What is Calcium Carbonate?

Calcium carbonate, or CaCO3, comprises more than 4% of the earth’s crust and is found throughout the world. Its most common natural forms are chalk, limestone, and marble, produced by the sedimentation of the shells of small fossilized snails, shellfish, and coral over millions of years. Although all three forms are identical in chemical terms, they differ in many other respects, including purity, whiteness, thickness and homogeneity. Calcium carbonate is one of the most useful and versatile materials known to man.

Many of us encounter calcium carbonate for the first time in the school classroom, where we use blackboard chalk. Chalk has been used as a writing tool for over 10,000 years and is a fine, microcrystalline material. As limestone, calcium carbonate is a biogenic rock, and is more compacted than chalk. As marble, calcium carbonate is a coarse-crystalline, metamorphic rock, which is formed when chalk or limestone is recrystallised under conditions of high temperature and pressure. Large deposits of marble are found in North America and in Europe; e.g., in Carrara, Italy, the home of the pure white “statuario” from which Michelangelo created his sculptures.