Marble

Marble is actually a non-foliated metamorphic rock that geologists refer to as metamorphosed limestone while stonemasons include un-metamorphosed limestone. It has long been the first choice of sculptors and has been widely used throughout history in building projects.

Silicate poor dolomite protoloth, or limestone, creates pure white marble following metamorphism and the marble characteristics of veins and swirls found in many coloured marbles are mostly caused by mineral impurities such as chert, iron oxides, sand, silt or clay. These impurities would have been originally present as layers, or grains, in the limestone. The green colour that is often found in marble is caused by serpentine in the limestone that consisted of high levels of magnesium. Another cause of the green colouring is when the dolomite has silica impurities. These impurities are re-crystalised and mobilised by the heat and intense pressure experienced during metamorphism.

The two Main Uses of Marble

Marble has had two main uses throughout history these being:

White marble in particular has long been favoured for use as sculptures . This is because of its resistance to shattering, its relative homogeneity and uniformity in orientation, as well as its relative softness. It also has a low refraction index that allows light to penetrate several millimetres before scattering. This gives marble its famous waxy appearance that gives a certain “life” to the finished sculpture.

Marble is also a favoured product as a construction material. This type of marble is composed of calcite, serpentine or dolomite and capable of accepting a high polish. Construction industry marble is any crystalline calcitic rock, sometimes non-calcitic rock that is found useful as a building stone. Tennessee marble is a good example. as this is a dense granular fossiliferous Ordovician limestone of a maroon, gray to pink colour.

Most of the world's marble is produced in four countries. These countries; Italy, China, India and Spain providing half the world's demand. Italy produces 20 percent of the world's marble requirements by itself. The others 16, 10 and six percent in that order. The remaining 50 percent is shared among many other countries.

Australia is a substantial marble producer, mostly for domestic needs, with companies such as Penrice in South Australia operating the largest marble and limestone mine in that state. Cairns Marble Australia Pty Ltd sells polished and unpolished slabs of marble. Australia's first marble quarry was established near the Wollondilly River in New South Wales in the 1830's. Only ten years after the river was discovered by Hume and Hovell in 1824. It operated on and off until it finally closed in 1915. Marble is quarried at Maroonah in Western Australia.

Marble quarry operators look for natural joints in the rocks when extracting it from the ground. They must remain extremely careful about where they place the most strain so as to not shatter the stone so that when it is free they can either split it or cut it to the desired size. They use sophisticated machines that channel through the stone rather than resorting to explosives.

Once the stone breaks free it is removed from the quarry and transported on heavy duty trucks to a processing area where it is cut into slabs of appropriate size, depending on the order that has to be filled. Following the initial cutting into a certain size the slab is then textured, polished or honed. Special saws are used to create different shapes, designs and the required finish. Some marble is then finished off by a stonemason tradesman. Marble is very heavy and therefore requires special equipment to be used throughout the processing procedure.