Calcium carbonate is an important chemical compound made up of one atom of calcium bonded to one atom of carbon and three atoms of oxygen. Its molecular formula is CaCO3. Common names for this compound include limestone, calcite, aragonite, chalk, and marble, and while all contain the same substance, each has different processes underlying its formation. Calcium carbonate is used in cements and mortars, producing lime, in the steel industry, glass industry, and as an ornamental stone.
This compound usually looks like a white powder or stone. It will fizz and release carbon dioxide upon contact with a strong acid, such as hydrochloric acid. After the carbon dioxide is released, the remainder is calcium oxide (CaO), commonly called quicklime.
When calcium carbonate comes into contact with water saturated with carbon dioxide, it forms a soluble compound, calcium bicarbonate. Underground, this often leads to the formation of caves. The reaction is as follows:
CaCO3 + CO2 + H2O → Ca(HCO3)2
Calcium carbonate becomes marble when highly compressed and heated deep underneath the Earth’s surface. In caves, when dissolved by the above chemical mechanism, it creates magnificent speleothems: cave formations such as stalagmites, stalagmites, curtains, and dozens of others. There are many mineral formations characteristic of this compound, but one of the most common forms is the scalenohedron, or “Dogtooth Spar,” for its resemblance to the canine tooth of a dog.
In the form of calcite, this material has an interesting optical property: double refraction. This occurs when a ray of light enters the crystal and splits into distinct fast and slow beams. When an observer looks through the crystal, he or she sees two images of everything behind it.
Calcium carbonate possesses other unusual properties, such as fluorescence and triboluminescence. This means that, when combined with a small amount of manganese and put under a UV light, it glows bright red. Under some conditions, the glow even persists when the UV light is removed. Triboluminescence, the property of demonstrating light when pieces of crystal are struck against each other, is more difficult to demonstrate, but it has been noted.
By Michael Anissimov