Chalk is composed mainly of calcium carbonate (CaCO3), which is a naturally occurring mineral called calcite. Calcite is formed when calcium carbonate precipitates out of water, often as a result of the evaporation of seawater or other bodies of water rich in calcium carbonate. Over time, layers of calcite can accumulate and compress to form chalk. Chalk can be found in various locations around the world, including the famous chalk cliffs of Dover in the United Kingdom, as well as in parts of France, Denmark, and the United States.