Calcium carbonate exists in various forms, each with distinct properties. Calcite is the most common crystalline form, found in limestone and marble. Aragonite is another crystalline variety, occurring in mollusk shells and coral reefs. Vaterite, a less stable polymorph, is found in some geological formations and precipitation experiments. Precipitated calcium carbonate (PCC) is a finely ground, synthetic form produced for diverse applications. Chalk, a soft variety, is composed of microcrystalline calcium carbonate. Additionally, calcified structures like stalactites and stalagmites in caves, and the mineral travertine, formed in hot springs, are examples of calcium carbonate in different geological settings.