White marble is a type of metamorphic rock formed from limestone that's been subjected to intense heat and strong pressure under the Earth's crust. Limestone is a sedimentary rock made of fossil sea shells, corals and diatom (single-cell algae) skeletons. The primary ingredient in limestone is the mineral calcite. When calcite crystals melt and recrystallize into larger, coarser interlocking crystals, the resulting carbonate rock is called marble. Limestone that is free of impurities produces the purest, brightest white marble.
The purest, whitest calcite marble has many properties making it a highly desirable material for fine art statues and sculptures. It was used by the ancient Greeks and Romans to produce classical figurative sculpture. The Italian sculptor Michelangelo used it in all of his statues. The Greeks used it in the Venus de Milo and the famous Elgin Marbles frieze decorating the Parthenon. White marble is relatively soft and easy to work with, using hand tools. It is used in outdoor statuary and monuments due to its lack of porousness, rendering it immune to the freeze-thaw corrosive action of water. The low index of refraction of pure white calcite marble gives it translucent properties, allowing light to penetrate into the stone before being refracted out, giving marble statues a lifelike waxy look resembling human skin.
Pure white silicate-free marble has been used in the construction of monumental architecture since the Egyptians used it to sheath the pyramids for a reflective, shiny effect. It's been prized through the ages for its beauty, resistance to fire, shattering and erosion. The back-scattering effect of white marble was used by classical Greek and Roman architects in the construction of many iconic classical buildings. They appreciated the isotropic (uniform) properties and homogeneity of the stone as well as its ability to be polished to a high shine. Marble can be quarried in huge blocks, making it a primary building material in very large public buildings, such as the Supreme Court, the Capitol building, and the Taj Mahal.
Because of its purity and mineralogical components, white marble has many industrial uses. It's a clean source for most of the world's supply of calcium carbonate. Finely ground calcium carbonate powder is used as a coating pigment in the manufacture of paper due to its brightening and strengthening properties. The powder is also used as food, toothpaste, plastic and paint additives. Since Roman times, it's been heated to produce lime, a primary ingredient of cement.