Christina Lancaster, age 11, of Ottawa, Ontario, Canada, for her question:
HOW IS COLOR PUT IN MARBLE?
Largest marble quarry in the United States is located in Vermont. This state is also the nation's leading marble
producer. Other states with important marble production activities include Alabama, Georgia, Virginia and Wyoming.
Recently, white marble has lost much of its popularity as a building material but colored marble continues in demand. Marble is any limestone that is hard enough to take polish. It is used for statues, interiors and buildings.
White marble is considered to be the finest of all marbles. All marble is made up of crystals of the mineralscalcite or dolomite. When these are pure, the marble is perfectly white Colored marble comes about when there is the presence of other minerals or small amounts of staining matter mixed with the calcite or dolomite. Black, gray, pink, red, green and many other colors of mottling in marble are used today both inside and outside of buildings and in the construction of monuments.
Red marble is due to tiny particles of hematite between calcite or dolomite crystals. Serpentine marbles are principally green and yellowish green silicates. Fossiliferous marbles are limestones which are full of fossil shells. On polished surfaces of such marbles, the cross sections of the shells can be seen through the rock.
Marble, in a geological sense, is limestone that has been metamorphosed, or changed, through the action of heat far below the earth's surface. Ordinary limestone is made up of fragments of shells or irregular grains of calcium carbonate. But in marble it has been changed to a mass of crystals grown firmly together.
Metamorphism makes marble more uniform in hardness than ordinary limestone. It also has made the marble more uniform in grain pattern and it can be carved better than ordinary than ordinary limestone.
Ancient Greeks made extensive use of marble. Their arcades and temples at Athens and Corinth are monuments to their skill and the materials used. The ancient Greeks used Pentelic marble from Mount Pentelicus, north of Athens, for their finest work. The famous Parthenon, which stands on the Acropolis at Athens, is built of Pentelic marble. The Romans copied the forms of Greek sculpture and architecture and also used marble with great skill.
One of the largest blocks of marble ever quarried came from Vermont. It weighed 93 tons. It was used for a carving on the Oregon Capitol in Salem. The work of art is called The Covered Wagon. An impressive use of marble as a building material can be found in the Supreme Court building in Washington, D.C. The handsome structure was completed in 1935.