Calcite, also known by the name calcspar, is calcium carbonate (CaCO3) containaing
56% CaO and 44% CO2. It gets its name from “chalix”, the Greek word for lime. Calcite
which crystallizes in a trigonal form, has two polymorphs, namely, aragonite (orthorhombic)
and vaterite (hexagonal). Amongst these, calcite is the most stable mineral at most
temperatures and pressures and in most environments. Aragonite, although a common
mineral, changes to calcite at 4700 C and vaterite is extremely scarce and rarely seen.
Though chemically same, calcite is different from limestone inasmuch as the former is a
crystalline mineral and the latter is a rock. Calcite is a chemical or biochemical calcium
carbonate and is one of the most widely distributed minerals constituting about 4% of the
earth’s crust. It is a common constituent of sedimentary rocks, limestone in particular. It is
also the primary mineral in metamorphic marble. It also occurs as a vein mineral in deposits
from hot springs, and also occurs in caverns as stalactites and stalagmites. Calcite is often the
primary constituent of the shells and hard parts of marine organisms like foraminifera, red
algae, some sponges and oysters.
The important uses of calcite are:
1. Optical instruments
2. Glass
3. Ceramic glaze
4. Decoration and ornamentation
5. Synthetic marble
6. Water treatment
7. Adhesive