Marble
is a non-foliated metamorphosed rock composed of recrystallized carbonate minerals, most commonly calcite(a crystalline form of calcium carbonate, CaCO3)or dolomite.
Metamorphism causes variable recrystallization of the original carbonate mineral grains.
The resulting marble rock is typically composed of an interlocking mosaic of carbonate crystals.The temperatures and pressures necessary to form marble usually destroy any fossils and sedimentary textures present in the original rock.
Pure white marble is the result of metamorphism of very pure(silicate-poor) limestone or dolostone.It has been very popular for sculpture and building construction because of its beauty and relative softness. It is vulnerable to weathering since its calcium carbonate content is readily attacked by acid rain.
Green coloration is often due to serpentine resulting from originally high magnesium limestone or dolostone with silica impurities. These various impurities have been mobilized and recrystallized by the intense pressure and heat of the metamorphism.
The word "marble" derives from the Greek(mármaros) meaning "shining stone".This stem is also the basis for the English word marmoreal, meaning "marble-like."
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.
Types of Marble:
Some historically important kinds of marble, named after the locations of their quarries,
include:
Carrara | white or blue-gray | Carrara(Italy)
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Pentelicus | pure-white,fine-grained semitranslucent | Penteliko Mounta in, Athens(Greece) |
Ziarat | Pure white | Ziarat Region(Pakistan) |
Macael marble | white | Macael, Almeria(Spain)
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White marbles, like Carrara, have been prized for sculpture due to the softness, relative 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, re sulting in the characteristic "waxy" look which gives "life" to marble sculptures of the human body.
