Marble is a distinctive type of stone made naturally occurred from limestone. Marble as a medium to sculpt statue is appreciated by many of great sculptors. Marble is derived from a Latin word marmar, which has come from a greek word “marmarous” meaning the shining stone. Marble locally in the northern India is known as sangemarmar. The main constituents of marble is calcium and dolomite. The hardness of marble ranges from 2.5 to 5 on the moh’s scale.
a. Dolomite: If it has more than 40% magnesium carbonate.
b. Magnesium: If it has between 5% and 40% magnesium.
c. Calcite: If it has less than 5% magnesium carbonate.
In the earth crust, marbles can be found interblended with metamorphic rocks like phyllites, mica schists, granulites etc. which are in the older layers of earth’s crust and formed due to extreme folding and igneous incursion, in the region of makrana (Rajasthan) the change of limestone’s rich fossils are turned into true marble, which is a common phenomenon in such metamorphic region. White and gray marble which are found different parts of India and also abroad they are in the recrystallized rock form. Many of these places are quarried from 1000s of years and are still in use. Legendary sculpture like Michelangelo and Antonio Canova has used marbles of these region to sculpt extraordinary statue. The purest form of marble also consist of a impurity such as small rounded grains, dark shining flaks of graphite, iron oxides, colorless pale yellow mica and silicate of lime and magnesia. Many of the minerals, semi-precious and gems like biotite, talc, zoisite, chlorite, forsterite, garnet, titanite, spinel, vesusianite, and tourmaline are found in the same layer where marble is found. Due the presence of silicate minerals different colors of marbles are obtained. Green color marble is obtained due to the presence of green pyroxenes and amphiboles, brown from garnet and vesuvianite, yellow color from epidote, chondrodite and titanite, black and gray color from graphite present in marbles. Sometimes interesting patterns may be seen on the marble, when calc-silicate rock bonds with marble and form nodules and patches, marble statue with calc- silicate bonds are hard to finish because of the variation in the hardness between the layers of marble.
The extraction of marble from the mine are done with a limited amount of explosion because usage of too much explosion may shutter the rock. Large channeling machine are used to cut a deep slice into the marble which are about 2 to 3 inch wide, due to the natural cracks present in the marble stone, it is easy to spill into the required size. The large size marble is fed into the saw mills, where they are cut into required size slabs, sets of parallel iron blade cut through marble which moves back and forth, a mixture of sand and water is fed to the blade to ease the cutting process. The marble stone is machined with carborundum wheels for smooth surface and finer grades of abrasive are used for polishing. Throughout the process, even with most high tech machineries, about 50 % of the stone is wasted. Small chunks of marble are used in terrazzo flooring and stucco wall finish.
Identification of marble from other contemporary stone:
1. To identify the stone, make sure its surface is free from grime, dirt and debris by washing it, these impurity may effects in the identification process.
2. Marbles has very smooth and silky and this can be checked by touching the surface of it. If there is any roughness on the surface, then the stone is not a pure marble.
3. Looking at the material from different angle should give out glossy and almost translucent effect. Marbles are high reflective and shiny once polished.
4. Looking at the patterns on the marble gives a idea about the purity of stone. Grains, which runs through the marble, fluid line that create a unsystematic pattern, swirl and smudge of lines. If the stone has crystal like marking and speckles are seen, then the stone is likely to be granite.
5. 100 % pure marble are available in very limited colors, like white, black, grey, cream and red. If marbles are available in colors like bright green, pink and yellow, it is said that, the stone contains impurities.
6. Marbles are heavy compare to its contemporary. By lifting a small piece if marble, the heaviness can be felt. Many time granite are also found as heavy as marble but the identification can be done with the help of textures and patterns.
7. Marbles does not absorb water, so by splashing water on its surface. If the water seeps in, then the stone is not marble.
8. Using a pocket knife scratch the surface of the marble, there should be no or very less mark seen on the surface. If a deep cut can be seen, then it’s not marble.
9. Mable statue generally craved out of single piece, so the base would be always solid and not hollow.
10. By examining the marble with a magnifying glass, if the core is easily visible with fewer marks, it is valued for more price.
11. Brightness of color and symmetry of design also pay’s higher price.