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Home » Minerals » Calcite

Calcite


The unique properties of calcite make it suitable for a variety of uses


What is Calcite?



Calcite is a rock-forming mineral with a chemical formula of CaCO3. It is extremely common and found throughout the world in sedimentary, metamorphic and igneous rocks. Some geologists consider it to be a "ubiquitous mineral" - one that is found everywhere.

Calcite is the principal constituent of limestone and marble. These rocks are extremely common and make up a significant portion of Earth's crust. They serve as one of the largest carbon repositories on our planet.

The properties of calcite make it one of the most widely used minerals. It is used as a construction material, abrasive, agricultural soil treatment, construction aggregate, pigment, pharmaceutical and more. It has more uses than almost any other mineral.

The "Acid Test" for Carbonate Minerals


Calcite as Limestone and Marble



Limestone 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 also forms 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. A close examination of a broken piece of marble will usually reveal obvious cleavage faces of calcite. The size of the calcite crystals is determined by the level of metamorphism. Marble that has been subjected to higher levels of metamorphism will generally have larger calcite crystals.


Uses of Calcite in Construction



The 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 an important material used in prestige architecture.

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.


Physical Properties of Calcite

Chemical Classification carbonate
Color usually white but also colorless, gray, red, green, blue, yellow, brown, orange
Streak white
Luster vitreous
Diaphaneity transparent to translucent
Cleavage perfect, rhombohedral, three directions
Mohs Hardness 3
Specific Gravity 2.7
Diagnostic Properties rhombohedral cleavage, powdered form effervesces weakly in dilute HCl, curved crystal faces and frequent twinning
Chemical Composition CaCO3
Crystal System hexagonal
Uses


Uses in Acid Neutralization



Calcite 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 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 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 Sorbents



Sorbents 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. Calcium carbonate reacts with sulfur dioxide and other gases in the combustion emissions, absorbs them and prevents them from escaping to the atmosphere.


Monuments and Statuary



Marble is an attractive and easily worked rock that has long been used for monuments and sculptures. 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 Uses



In a powdered form, calcite often has an extremely white color. Powdered calcite is often used as a white pigment or "whiting". Some of the earliest paints were made with calcite. It is a primary ingredient in whitewash and it is used as an inert coloring ingredient of paint.

Pulverized limestone and 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 dried 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. Its white color aids in illumination of the mine. It is the perfect material for this use.


Calcite: A Carbon Dioxide Repository



Carbon 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 process of limestone formation removes carbon dioxide from the atmosphere and stores it away for long periods of time. This process has been occurring for millions of years - producing enormous volumes of stored carbon dioxide. When these rocks are weathered, used to neutralize acids, heated to make cement or metamorphosed severely some of their carbon dioxide is released and returned to the atmosphere. All of these processes of limestone formation and destruction have an impact on Earth's climate.


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double refraction in calcite
Transparent calcite (known as "Iceland Spar") from Chihuahua, Mexico. This specimen shows excellent double refraction. Specimen is about four inches (ten centimeters) across .


calcite as calcareous tufa
Calcite in the form of calcareous tufa from Mumford, New York. This specimen is approximately four inches (ten centimeters) across.


calcite as travertine
Calcite in the form of travertine from Tivoli, Italy. Specimen is about four inches (ten centimeters) across.


white calcite as marble
Calcite in the form of white, coarsely crystalline marble from Tate, Georgia. Specimen is about four inches (ten centimeters) across.


calcite sand crystals
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.


marble known as Picasso Stone
A variety of marble with brown and black markings is known as "Picasso Stone". It is frequently cut at polished as cabochons or used to produce tumbled stones. It is popular for jewelry and ornamental crafts.
   
calcite marble in the supreme court building
Calcite in the form of white marble was the primary stone used in the Supreme Court building. © iStockphoto and Gary Blakeley.




calcite as pink marble
Calcite in the form of a pink marble from Tate, Georgia. This specimen is approximately four inches (ten centimeters) across. See below for more calcite photos.


calcite in concrete used in a high rise building
Calcite in the form of limestone is used to make cement and also used as the aggregate in most concrete. A concrete slurry can be pumped or hoisted from the ground and poured into forms to produce the structural elements of buildings. © iStockphoto / Frank Leung


calcite as agrilime
Acid neutralizing qualities of calcite make finely crushed limestone a preferred material for soil treatment. © iStockphoto / Krzch-34


calcite as an antacid
The acid neutralizing ability of calcite is used in medicine. High-purity calcite was used to make these antacid tablets. © iStockphoto / Rudi Tapper


calcite as marble blocks
White marble blocks for monuments or statuary waiting transport from a quarry in Portugal. © iStockphoto / Manuel Ribeiro


calcite as travertine cave formations
Calcite cave formations of Luray Caverns, Virginia, USA. © iStockphoto / Daniel Yost


calcite with cleavage
Transparent calcite from Baxter Springs, Kansas, showing characteristic cleavage. Specimen is approximately four inches (10 centimeters) across.


calcite as oolite
Calcite in the form of oolitic limestone from Bedford, Indiana. Specimen is about four inches (ten centimeters) across.


calcite as chalk
Calcite in the form of chalk from Dover, England. Specimen is about 4 inches (10 centimeters) across.


calcite as lithographic limestone
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 as oolitic limestone
Calcite in the form of oolitic limestone from Tyrone, Pennsylvania. This specimen is approximately four inches (ten centimeters) across.


calcite as translucent onyx
Calcite in the form of translucent onyx from Tecali, Mexico. Specimen is about four inches (ten centimeters) across.


Mineral Information
 Anhydrite
 Apatite
 Arsenopyrite
 Augite
 Azurite

 Barite
 Bauxite
 Beryl
 Biotite
 Bornite

 Calcite
 Cassiterite
 Chalcocite
 Chalcopyrite
 Chlorite
 Chromite
 Chrysoberyl
 Cinnabar
 Clinozoisite
 Copper
 Cordierite
 Corundum
 Cuprite
 Diamond
 Diopside
 Dolomite

 Enstatite
 Epidote

 Fluorite

 Galena
 Garnet
 Glauconite
 Gold
 Graphite
 Gypsum

 Halite
 Hematite
 Hornblende

 Ilmenite

 Jadeite

 Kyanite
 Limonite

 Magnesite
 Magnetite
 Malachite
 Marcasite
 Molybdenite
 Monazite
 Muscovite

 Nepheline
 Nephrite

 Olivine
 Orthoclase

 Plagioclase
 Prehnite
 Pyrite
 Pyrophyllite
 Pyrrhotite

 Quartz

 Rhodochrosite
 Rhodonite
 Rutile
 Scapolite
 Serpentine
 Siderite
 Sillimanite
 Silver
 Sodalite
 Sphalerite
 Spinel
 Spodumene
 Staurolite
 Sulfur
 Sylvite

 Talc
 Titanite
 Topaz
 Tourmaline
 Turquoise

 Uraninite

 Witherite
 Wollastonite

 Zircon
 Zoisite


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