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 andmarble. 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.
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
Physical Properties of Calcite |
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| 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 | Acid neutralization, a low-hardness abrasive, soil conditioner, heated for the production of lime |
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.
