How Is Carrara Marble Formed?
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Formation by Nature
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This enormous block of crystallized calcium carbonate, known as Carrara marble, originated during the Jurassic era. Over the course of a billion years, the shells of marine organisms had amassed to create limestone. As the earth's tectonic plates merged, the heat, friction and pressure caused the sedimentary limestone to re-crystallize, and metamorphic marble mountains surged from the sea.
The most coveted Carrara marble is the purest white, called statuario, which is 98 percent calcite. Non-calcite minerals such as sand, iron oxide, manganese and clay create colorful veins and streaks in other Carrara marble. These types include bianco (white), arabesco (with gray), calacatta (with tan), cipollino (resembling the onion, with gray and green veins), bardiglio (darker gray) and bianco venato (white with gray). Amid the cavities of the quarries are more than 70 varieties of minerals---wurtzite, quartz, dolomite, calcite, gypsum and fluorite, to name a few.
When first quarried, Carrara marble has a fresh, sparkling quality that inspired the name "la pietra viva," or living stone. At that point, it's also in a much more malleable state for sculptors to form.
Quarrying
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The Romans began quarrying Carrara marble over 2,100 years ago. Initially, stone masons wedged moistened wood blocks into the stone's natural crevices. The wet wood would expand in the crack and release the marble. The process evolved into drilling holes with pickaxes and hammering out the slabs, and then to using handsaws. In the 16th century, explosives were used, and this practice continued until the 1930s. A hydroelectric plant built in 1910 industrialized the area, and in the 1950s, the introduction of diamond-toothed wire saws further refined the process.
Formation by Art
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Michelangelo visited Carrara to pick out his own marble. Following the precept that the artwork actually existed within the stone and his job was to reveal it, he sculpted his masterpiece David from a huge slab of Carrara marble with a mallet and a toothed chisel. (Chisels can also be pointed, round or flat.)
To refine the work, sculptors use files, pumice or sandpaper.
Other masterpieces of Carrara marble include Trajan's Column and parts of the Pantheon facade in Rome, the Marble Arch in London's Hyde Park and the Robert Burns statue in Dumfries, Scotland.
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