification of 'granite'


Granite is usually whitish or grey with a speckled appearance caused by the darker crystals. However potash feldspar imparts a red or flesh colour to the rock. In more recent years, more colourful and vivid varieties of granite have been discovered which have increased the choices available to architects. Granite crystallizes from magma that cools slowly, deep below the Earth's surface. Exceptionally slow rates of cooling give rise to a very coarse-grained variety called pegmatite. Granite, along with other crystalline rocks, constitutes the foundation of the continental masses, and it is the most common intrusive rock exposed at the Earth's surface.


The relative density of granite ranges from 2.63 to 2.75. Its crushing strength is from 1,050 to 14,000 kg per sq cm (15,000 to 20,000 lb per sq in). Granite has greater strength than sandstone, limestone, and marble and is correspondingly more difficult to quarry. It is an important building stone, the best grades being extremely resistant to weathering.


The interlocking crystal structure imparts both the high strength and porosity necessary for a wide range of applications other than just for flooring; these characteristics are also important in allowing the successful use of slabs that are thinner than other types of stone. Granite is very hard waring and is largely unaffected by erosion, polution or atmospheric attack. Granite facades are usually self cleaning, although panels at eye level benefit from occasional cleaning.


The surface finish affects the appearance of granite and those available include sawn, honed, flame textured, bush hammered and water jet. It is with the gloss polished form, however, that granites reveal fully their colours and grain patterns.


We include here a palette of some of our most popular materials. This display is not extensive as there are many others to choose from that are available to us from worldwide resources.