Information of Marbles :

Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble may be foliated. Geologists use the term “marble” to refer to metamorphosed limestone; however, stonemasons use the term more broadly to encompass unmetamorphosed limestone. Marble is commonly used for sculpture and as a building material.

Uses

Sculpture

White marbles has been prized for its use in sculptures since classical times. This preference has to do with its softness, which made it easier to carve, relative isotropy and homogeneity, and a relative resistance to shattering. Also, the low index of refraction of calcite allows light to penetrate several millimeters into the stone before being scattered out, resulting in the characteristic waxy look which gives “life” to marbles sculptures of any kind, which is why many sculptors preferred and still prefer marbles for sculpting.

Construction marble

Construction marble is a stone which is composed of calcite, dolomite or serpentine which is capable of taking a polish.More generally in construction, specifically the dimension stone trade, the term “marble” is used for any crystalline calcitic rock (and some non-calcitic rocks) useful as building stone. For example, Tennessee marbles are really a dense granular fossiliferous gray to pink to maroon Ordovician limestone that geologists call the Holston Formation.

Ashgabat, the capital city of Turkmenistan, was recorded in the 2013 Guinness Book of Records as having the world’s highest concentration of white marbles buildings.

Production

According to the United States Geological Survey, U.S. domestic marbles production in 2006 was 46,400 tons valued at about $18.1 million, compared to 72,300 tons valued at $18.9 million in 2005. Crushed marble production (for aggregate and industrial uses) in 2006 was 11.8 million tons valued at $116 million, of which 6.5 million tons was finely ground calcium carbonate and the rest was construction aggregate. For comparison, 2005 crushed marble production was 7.76 million tons valued at $58.7 million, of which 4.8 million tons was finely ground calcium carbonate and the rest was construction aggregate. U.S. dimension marble demand is about 1.3 million tons. The World Demand for (finished) Marble Index has shown a growth of 12% annually for the 2000–2006 period, compared to 10.5% annually for the 2000–2005 period. The largest dimension marbles application is tile.

In 1998, marbles production was dominated by 4 countries that accounted for almost half of world production of marbles and decorative stone. Italy and China were the world leaders, each representing 16% of world production, while Spain and India produced 9% and 8%, respectively. Italy is the world leader in marble export, with 20% share in global marble production, followed by China with 16%, India with 10%, Spain with 6%, and Portugal with 5%.

Occupational safety

Dust produced by cutting marbles could cause lung disease but more research needs to be carried out on whether dust filters and other safety products reduce this risk.

United States

The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for marble exposure in the workplace as 15 mg/m3 total exposure and 5 mg/m3 respiratory exposure over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 10 mg/m3 total exposure and 5 mg/m3 respiratory exposure over an 8-hour workday.

Physical origins

Marble is a rock resulting from metamorphism of sedimentary carbonate rocks, most commonly limestone or dolomite rock. Metamorphism causes variable recrystallization of the original carbonate mineral grains. The resulting marble rock is typically composed of an interlocking mosaic of carbonate crystals. Primary sedimentary textures and structures of the original carbonate rock (protolith) have typically been modified or destroyed.

Pure white marbles is the result of metamorphism of a very pure (silicate-poor) limestone or dolomite protolith. The characteristic swirls and veins of many colored marble varieties are usually due to various mineral impurities such as clay, silt, sand, iron oxides, or chert which were originally present as grains or layers in the limestone. Green coloration is often due to serpentine resulting from originally magnesium-rich limestone or dolostone with silica impurities. These various impurities have been mobilized and recrystallized by the intense pressure and heat of the metamorphism.