Calcite is a very common mineral and is a main component in chalk, limestone, and marble. Calcite is usually white in color but it can be found in many colors. In the picutre above, you can see that calcite can be orange in color. There is also Blue Calcite and Honey Calcite. Calcite is a crystalline form of calcium carbonate.
Calcium Carbonate (Shown above) is used as a primary component in antacids which are used to reduce stomach acid.