Geologists classify marble as a metamorphic rock, which means it's transformed by heat and pressure over tens of thousands of years. Real marble is mainly composed of limestone or dolomite. The heat and pressure changes its chemical composition over time, and turns it into the marble that we recognize today. The purest marble is white, but it's not uncommon to find marble in various colors or with streaks of other colors mixed in with it.
There are three main types of marble: Carrara, from Italy; Pentilic, from Greece; and Parian, from Turkey. Sculptors revere them for being easily carved and long-lasting, and have used all three of them in famous works. Marble is a relatively soft stone that is easily sculpted. It also tends to hold up well over time. Buildings and sculptures carved thousands of years ago still stand today.
Marble is still used in architecture throughout the world; mainly as a decorative overtone. Ornate marble floors, pillars and fireplaces are symbols of luxury and wealth. Marble has actually been used in architecture for centuries, though. Some of the most notable examples include the columns at the Parthenon in Greece, the interior of the Pantheon dome in Rome and the Taj Mahal in India. Marble was also used often when carving reliefs on the exterior of buildings.
Sculptors have used marble to create some of the most well-known sculptures in the world. Marble's low refractive index and consistency in texture allow "human-like" qualities to shine through. Some notable examples of marble sculptures include Michaelangelo's "David," the "Venus de Milo" and Rodin's "The Kiss." Marble is still used to create sculptures today by modern artists.