A Rapid Guide to Stone Worktop Materials – PART 1

Stone and stone-type materials can be bewildering, even for people involved in kitchen, design or architectural industries. We find it helpful to break things down into natural and reconstituted stones. Many, many stone-type materials are used in homes and gardens, but in our sector the special demands of kitchen use narrow the range a bit. We hope that this two-part guide will shed a bit of light!

PART 1 – Natural Stones

Natural stones which are sold commercially for building, cladding and domestic uses cover a very wide range. Even to begin to describe and classify them in the terms that a geologist would use would immediately confuse anyone else, even granite industry people. On the other hand, simplifying to the point that an ordinary person might understand would immediately create half truths or downright untruths for the geologist. But that is what we need to do, so if you are a geologist, please bear with us! We find this flowchart helpful.

A) Natural Stone

1) Rocks produced from molten rock –
Igneous Rocks

At AG Stoneworks, we try to use the word granite only for stones which have solidified out of molten rock, or magma. A geologist would use the word more narrowly still, but for our purposes, it isn’t a bad simplification. The market isn’t ready for Labradorite, let alone Syenite! These truly igneous rocks are often dark in colour, with small, evenly spread crystalline patterns and no big veins. They are relatively non-porous, and, being dark anyway, staining is not an issue. These stones are very hard and long-lasting, and many of them are familiar as the classic cladding stones used for buildings of quality in our cities. Examples would be Emerald Pearl, Black Pearl, Black Galaxy, Steel Grey.

2) Rocks produced from sediments –
Sedimentary Rocks

Many stones which are often sold under the name granite have not solidified from molten rock. Different broken-up materials settle to form layers which then fuse together to become sedimentary rock. This generally happens in water, and although wind-blown sedimentary rocks exist, they aren’t very relevant to our work.

Sedimentary rocks come, very broadly, in two types: rocks formed from broken pieces of igneous rocks, and rocks formed from fragments of sea shells. The chemical composition of these stones is very different, but both types are important in the building industry.

The real magic when it comes to sedimentary rocks is what happens AFTER they are first formed. Heat and pressure and chemicals leaching through the bedrock all have an effect on sedimentary rocks, producing metamorphic (“form-changed”) rock. Many stones used in our industry are sedimentary rocks that have been transformed in this way.

i) Granulites and Quartzites

Igneous rocks, pounded by water and wind, break down to produce pebbles, shingle, fine grains of sand and even finer dust or clay. When these fragments settle as sediment, they may become stuck together as types of sandstone. Given the action of heat and pressure over time, the grains can fuse together to form many kinds of metamorphic rock.

At the extreme end, quartz grains fuse into large crystal structures. Such quartzites can be very hard indeed, with many of the characteristics of the igneous rocks mentioned above, but are often lighter in colour, with some larger scale veining or pattern. Examples would be Taj Mahal, and Platino and Vancouver from Cosentino’s Sensa range.

Many less dense, more brittle metamorphic rocks are quarried and used in our industry, often under the name granite. Some are granulites and some may be schists, though that is not a term which lends itself to commercial use! These stones are often light in colour, with big or even wild patterns. They are fairly hard but relatively porous, making them prone to sub-surface staining if not carefully sealed. Examples are Colonial White, Ivory Fantasy and Cosmic White.

ii) Marbles and Dolomites

There is a whole family of rocks which are made up from the shells of dead sea-creatures. Like the granulites and quartzites, they are formed by the build-up of sediment, but mainly the Calcium Carbonate of seashells. This in turn may be modified over time through the action of heat and pressure, and by the presence of chemicals in solution moving through the rock. Without the action of heat and pressure, these stones are soft and porous and pretty much useless for commercial use – does anyone fancy a chalk worktop?! But, transformed into the metamorphic rock marble, this kind of stone is one of the most beautiful and sought-after of all.

Marble can be used for worktops, bringing a lustre and a classic Victorian vibe to a kitchen. It is prone to scratching, staining and to attack by household acids; choosing marble means embracing a stone which will change in look over time, and realising that this is part of its charm. Examples would be Carrara, Arabescato and many others.

Some marbles undergo a chemical transformation where the Calcium in their chemical make-up is replaced over time by Magnesium. This makes them harder and less prone to acid attack – which I guess is why the Dolomites are higher than the white cliffs of Dover! One example of a dolomite is Terra Bianca – which is often referred to as a “hard marble”.

If you would like to understand more about these materials or discuss your kitchen, bathroom or media wall project please contact our team for an appointment.