An Etymological Dictionary of Astronomy and Astrophysics

A metallic → chemical element; symbol Li. → Atomic number 3; → atomic weight 6.941; → melting point about 180.54°C; → boiling point about 1,342°C. Lithium is a soft, silver-white metal. It is the lightest metal and one of the alkali metals in Group 1 of the → periodic table. Lithium does not occur on Earth in its free form. It is a minor part of almost all igneous rocks and is found in many natural brines, in total 0.0007% of the Earth’s crust. It has two stable → isotopes, ⁷Li (92.5%) and ⁶Li (7.5%). The element was discovered in the mineral petalite, LiAl(Si2O5)2, by the Swedish mineralogist Johan August Arfwedson in 1817. It was isolated by W.T. Brande and Sir Humphrey Davy. Many uses have been found for lithium and its compounds. Lithium has the highest → specific heat (3.6 J/gK) of any solid element and is used in heat transfer applications. It is used in rechargeable lithium ion batteries. It is also used as an alloy with → aluminum, → copper, and → manganese to make high performance aircraft parts. It is used to make special glasses and ceramics, including the Mount Palomar telescope’s 5 m mirror. Lithium also has various nuclear applications, for example as a coolant in nuclear breeder reactors and a source of → tritium, which is formed by bombarding lithium with neutrons. In medicine it is used to treat bipolar disorder (manic depression), a serious mental illness that causes extreme shifts in mood, energy, and functioning.

In astrophysics, → Spite plateau.

See also: Lithium, from L. lithos “stone” because lithium was thought to exist only in minerals.