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Natural Stone Worktop Materials
Worktop surfaces separate into either engineered or natural stone.
Natural stone is cut directly from rocky outcrops in quarries. There are quarries in every country around the world, some more famously known than others. Carrara Marble in Italy and granites from Brazil are probably the better known.
Natural Stone Materials that are used for worktops and other fabricated products are mainly of granite, marble, quartzite, and slate.
How Are They Formed?
Natural stone is formed in several environments, all of which involve high pressure (compaction) and extreme heat. Both heat and pressure are essential to catalyse reactions of natural chemicals and minerals.
The processes that are involved in the formation of the stone that we recognise for natural stone worktops include, crystallization, metamorphosis, lithification and diagenesis.
Environments that are most likely to form rock types are deep in the earth, through the movement of tectonic plates, volcanic activity above and below ground, and ocean floors.
Each different environment will determine the rock type; repeat processes will metamorphose one type into another. As nature recycles itself continuously over uncomprehensible periods of time, through weathering and wearing of existing rocky outcrops.
Weathered grains and leached minerals in combination with the elements, will undergo a larger process termed 'The Rock Cycle'.
Minerals and Crystals
Natural stone formed deep in the earth or through the movement of tectonic plates and volcanic activity above or below ground, will form igneous rock types (i.e. granite) through the cooling of magma or lava.
Rock formed on ocean floors will form sedimentary rock types such as Limestone. The process of metamorphosis can affect all rock types, changing one rock type into another, i.e. Limestone will metamorphose into Marble.
Each metamorphic process increases the mineral content of quartz. The minerals in the environment of the formation of each rock type determine the hardness (mostly that of quartz) of the natural stone.
For example, sediments on ocean floors are a build-up of calcium-rich fecal matter and skeletal remains.
Calcium rich rocks are relatively soft (chalk) and so would be any other rock formed by the same minerals.
Crystallization and diagenesis processes compact and allow crystal growth, strengthening the rock further, additional crystallization processes can strengthen the rock once again to form the hardest known natural stone surface called quartzite.
There are many factors that dictate the eventual cost of natural stone materials in the form of slabs for worktop fabrication.
The clarity and colour of the rock cut from the outcrop can affect the cost substantially; for example, a clean white marble with evenly spaced and desirable veins will be graded as a high end material compared with a marble with an uneven variegated grey background and criss-crossing veins.
The size, thickness and type of the material also affects costs, such as massive granite and quartzite slabs compared to smaller slab sized marble and slate.