Alkaline Earth Metals
Calcium (Ca) is atomic number 20, has an atomic weight of 40.08 amu, and has melting and boiling points of 1,547.6 ±3°F (842 ±2°C) and 2,703.2°F (1,484°C), respectively. Davy isolated it in 1808 by electrolytic methods. It is the third most common metal on Earth, exceeded only by iron and aluminum, and the fifth most common element (41,000 parts per million in the earth's crust, and about 400 parts per million in seawater). The principle sources of calcium are limestone and dolomite (both carbonates), and gypsum (the sulfate). Other natural materials made of calcium carbonate include coral, chalk, and marble.
Calcium is an essential nutrient for living things, and its compounds find use in myriad industries. Both limestone and gypsum have been used in building materials since ancient times; in general, gypsum was used in drier climates. Marble is also a good building material. Limestone and dolomite are the principle sources of slaked lime (calcium hydroxide) and quick lime (calcium oxide) for the steel, glass, paper, dairy, and metallurgical industries. Lime can act as a flux to remove impurities from steel, as a neutralizing agent for acidic industrial waste, as a reagent for reclaiming sodium hydroxide from paper pulping waste, and as a "scrubbing" compound to remove pollutants from smokestack effluent. The paper industry uses calcium carbonate as an additive to give smoothness and opacity to the finished paper, and the food, cosmetic, and pharmaceutical industries use it in antacids, toothpaste, chewing gum, and vitamins.