What is a Natural Stone?
Composition
Natural stones are formed as a composite of pure mineral elements and almost always involve more than one mineral type. They are classified using names – such as ‘Marble’, ‘Quartzite’, ‘Granite’, etc – that help us understand their generally accepted properties.
Classifications indicate: predominant mineral type(s), method of formation, and typical property analysis but, owing to vagaries of etymology – by geography, environmental happenstance, or era – each individual stone also brings with it a history uniquely its own.
While every natural stone categorised by ‘type’ – as in ‘marble’, ‘granite’, etc – will have compositional structure, formational history, and properties that are essential to their parent category, each stone will also have degrees of porosity, fragility, tonality, etc, according to its own blueprint for how it came into existence.
The beauty of any stone slab will equally vary according to the eye of its beholder. What is always true is that whatever natural stone may find its way into a kitchen or bathroom design, it will always – by its very nature – be essentially, necessarily, unique.
Types of Natural Stone
1. Sedimentary
- Sedimentary rocks form when mineral deposits are compressed and fused together over time and under the weight of new deposits above them.
- Examples: Limestone, Sandstone, Travertine.
2. Igneous
- Igneous rocks are formed from molten rock (magma) that has cooled and hardened. They are either intrusive (formed below the earth’s crust) or extrusive (formed near to or above the earth’s surface as a result of volcanic activity).
- Intrusive igneous rocks are often granular in appearance, because they are more likely to cool slowly and form visible crystals as they do so. Extrusive rocks, by contrast, are typically fine-grained, because they have cooled relatively fast.
- Examples: Granite (Intrusive); Obsidian – ‘volcanic glass’ (Extrusive)
3. Metamorphic
- Metamorphic rocks are formed from pre-existing rocks (sedimentary or igneous) that have been transformed via exposure to extremes of heat and pressure – typically caused by tectonic action (movement of the earth’s plates) or magma flow. These rocks are often hard and/or dense and can be polished to a sheen.
- Examples: Marble (from limestone), Quartzite (from forms of sandstone).
What is an Engineered Stone?
Engineered stones are man-made composite constructions manufactured from a mix of different ingredients. Some are purely mineral based (eg Porcelain and Sintered Stones), others may contain greater or lesser amounts of minerals combined with resins to help bind them together (eg Quartz).
Heat, chemicals, and forms of pressure may be added or applied to help bond these stones, and pigments will be used to create markings that mimic a variety of materials, including natural stone.
Engineered stones are often known by their Brand names, and vary in quality, size and composition depending on the practices of their individual manufacturers.
The patterning of an engineered stone may be utterly predictable or unique to each slab or tile. Because the manufacturing process is controlled, they are – in general – more easily able to be uniformly and exactly described in terms of their size, patterning and essential properties than natural stones.
Many engineered stones are exceptionally heat and water resistant and relatively scratch resistant, although any material that contains resin as a bonding agent may be vulnerable to discolouration from exposure to UV rays.
Properties of Stone Surfaces
Durability, Sustainability, and Hygiene
Hardness: is a common yardstick by which the durability of stone is measured. It is assessed according to the Mohs scale which runs from 1 (softest: talc) to 10 (hardest: diamond). This scale represents a means of measuring mineral elements against each other in terms of ‘scratch-ability’, rather than toughness or other forms of durability: stones that register at a lower end of this scale are thus measured by their vulnerability to scratching by those that register at higher levels.
Porosity: affects ‘stainability’, water resistance and hygiene – the lower the porosity the less likely a stone is to stain, to absorb water, or to harbour germs.
Porcelain: a hard, enduring, engineered stone (registers approx 7 on the Mohs scale) with low porosity. A polished ‘gloss’ finish (left) is likely to show scratches unlike its matt finished equivalent (right)
A high degree of hardness does not necessarily correlate with how well a stone will perform as a water resistant or germ resistant surface, or even if its surface can be scratched (which may also depend on finish).
A ‘hard’ surface may still be vulnerable to staining and harbouring germs (because it may still be porous), although it can be sealed to help minimise porosity. A ‘soft’ surface, contrariwise, may be easily scratch-able, but may also be stain and germ resistant.
For example, Soapstone – composed in large part from talc – registers low on the Mohs scale but is a hydrophobic material – meaning it will repel water – so, while it may be easily scratched, it will not absorb stains or hold onto bacteria and other germs.
What you lose on the swings, you may gain on the roundabouts – it’s all a matter of priorities and which properties you value most – different properties may suit different areas or tasks within any given kitchen.
Property Alerts
Density
A dense stone is more likely to absorb and retain heat evenly and to radiate it outwards. It will have insulating properties and be more resistant to thermal shock. Porous stones can absorb and retain heat, but will also be more inclined to thermal shock.
Thermal Resistance:
The degree of thermal resistance of any given mineral or stone is what enables it to withstand extremes of temperature. However, even the most thermally resistant surfaces may still be subject to the damaging effects of thermal shock – we nearly always caution the use of heat protective mats/trivets when placing hot pans on cool surfaces!
UV Resistance: natural stones formed from minerals are normally not affected by the damaging effects of UV light; engineered stone, by contrast, may contain resins as binders, and these may discolour under strong UV light.
Fragility: will depend on the mineral and structural combination of each stone. Stones that are comprised of layers of different minerals may be vulnerable to fracture or repair along these lines of structural change. No stone surface, whether natural or engineered, is entirely ‘bomb-proof’. And even the most flexible, durable, and resistant stones can be vulnerable to cracking, to chipped edges, to damage caused by thermal shock or to damage from direct impact from a heavy object.
Slab Sizes
Will vary for natural and engineered stones, bear in mind that sometimes a seam or join will be necessary, and sometimes a slab size may help dictate the length of a run (particularly for natural stones the markings of which may be pivotal to a design)
After Care
The care instructions we provide advise on how best to avoid unnecessary damage, how to keep the surfaces clean, hygienic, and well maintained, and if and how repairs or re-polishing can be undertaken.
‘Wabi-Sabi’ and Stone
Wabi-Sabi is a concept that derives from Japanese traditions in finding beauty – by embracing ageing, imperfection, impermanence, and humility, as essential elements of life in all its seasons.
Every stone surface will age in place according to its own history and circumstances: it may always be better to learn to embrace the beauty of the patina and scratches that are the marks of time and loving use than to aim to resist their inevitability.
“Every scratch tells a story” has long been the mantra in our showroom, where our working surfaces, kitchens and displays are put to regular use and demonstrate their subtly shifting transformations as we put them through the paces of everyday living.
