Atomic Number: 20
Relative Atomic Mass: 40.078
Category: Alkaline earth metal
Appearance: Silvery white metal
Above: Image © istockphoto.com/3dalia
Calcium, in its pure or elemental form, readily reacts with air and water. As a result, it cannot be found in nature. In fact, it wasn't until 1808 that elemental calcium was isolated by Cornish chemist Humphry Davy, when he carried out an electrolysis reaction on a mixture of lime (CaO) and mercury oxide (HgO).
However, calcium compounds are abundant, not to mention often very pretty and extremely useful. In fact, calcium is the fifth most common element in Earth’s crust (by weight). Commonly found calcium compounds include limestone (calcium carbonate, or CaCO3) and gypsum (calcium sulfate, or CaSO4). Furthermore, calcium is a key building block of life that is essential to bone health.
Construction and other industries
|South Foreland Lighthouse in Dover, Kent, England. The White Cliffs of Dover contain large amounts of limestone (Calcium carbonate) (Wikimedia Commons/Remi Jouan). Click image to enlarge
Did you know? Calcium salts are used in fireworks to produce a deep orange color.The iconic White Cliffs of Dover are made of limestone, which has been used as a construction material for over 4000 years. Famous structures built using limestone blocks include the Great Pyramid of Giza, the Colosseum of Rome, and the Empire State Building of New York.
Limestone has been used to create mortar and plaster for centuries. Slaked lime (calcium hydroxide) is a key ingredient of cement and is also used to reduce acidity in soil and water. In the chemical and mining industries, calcium is used to prepare various metals, including thorium and uranium, as well as aluminum, copper, and lead alloys.
The human body
Did you know? Calcium is the seventh most common element in the human body.There is about 1 kg of calcium in the average person. Calcium phosphate (CaPO4) is main material in bones and teeth, which contain about 99% of calcium in your body. The remaining 1% is essential to various important bodily functions, such as muscle contraction, nerve transmission, and hormone secretion. Calcium deficiency can cause long-term health problems, especially weaker bones.
You get the calcium your body needs from a variety of sources, including dairy products (milk, cheese, yogurt, etc.), almonds, vegetables (kale spinach, tomatoes, etc.), and tofu. Calcium is particularly important for children and teens, because their bones are growing rapidly. The recommended daily calcium intake for ages 9-18 is equivalent to about 4 glasses of milk, while most adults should consume the equivalent of about 3.5 glasses of milk.
Animal life and natural beauty
|Giant gypsum crystals in the Cave of the Crystals, Naica, Chihuahua, Mexico. Click image to enlarge (Paul Williams)
Did you know? Burning lime (calcium oxide, or CaO) in a mixture of oxygen and hydrogen produces intense light. Known as limelight, this method was commonly used in the 19th century for stage lighting in theatres.Human or, for that matter, other vertebrates are not the only animals that require calcium. For example, calcium carbonate is also the main component in the shells of mollusks.
Meanwhile, gypsum forms some of the largest crystals in the world. Gypsum crystals found in a cave in Chihuahua, Mexico, are so big you can actually walk on them! Calcium carbonate also forms stone icicles and pillars, called stalactites and stalagmites, in caves.
Can you find any other ways that calcium is used by humans or helps shape the natural world?
Periodic Table: Calcium (2014)
Royal Society of Chemistry
Variety of basic information on calcium with links to additional resources.
Calcium Facts (2014)
Short list of interesting facts about calcium.
Calcium: Dietary Supplement Fact Sheet (2013)
US National Institutes of Health
Comprehensive dietary information on calcium with extensive references.