Calcium carbonate (CaCO₃) is a naturally occurring compound composed of calcium, carbon, and oxygen. It is one of the most abundant substances on Earth, found in rocks like limestone, marble, and chalk. It also occurs in biological materials such as shells, coral, and the bones and teeth of many animals. This white, odorless powder has a variety of physical and chemical properties that make it incredibly useful across multiple industries.

Chemically, calcium carbonate is a basic compound that reacts with acids to produce carbon dioxide gas, water, and a corresponding calcium salt. This reaction is central to many of its applications. For example, in the classroom, it is often used in demonstrations of acid-base reactions. When exposed to hydrochloric acid (HCl), it effervesces—producing bubbles of CO₂ gas.

One of the primary industrial uses of calcium carbonate is in construction. Ground limestone is a key ingredient in cement and concrete. Crushed marble and chalk are also used as building and decorative materials. Its durability, affordability, and availability make it ideal for large-scale construction projects.

In the paper industry, calcium carbonate is used as a filler to improve brightness and smoothness. Similarly, in plastics and paints, it serves as a white pigment and filler to enhance the quality and reduce production costs. In agriculture, it is used as a soil conditioner and pH regulator to neutralize acidic soils, improving crop yields.

Calcium carbonate also plays a significant role in human health. It is a common dietary supplement for calcium, essential for maintaining strong bones and teeth. Many over-the-counter antacids contain calcium carbonate, as it helps neutralize stomach acid and relieve symptoms of heartburn and indigestion.