The element Erbium is a 'rare earth metal' or lanthanoid; in its pure state, it is a soft and malleable silver-white metal. Its atomic number is 68; its atomic symbol is Er. It is a natural solid, having a melting point of 1529 degrees centigrade. It has a relative atomic mass of 167.259, an atomic radius of 175.7 picometers, and a density of 9.07 grams per cubic centimetre. Like other lanthanoid metals, Erbium does not occur naturally as a pure metal; it is usually found mixed into mineral conglomerates called monaxite sand ores, which are complicated mixtures of a variety of lanthanoids with phosphorus and oxygen. Pure Erbium must be chemically reduced from a metallic salt which is extracted from the mineral ores in a complex, difficult, and potentially dangerous process involving sulfuric and hydrochloric acid and sodium hydroxide. Lanthanoids are not quite as 'rare' as the term rare earth might suggest, but because they are difficult to seperate they have only become comercially available as pure metals due to recent advances in ion-exchange purification technology.
Erbium is one of 3 chemical elements - along with Terbium and Ytterbium - which were named after the town of Ytterby, Sweden. This confusing circumstance is due to the work of the Swedish chemist Carl Gustav Mosander. In 1843 Mosander first successfully seperated the mineral gadolinite, a particularly complex compound of rare earths discovered in a quarry near Ytterby, into three distinct substances; he decided to name them yttria, erbia, and terbia. Terbia (which came to be called erbia, and vice versa, due to the similarity of their names and properties) was later found to be an Erbium oxide. It was not until 1934 that pure Erbium was produced in the laboratory.
Erbium has a number of industrial uses, as it is fairly stable and does not oxidize in air as quickly as other lanthanoids. It is used in metallurgy for adding malleability and softness to the harder metal Vanadium. Its characteristic sharp light absorption spectra also make it valuable in a number of optical applications. Erbium oxide is used to add a distinctive pink colour to glass and porcelain glazes, and has become fairly common in pink-tinted sunglasses, costume jewellery, and photographic filters. Its unique infrared light absorption qualities make it particularly useful as a signal amplifying agent in the manufacture of fiber optics intended for communication purposes. Erbium is also used to make lasers intended for industrial applications or for cosmetic and dental surgery, and it is sometimes used to make control rods in nuclear power plants.