Before you is a beautiful marble Italian Renaissance-style fountain in the roundabout in front of the Barber Marina. Although it's not an exact replica, it was influenced by the Neptune Fountain in Rome, Italy. The marina and the surrounding outdoor art was commissioned by billionaire philanthropist George Barber, and the fountain is one of the highlights of the marina. The marble fountain is the subject of this EarthCache lesson.
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Marble is a metamorphic rock that mainly consists of the mineral calcite (a crystalline form of calcium carbonate CaCO3), which means that the stone contains primarily calcium, carbon and oxygen. The stone is widely used as a material for sculptures and buildings, and also has a number of other uses, including as countertops in homes, as cemetery markers, as construction aggregate, as a whitening agent, and for soil treatment.. There are large deposits of marble in Italy, Spain, India, and China; and one of the largest producers of marble in the United States is only 200 miles north of here outside of Birmingham, Alabama.
In art history and archaeology, marble is also used as a term for other types of stone used in sculpture and architecture, including sandstone and granite, but geologists only recognize true marble as being made from limestone or dolomite. There are many types of marble, each with distinct surface characteristics, texture and color, including Creole, Carrara, Parian, Yule, Vermont, Pentelic and Etowah marble, among many others.
Marble is formed when the sedimentary rocks limestone or dolomite melt and then harden again, which means that marble is a metamorphic rock. The starting point can, for example, be deposits on the seabed of shells, shellfish, and other marine organisms that have petrified into limestone. The temperature and pressure required to form marble usually destroys any fossils and sedimentary texture in the original rock. Marble is soft (3 on Mohs hardness scale, compared to Gold and your fingernail, which is slightly softer at 2.5), is easy to shape with tools, and is perfect for sculptures and monuments.
Colors:
- Pure, white marble is formed by metamorphosis of very pure limestone. The characteristic veins on many colored marble varieties usually come from impurities in the minerals, clay, sand, silt or iron oxide that were present in the original limestone.
- Green color often comes from serpentine from limestone with a high content of magnesium or dolomite with silicon impurities. Copper also gives a green color.
- Pink color comes from manganese.
- Black comes from iron oxide.
- The mixture of colors in the marble comes from the fact that the pure limestone was contaminated by various minerals.
Properties:
- Marble is most often white (egg white) occasionally with impurities of veins and other colors.
- Marble has visible crystals (occasionally larger than 1mm)
- Marble can be flaky
- Marble is soft and can be scratched with a knife or harder stone.
Carrara Marble is one of the world's most famous types of marble, and has been prized for its color and beauty as a building material for thousands of years. It comes from the quarries around the town of Carrara in Italy, in the north of the Tuscany region. The marble quarries are located in the Apuan Alps, mainly in four valleys (Valle di Torrano, Valle di Misseglia, Valle di Bettizano, Valle di Colonnata) around Carrara. Most of them are located at approximately 3,000 feet in elevation. The oldest of the mines date back to 200 BC.
Marble from this area of Italy was in high demand during the Roman Empire for public buildings and statues. Many famous sculpters used Carrara marble in their work, including Michelangelo, Bernini, Pisano, Donatello and Canova. Carrara marble was used for the Pantheon, Trajan's Column, and the Column of Marcus Aurelius, all in Ancient Rome. It was also used in the Marble Arch in London (England), the Victoria Memorial in London, the famous Sarcophagus of St. Hedwig-The Queen of Poland in Kraków (Poland), First Canadian Place in Toronto (Canada), the Sheikh Zayed Grand Mosque in Abu Dhabi (UAE), many of the Harvard Medical School Buildings in Boston (Massachusetts, USA), the Oslo Opera House in Oslo (Norway), in the Normandy American Cemetery and Memorial in Normandy (France), the Peace Monument in Washington, D.C. (USA), the King Edward VII Memorial in Birmingham (England), the Swaminarayan Akshardham in Delhi (India), the Aon Center in Chicago (Illinois, USA), the Milwaukee Art Museum in Milwaukee (Wisconsin, USA), the Devon Tower in Oklahoma City (Oklahoma, USA), the Leaning Tower of Pisa in Pisa (Italy), in St. Peter's Basilica in Rome (Italy), in the former World Trade Center in New York City (New York, USA), the Rotunda at the University of Virginia in Charlottesville (Virginia, USA), the General Grant National Memorial in New York City (New York, USA), the Saadian Tombs in Marrakesh (Morocco), as well as in many casinos in Las Vegas and countless churches and cathedrals around the world.
Carrara marble has been designated by the International Union of Geological Sciences as a Global Heritage Stone Resource.
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Weathering is the breakdown of rocks and minerals under the influence of external forces. Weathering is divided into chemical and mechanical weathering.
Chemical weathering occurs when chemical reactions occur between water and the minerals in the rock so that the mineralogy changes. There are three types of chemical weathering:
- Dissolution: water acts on the stone material and the minerals are dissolved in the same way as we dissolve salt in water (or sugar in tea!).
- Oxidation: a substance reacts with air and loses an electron in the same way as when iron rusts.
- Hydration: a substance reacts with water and new minerals are often formed - especially clay minerals.
- Carbonation: carbon dioxide from the air or soil sometimes combines with water in a process that produces a weak acid, called carbonic acid, that can dissolve rock.
Mechanical weathering takes place when various physical forces act on the rock and break it down. During mechanical weathering, the rock and rock material crack and break into smaller parts without changing the mineralogy. There are several types of mechanical weathering, which include:
- Thermal Stress, or Solar Blasting is a form of mechanical weathering. The bedrock is exposed to temperature fluctuations over the course of a day. This daily change of the mineral grains in the rock can cause the outermost layers to slowly break into pieces.
- Frost cracking happens when water flows down into the bedrock and freezes. The volume then increases, and this results in such a great pressure that the rock can crack. The explosive force is due to the fact that water expands by 9% when it freezes. Frost weathering only becomes effective when the temperature drops to minus 5-6 degrees. There is not much chance of Frost cracking in the climate here.
- Haloclasty, or Salt Blasting happens when dissolved salt in water can crystallize and open pores in the rock. When heated, the salt expands and the rock experiences stress from within.
Weathering and People: Weathering is a natural process, but human activities can speed it up. For example, certain kinds of air pollution increase the rate of weathering. Burning coal, natural gas, and petroleum releases chemicals such as nitrogen oxide and sulfur dioxide into the atmosphere. When these chemicals combine with sunlight and moisture, they change into acids. They then fall back to Earth as acid rain. Acid rain rapidly weathers limestone, marble, and other kinds of stone. The effects of acid rain can often be seen on gravestones, making names and other inscriptions impossible to read. Acid rain has also damaged many historic buildings and monuments.
To log this cache, you must visit the posted coordinates and answer the questions below:
- Study the marble up close - is this marble pure white, indicating very pure limestone, or does it have veins indicating impurities while the marble was being metamorphosed from limestone?
- What weathering can you see on this fountain?
- Study the colors...which mineral do you think is the cause of the colors you see here?
- Take a photo (required) of you, your group, or something that identifies you with the fountain in the background.
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Sources:
The Illustrated Guide to Rocks & Minerals by John Farndon, 2018
Minerals from Marbles of Carrara and the Apuan Alps by Vicchio di Mugello, 2019
Marble and Other Metamorphic Rocks by Chris & Helen Pellant, 2007
Classical Marble: Geochemistry, Technology, Trade by N. Herz and Marc Waelkens, 1988
Rock Identification Field Guide by Patrick Nurre, 2014