Building Materials - Table of Contents.........,,,,,,,,,,,,,,,....... Illustrated Architecture Dictionary

Marble


Our Lady of Victory RC Basilica
Sienna Cathedral
Marble comes from limestone that has been compressed and exposed to heat over time.

Marble is granular limestone or dolomite that has been recrystallized under the influence of heat, pressure, and aqueous solutions.

RecrystallizationIn chemistry, recrystallization is a technique used to purify chemicals. By dissolving both impurities and a compound in an appropriate solvent, either the desired compound or impurities can be removed from the solution, leaving the other behind. It is named for the crystals often formed when the compound precipitates out.

Metamorphic:  A striking alteration in appearance, character, or circumstances

US: Most of the white and gray marbles of Alabama, Georgia, and western New England, and that from Yule, Colorado, are recrystallized rocks.

Rome:  Romans started using marble slabs to clad brick and mortar buildings. It was this innovation that allowed them to erect entire marble cities in a short time.

Egypt:   Marble has been found within the tombs of pharaohs and high-ranking officials. Marble vessels were placed within the kings’ tombs that held their organs, including their hearts and lungs, so that they would have them in the afterlife.

In 2018 Turkey was the world leader in marble export, with 42% share in global marble trade, followed by Italy with 18% and Greece with 10%. The largest importer of marble in 2018 was China with a 64% market share, followed by India with 11% and Italy with 5%.


When sedimentary carbonate rocks (such as limestones) are geologically transformed by heat and pressure, the calcite and/or dolomite are recrystallized to form a metamorphic rock called marble. When the original sedimentary rocks are very pure, the result is a white marble, but if impurities are present, colored, banded or veined marble can result. Because of its granular texture, homogeneity and ability to take a polish, marble has been used for sculptures and other artistic purposes for more than 3,000 years.

One of the best known sources of marble is the Apuan Alps in Tuscany in northern Italy near the small port city of Carrara, where numerous quarries have operated since classical times in the nearby mountains. Blocks of marble are brought down from the mountains to the coast at Livorno from whence they are now exported overseas by ship.
- GIA  (online march 2021)


Pure white marble 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.

White marble 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 brings a lifelike luster to marble sculptures of any kind, which is why many sculptors preferred and still prefer marble for sculpting.

Green coloration is often due to ...  silica impurities. These various impurities have been mobilized and recrystallized by the intense pressure and heat of the metamorphism.
Wikipedia (online march 2021)




Examples:
  • Basilica of Santa Croce  Polychromatic mosaic floor

  • Siena Cathedral   The exterior and interior are constructed of white and greenish-black marble in alternating stripes, with the addition of red marble on the façade.

Photos and their arrangement © 2021 Chuck LaChiusa
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