Every stone reveals a part of the Earth’s history. Whether formed from magma or fossil rich sediments, this ancient building material is inextricably linked to our civilisation. Our monuments and great buildings of the past and present still require its timeless beauty, and to that end it is extensively quarried and shipped around the world at great effort and expense. It is no mean feat to cut and process the massive blocks hewn from the earth, even with the colossal machinery used today.
Patterns & Appearance
We use the commercial approach when classifying some stone as marble, when scientifically it is a limestone. It is common for stonemasons and suppliers within the industry to class unmetamorphosed limestone as marble, especially when it takes a high polish. Also differing international standards and industry traditions can confuse classifications, for example some materials are nominated a granite in Asia, when European Standard (EN) states they must be assigned as anorthosite. For reference tables and help identifying stone go here.
Granite – Gabbro – Gneiss – Quartzite – Basalt – Composite Quartz
Formed from the slow or rapid cooling of magma, further metamorphosis and crystallisation can take place to create varied and colourful patterns.
Igneous rocks that have undergone a metamorphosis into a gnessic rock often have a marble-like appearance, the quartzite also exhibits these qualities having undergone a similar process. Colourful ribbons and bands can form creating striking patterns.
Composite quartz is included here as although it is man made, its over 90% quartz and hard to scratch.
Limestone – Marble – Slate – Onyx – Travertine – Sandstone
LIMESTONE – sedimentary rock, mostly the precursor material for marble. As no recrystallization has occurred the ancient organisms and plant life are often still discernible. Easily polished and worked, and very vulnerable to acids.
MARBLE – organisms and plant life over millions of years created enormous sediment deposits in the primordial oceans, as with limestone. Sinking deep into the Earth’s crust, they were subjected to increasing heat and pressure causing recrystallisation. The result is a stone widely sought after by sculptors for their statues, citing its skin like properties and illusion of depth in its surface.
ONYX – a rare crypto-crystalline material, sourced in low volumes. Extremely translucent and available in many colours, the large crystals form a truly unique slab.
TRAVERTINE – sponge-like sedimentary rock requiring extensive filling.
SANDSTONE – sedimentary rock, mainly composed of sand-sized quartz or rock grains. Widely available around the globe, in different grain sizes and colours. Highly compacted, the surface is open, porous and sandy to the touch.
APPEARANCE & PATTERNATION
Another useful way of exploring stones is by their appearance or pattern. They can be a constant, plain colour or have a pattern. The pattern can be further subdivided into uniform-subtle, uniform-bold, irregular-subtle, and irregular-bold.
Constant colour throughout
A grain or fleck pattern is repeated over slab creating a consistent homogeneous look that varies little over one slab.
Pattern is sporadic. One area of material will not necessarily match or align neatly with another area.
Pattern can be sporadic but exists in muted tones.
Significant, vivid structures (sparkling or pearlescent elements, veins, clusters, bands, stripes, ribbons) with strong colouring and crystalline grain, can create a dramatic and striking statement.
|Subtle||A grain or mild pattern, speckles and clusters which easily form continuous joins||Distinctive markings but in muted tones allow flexible placement|
|Bold||Features stand out but occur in regular pattern allowing easy matches||Stong features require careful planning of joints, possibility of bookmatching.|
Two most common types of quarry are hillside and open-pit. Some stone is mined, which is even more difficult and expensive. Three main techniques are employed to remove a block from a deposit; wire saws, rock hammer drills and gallery saws. Explosives are used but have more limited use because of the potential damage to the deposit. They are used in smaller amounts in localised areas or to remove large debris.
Wire saws: Holes are cut into the deposit, through which wires are passed and joined to form a continuous loop. It is tensioned and pulled through by a series of pulleys whilst an abrasive slurry is pumped through, creating a cutting action. Newer technology utilises diamond wire allowing harder stones to be extracted this way.
Rock hammer drills: A series of parallel holes are drilled forming the outline of the desired cut, into which hydraulic wedges are placed to break the block free. Sometimes explosives are used in the holes instead. Large piles of debris are placed below the falling block to lessen the impact. Often used for granites and other hard deposits.
Gallery saw: Resembling a large chainsaw, it pivots at the base and slices through the deposit in much the same manner as a chainsaw would through timber.
Some foliated stone like slate can be split along naturally occurring cleaved planes, by driving steel pry bars into these areas.
Orientation of the cut has little bearing on most stones, but some patterns alter drastically depending on the type of cut. These are referred to as vein cut and cross cut.
The blocks are then cut into slabs by a large single saws, gang saws or wire saws. These slabs are then processed on automated conveyor systems through the various stages of finishing.