Marble is a non-foliated metamorphic rock frequently used worldwide in various applications. Very few rocks have so many uses as marbles. Marbles are used in homes, buildings, construction, roads, sculpting, cemetery markers, and even agriculture.
Marble is mostly composed of the mineral calcite (CaCO3) and usually has minerals like clay minerals, micas, quartz, pyrite, graphite, and iron oxides.
One interesting fact about marble is that the streaks, swirls, and veins on colored marble varieties are due to mineral impurities such as clay, silt, iron oxides, and sand. These impurities were originally present as grains or layers of limestone. The green color in marble is due to serpentine; resulting from magnesium-rich limestone or dolomite with silica impurities.
The pure white marble is created after pure limestone (poor in silicate) is metamorphosed. Pure marble is very rare and costly. One example of white marble is the famous Taj Mahal in India.
Physical Properties of Marble
Marble’s physical properties are of more importance than its chemical composition. Its use is dependent on its physical properties. Hence, geologists and pathologists are more interested in knowing the physical properties.
Marble is found in huge deposits that are 100s of feet thick and extend across a large area, making mining economically viable and production up to millions of tons in a year.
Color: Marble is usually a light-colored rock, but it is also found in bluish, gray, pink, yellow, or black. Colored or pure-white marble is hard to find and costly compared to light-colored marble. The color of marble is due to impurities.
Sensitivity to Acids: Marble is sensitive to acids. The calcium carbonate in the marble neutralizes the acid. This is why crushed marble is often used to neutralize acidic streams, lakes, and soils.
This property becomes visible when you cut a citrus fruit directly on a marble countertop. It leaves a white stain on the marble surface.
Hardness: Marble’s hardness is 3 on the Mohs hardness scale. It is easy to crave and can be shaped into desired sizes for buildings, sculptors, and ornamental objects.
Polish: Marble can be sanded and polished to get shine and luster. It gives a beautiful look to your house.
Marble forms when limestone is subjected to metamorphic heat and pressure. The transformation of limestone from marble usually happens at convergent plate boundaries. Apart from regional metamorphism, contact metamorphism can also make marbles. Contact metamorphism happens when hot magma heats adjacent limestone or dolostone.
The calcite in the limestone is often found in the shape of lithified fossils and biological debris. It recrystallizes during metamorphism, and it changes the rock’s texture. The calcite crystals in the rock are tiny when the transition from limestone to marble begins. The crystals grow larger with time and become recognizable as interlocking calcite crystals. This recrystallization process stops fossil and sedimentary structures of the limestone.
Recrystallization also differentiates marble and limestone. The crystals in the marble grow in size as metamorphism continues. The clay minerals in the marble change to micas and complex silicate structures as metamorphism go on.
The micas and silicate structures may form gem minerals such as corundum that produce ruby and sapphire.
Where is Marble Found?
Marble is found worldwide. The largest producers are Italy, China, India, Spain, Turkey, and Greece. The most valuable white marble is produced in Carrara, Italy. The city is particularly known for its white and blue-gray marble.
- Marble is cut into different sizes to be used as a dimension stone in monuments, buildings, pacing, sculptures, countertops, and flooring.
- Pure marbles with bright colors are crushed, and impurities are removed. The resultant white powder (whiting) is used as a coloring agent, filler, whitewash, cosmetics, plastic, and grout.
- Marble has a low hardness and high solubility, making it ideal to be used as a calcium additive in animal feeds.
- It is also a low-hardness abrasive for cleaning bathroom and kitchen fixtures.
- Marble is the go-to material for stairs for millions of people in the US and worldwide.