Home' Inclean : INCLEAN May-Jun 2016 Contents 40 INCLEAN May/June 2016
By Garry Phillips*
There are two common misconceptions
about stone: firstly, that all natural stone
is the same; and secondly, that all natural
stone is maintenance-free.
What is natural stone?
Interestingly, a stone is essentially a
collection of minerals in solid form, and
the way that stone is formed has a lot to
do with the way it behaves.
Whether it has been 'cooked' in the centre of the earth
(metamorphic); erupted from a volcano and solidified by cooling
(igneous); or simply pressed together over thousands of years
(sedimentary); each piece of stone has been through a lengthy
natural development process before it enters our homes or offices.
Understanding the background of a type of stone improves
understanding into why it has certain problems or characteristics,
and how it should be treated so that it will last for many more years.
There are three main ways that natural stone is formed, and this
affects the characteristics of the subsequent piece of stone that is
mined for use by man.
Sedimentary stone is perhaps the most simple, and yet possibly the
lengthiest, way that stone is formed. Over thousands or even millions
of years, pebbles, sand, pieces of older stone, and often fossils are
pressed together, gradually compacted by the growing layers of
sediment accumulating each century. Eventually the weight will
compress these loose items into a single piece of stone. The process
can also occur with the rapid evaporation of a body of water.
Common sedimentary stones include sandstone and limestone. By
nature, sedimentary stones are porous as the force of the weight that
creates them is not sufficient to force the particles to join together
smoothly. Sedimentary stones are also usually quite soft -- as no
chemical reaction has occurred to produce sedimentary stones, the
particles are still individual and are not 'bonded' together as with the
other stone types.
Igneous stone is less common, as the method for its formation
relies on volcanic eruption. As a result, most of the igneous stone
that we use today is incredibly old, having been formed when the
Earth was more volcanically active.
When a volcano erupts, the molten magma makes its way out
of the core and onto the surface of the earth. Over time and with
exposure to air, the magma crystallises. Igneous rock can be coarse-
grained (as in granite), fine, or glassy. During cooling it sometimes
occurs that certain areas solidify faster than others, causing the
parallel bands of flow texture you can see in some igneous stones.
Basalt and granite are the most common types of igneous rock.
Metamorphic stone is the least visible way that stone is formed, as
it occurs at great depths within the core of the Earth. A combination
of heat radiating from the core, and high pressure generated by the
weight of the Earth above, causes stone to change in structure and
texture from its original form.
The initial ingredients of metamorphic stone may have been
anything -- the metamorphic process can transform many kinds of
stone from within the earth's crust -- so the characteristics will vary
based on what the stone used to be.
The most status-filled stone, marble, is derived from limestone that
is subjected to the metamorphic process. Therefore marble is porous,
like limestone, however to a slightly lesser degree. Marble is soft, like
limestone, however the softness varies depending on the purity of
the marble and how many other minerals have been involved in the
metamorphic process (the presence of other minerals is what gives
marble its colour -- pure marble is completely white).
What does this mean for maintaining stone?
The way that stone is formed will affect its porosity, hardness, and
density as well as the aesthetics of how it looks, so it's useful to
understand the stone's characteristics before you decide where or
how to use it in your property.
With this understanding, it becomes clearer how the stone should
be cleaned, whether it should be sealed, and what is most likely to
cause damage to the surface.
In the next article I will discuss sealers and coatings for different
types of natural stone.
*Garry Phillips is 'The Tile Expert' www.thetileexpert.com and
founder of Slique International and Tile Cleaning Products,
Natural Stone -- eternal style, or eter nally stained?
Heat and Pressure
Heat and Pressure
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