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Calcite |
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Calcite is one of the most important minerals. It is extremely common and
found throughout the world in sedimentary, metamorphic and igneous rocks. In
the form of limestone and marble it makes up a significant portion of Earth's
crust and serves as one of the largest carbon repositories on our planet. The
properties of calcite make it extremely useful as: construction materials,
abrasives, agricultural soil treatments, construction aggregates, pigments,
pharmaceuticals and more.Calcite as Limestone and MarbleLimestone is a sedimentary rock that is composed primarily of calcite. It forms from both the chemical precipitation of calcium carbonate and the transformation of shell, coral, fecal and algal debris into calcite during diagenesis. Limestone is also formed as a deposit in caves from the precipitation of calcium carbonate. Marble is a metamorphic rock that forms when limestone is subjected to heat and pressure. Uses of Calcite in ConstructionThe construction industry is the primary consumer of calcite in the form of limestone and marble. These rocks have been used as dimension stones and in mortar for thousands of years. Limestone blocks were the primary construction material used in many of the pyramids of Egypt and Latin America. Today, rough and polished limestone and marble are still used in prestige construction. Modern construction uses calcite in the form of limestone and marble to produce cement and concrete. These materials are easily mixed, transported and placed in the form of a slurry that will harden into a durable construction material. Concrete is used to make buildings, highways, bridges, walls and many other structures. Uses in Acid NeutralizationCalcite has numerous uses as a neutralizer of acids. For hundreds of years, limestones and marbles have been crushed and spread on fields as an acid-neutralizing soil treatment. They are also heated to produce lime that has a much faster reaction rate in the soil. Calcite is also used as an acid neutralizer in the chemical industry. In areas were streams are plagued with acid mine drainage, crushed limestone is dispensed into the streams to neutralize their waters. Calcium carbonate derived from high purity limestones or marbles is also used in medicine. Mixed with sugar and flavoring, calcium carbonate is made into chewable tablets used in the neutralization of stomach acids. It is also an ingredient in numerous medications used to treat digestive and other ailments. Calcium Carbonate SorbentsSorbents are substances that have the ability to "capture" another substance. Limestone is often treated and used as sorbent material during the burning of fossil fuels. The calcium carbonate reacts with sulfur dioxide and other gases in the combustion emissions, absorb them and prevent them from escaping to the atmosphere. Monuments and StatuaryMarble is an attractive and easily worked rock that has long been used for monuments and sculpture. Its lack of significant porosity allows it to stand up well to freeze thaw action out-of-doors and its low hardness makes it an easy stone to work. It has been used in projects as large as the pyramids and as small as a figurine. It is widely used as cemetery markers, statues, mantles, benches, stairways and much more. Many Other UsesIn a powdered form, calcite often has an extremely white color. This quality makes it often used as a pigment or "whiting". Calcite has long been used as a whitewash and it is also used as one of the inert coloring ingredients of paint. Pulverized limestone or marble are often used as a dietary supplement in animal feed. Chickens that produce eggs and cattle that produce milk need to consume a calcium-rich diet. Small amounts of calcium carbonate are often added to their feeds to enhance their calcium intake. Calcite has a hardness of three on the Mohs scale and that makes it suitable as a low-hardness abrasive. It is softer than the stone, porcelain and plastic surfaces found in kitchens and bathrooms but more durable than food and other debris that people want to remove. Its low hardness makes it an effective cleaning agent that does not damage the surface being cleaned. Pulverized limestone is also used as a mine safety dust. This is a nonflammable dust that is sprayed onto the walls and roofs of underground coal mines to reduce the amount of coal dust in the air (which can be an explosion hazard). The mine safety dust adheres to the wall of the mine and immobilizes the coal dust. It's white color aids in illumination of the mine. Calcite: A Carbon Dioxide RepositoryCarbon dioxide is an important gas in Earth's environment. In the atmosphere it serves as a greenhouse gas that works to trap and hold heat near the surface of the planet. The processes of limestone formation remove carbon dioxide from the atmosphere and store it away for long periods of time. Enormous volumes of limestone and marble are hundreds of millions of years old. When these rocks are weathered, used to neutralize acids, heated to make cement or metamorphosed severely some of their carbon dioxide is returned to the atmosphere. |
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Transparent calcite from Baxter Springs, Kansas, showing characteristic cleavage. Specimen is approximately four inches (10 centimeters) across. 
Calcite in the form of oolitic limestone from Bedford, Indiana. Specimen is about four inches (ten centimeters) across.  Calcite in the form of chalk from Dover, England. Specimen is about 4 inches (10 centimeters) across. 
Calcite in the form of lithographic limestone from Solenhofn, Bavaria. Note the fine, uniform texture that is characteristic of lithographic limestone. Specimen is about 4 inches (ten centimeters) across. 
Calcite in the form of oolitic limestone from Tyrone, Pennsylvania. This specimen is approximately four inches (ten centimeters) across. 
Calcite in the form of translucent onyx from Tecali, Mexico. Specimen is about four inches (ten centimeters) across. 
Transparent calcite (known as "Iceland Spar") from Chihuahua, Mexico. This specimen shows excellent double refraction. Specimen is about four inches (ten millimeters) across . 
Calcite in the form of calcareous tufa from Mumford, New York. This specimen is approximately four inches (ten centimeters) across. 
Calcite in the form of travertine from Tivoli, Italy. Specimen is about four inches (ten centimeters) across. 
Calcite in the form of white, coarsely crystalline marble from Tate, Georgia. Specimen is about four inches (ten centimeters) across. 
Calcite in the form of a pink marble from Tate, Georgia. This specimen is approximately four inches (ten centimeters) across. 
Calcite in the form of siliceous crystals from Bad Lands, South Dakota. The calcite grew as crystals in a sand, including the sand grains within its crystal structure. Specimen is about five inches (twelve centimeters) across.
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