Calcium is a chemical element with the symbol Ca and atomic number 20. It is an alkaline earth METAL and one of the most abundant elements in the Earth's crust. QUICKLIME, also known as calcium oxide, is a white powdery substance made by heating limestone or other calcium-containing materials in a kiln. METAL is an alloy of two or more elements, at least one of which is a METAL. Calcium is often combined with other metals to form alloys such as brass and bronze. Limy is an adjective used to describe something that contains a lot of calcium, such as limestone or chalk. NITRATE is a salt or ester of nitric acid, containing the anion NO3-. Calcium NITRATE is a common fertilizer used to provide nitrogen to plants.