MARBLE ROCK - Marble is a metamorphic stone formed by subjected limestone to heat or pressure. In pure form, marble consists of calcium carbonate (calcite) and is sparkling white. Impurities produce pale gray, brown, or variegated colored rock. Black marble also occurs. Marble takes a high polish. In common usage, any stone that takes a high polish may be called marble, but this is technically incorrect. Marbles aren't made of marble. The toy got its name from its appearance rather than its composition. Ancient toys resembling marbles were made of smooth stone, clay, or nuts.

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Marble Rock

Geology, Properties, Uses

by Anne Marie Helmenstine, Ph.D. 

Marble is a metamorphic rock formed when limestone is subjected to high pressure or heat.

In its pure form, marble is a white stone with a crystalline and sugary appearance, consisting of calcium carbonate (CaCO₃).

Usually, marble contains other minerals, including quartz, graphite, pyrite, and iron oxides.

These minerals can give marble a pink, brown, gray, green, or variegated coloration.

While true marble forms from limestone, there is also dolomitic marble, which forms when dolomite [CaMg(CO₃)₂] undergoes metamorphosis.

How Marble Forms

Limestone, the source material for marble, forms when calcium carbonate precipitates out of water or when organic debris (shells, coral, skeletons) accumulate.

Marble forms when limestone experiences metamorphism. Usually, this happens at a convergent tectonic plate boundary, but some marble forms when hot magma heats limestone or dolomite.

The heat or pressure recrystallizes calcite in the rock, changing its texture. Over time, the crystals grow and interlock to give the rock a characteristic sugary sparkling appearance.

Other minerals in marble also change during metamorphism. For example, clay recrystallizes to form mica and other silicates.

Marble is found all over the world, but four countries account for half of its production: Italy, China, Spain, and India.

Probably the most famous white marble comes from Carrara in Italy. Carrara marble was used by Michelangelo, Donatello, and Canova for their masterpiece sculptures.

Properties

The visible crystals in marble give it a characteristic granular surface and appearance, but there are other properties used to identify the rock.

Marble is considered to be a strong, hard stone, even though its primary mineral, calcite, only has a Mohs hardness of 3.

Marble can be scratched with a metal blade.

Marble tends to be light in color. The purest marble is white.

Marble that contain a lot of bituminous material may be black. Most marble is pale gray, pink, brown, green, yellow, or blue.

Marble fizzes upon contact with dilute hydrochloric acid.

Uses

Because of the way marble forms, it occurs in large deposits worldwide. It's economical to mine this common, useful rock on a large scale.

Most marble is used in the construction industry. Crushed marble is used to build roads, foundations of buildings, and railroad beds.

Dimension stone is made by cutting marble into blocks or sheets. Dimension stone is used to make buildings, sculptures, paving stones, and monuments.

The statue of Lincoln in the Lincoln Memorial is made of white marble form Georgia, while the floor is pink Tennessee marble and the exterior facade is marble from Colorado.

Marble is susceptible to acid rain and weathering, so it wears down over time.

White marble is ground to make "whiting," a powder used as a brightener and pigment.

Powdered marble, along with limestone, may be used as a calcium supplement for livestock.

Crushed or powdered marble is used in the chemical industry to neutralize acid, as a pill filler, and to remediate acid damage in water and soil.

Marble may be heated to drive off carbon dioxide, leaving calcium oxide or lime. Lime is used in agriculture to reduce the acidity of soil.

The Other Definition of Marble

In the stone trade and common usage, any crystalline carbonate that takes a high polish might be called "marble."

Sometimes limestone, travertine, serpentine (a silicate), and breccia are called marble.

Geologists use the narrow definition of a metamorphic rock formed from limestone or dolomite.

Are Marbles Made of Marble?

The original toy called "marbles" bears the mark "Made in Germany."

These playthings were made by rolling clay or another pottery material into balls, then glazing and firing it so that it resembled imitation agate.

The marbles featured round "eyes" from the firing process, giving them a sort of marbled appearance.

Glass marbles entered mass production in 1846, with the German invention of marble scissors.

Toys resembling marbles have been found in excavations of ancient Egyptian and Mesopotamian sites.

Early marbles were rounded stones, nuts, or clay.

While a few marbles are indeed made of marble, the stone is too soft to be an ideal material for the modern game. The name of the toy reflects the appearance of the balls, not their composition.

Key Points

·               Marble is a metamorphic stone formed by subjected limestone to heat or pressure.

·               In pure form, marble consists of calcium carbonate (calcite) and is sparkling white. Impurities produce pale gray, brown, or variegated colored rock. Black marble also occurs.

·               Marble takes a high polish. In common usage, any stone that takes a high polish may be called marble, but this is technically incorrect.

·               Marbles aren't made of marble. The toy got its name from its appearance rather than its composition. Ancient toys resembling marbles were made of smooth stone, clay, or nuts.

Anne Marie Helmenstine, Ph.D.

Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

ThoughtCo and About Education chemistry expert since 2001.

Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

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https://www.thoughtco.com/marble-rock-geology-properties-4169367

 Marble is a crystalline metamorphic rock. In its pure form, it's white. 

Marble caves over General Carrera Lake, Puerto Tranquilo, 

The statue of Abraham Lincoln in the Lincoln Memorial is made of white marble. 

Sometimes polished travertine is called marble. Travertine is a sedimentary rock. 

The original "marbles" were made of glass, not marble.