Highly valued as a construction, flooring and sculpture material since ancient times, most famously by the Ancient Greeks and Romans, marble is prized for its smooth, soft nature, its strength and purity; it can be found in many countries and is usually associated with refinement and culture, often polished to give a flawless finish. The name marble comes from the Greek word ‘Marmaros‘ which means ‘shining stone’. How is this wonderful material formed?
Marble is a type of metamorphic rock derived from the sedimentary rock limestone (or in some cases dolomite) in which the mineral calcite is present in large quantities. Metamorphic rocks are formed when the original material is subjected to massive amounts of geological heat and pressure in the Earth’s crust over vast periods of time. During this time the original rock undergoes recrystallization where the minerals mould into a new form, changing the texture and geological make-up of the rock (limestone in this case) to form a new type of stone. The temperature to which the rock is subjected makes a difference to how fine the end product is. This is because different minerals recrystallize at different degrees of heat; any impurities in the original limestone will be incorporated into the marble, and will influence its final shade and physical strength. For example, a limestone with silica impurities which is subjected to relatively low temperatures during metamorphosis will produce a marble that has more large crystals of quartz due to the silica needing higher temperatures to ‘melt’, thus a rougher texture is developed. Conversely, a limestone which is subjected to very high temperatures will undergo a process where the quartz crystals end up much finer, and a smoother marble is the result.
The colour or veining in marble also comes from impurities present in the original limestone or those incorporated from surrounding rocks during the metamorphic process. If iron is present, for example, then hematite will be formed within the marble and a reddish brown shade will be visible. If serpentine is present in the limestone, the finished marble will have a green shade to it. Iona marble is famous for this. The most valuable marble used for sculpting is pure white and has a translucent quality. This comes from very pure limestone. Regions such as the Mediterranean, Italy (Carrara marble) or some parts of North America (especially Vermont) are where the finest marbles can be found.
