Marble is metamorphic rock. This means that it has undergone a change, much like a caterpillar turns into a butterfly, to reach its present state. Marble begins as limestone or dolomite and is formed by heat and pressure in the earth's crust. The change produced on the limestone and dolomite is called recrystallization. The final form of the marble is determined by the composition and purity of the original limestone or dolomite. Marble may be white, pink, gray, red, or black in color, depending on the impurities in the original limestone or dolomite. The purest calcite marble is white. Marble containing hematite has a reddish color while marble containing limonite is yellow and marble containing serpentine is green.
Mining
Care must be taken when mining marble. It does not split easily in uniform sheets and it may shatter if explosives are used. Marble must be mined by cutting grooves and holes in the rock and separating blocks with wedges. Diamond tipped saws are also used at various stages in the mining process.
Marble is plentiful in the Alabama counties of Talladega, Bibb, Calhoun, Clay, Coosa, Etowah, Lee, Macon, St. Clair, and Shelby. One site in Talladega County is 200 feet thick. Much of the state's marble has been used in buildings all over the United States. Crushed marble also is used for textiles, paints, electrical insulation and plastics.
Uses of marble
Marble has long been highly valued for its beauty, strength, and resistance to fire and erosion. The ancient Greeks used marble in many buildings and statues. The Italian artist Michelangelo used marble from Carrara, Italy, in a number of sculptures. Marble from Tennessee was used in parts of the National Gallery of Art in Washington, D.C. The Lincoln Memorial, also in Washington, was built of marble from Alabama, Colorado, and Georgia.
Extremely pure calcite marble is used for most statues. This kind of marble is translucent--that is, light penetrates a short distance below the surface of the marble before it is reflected. Large blocks of colored marble are used for columns, floors, and other parts of buildings. Smaller pieces of such marble are crushed or finely ground and used as abrasives in soaps and other products. Crushed or ground marble is also used in paving roads and in manufacturing roofing materials and soil treatment products.