Rubidium is a very soft, silvery-white metallic element. Its atomic number is 37 and its symbol is Rb. Rubidium was discovered in 1861 by the German chemists, Robert Bunsen and Gustav Kirchhoff. It is the 16th most abundant element in the Earth’s crust (making rubidium a pretty common element). It belongs to a group of elements known as the alkali metals, such as sodium, potassium, cesium and lithium. Like the other alkali metals, rubidium reacts violently with air and water. When exposed to air, it bursts into flame. When put in water, it explodes. Its melting point is so low (103 degrees F, 40 degrees C) that it will melt on a very hot day. Scientists know that rubidium stimulates the metabolism. However, it is not known whether rubidium is beneficial to health. Rubidium does not combine with other elements or ions to create minerals. It is found, though, in trace amounts in the minerals that contain essential amounts of other alkali metals. These include the cesium and potassium rich zeolites, pollucite and leucite, and the lithium rich mica, zinnwaldite (a variety of the mineral lepidolite). One isotope of rubidium is radioactive. Because it is impossible to separate this isotope from non-radioactive rubidium, nearly all processed rubidium is slightly radioactive.

Rubidium is named from the Latin word rubidius which means dark red or deep red, in reference to the dark red spectroscopic lines.

According to the United States Geologic Survey (USGS) there is no accurate information about rubidium resources around the world. It is known that the United States imports 100% of the rubidium it consumes. It is believed that Canada is the most important supplier of rubidium ore to the U.S. A small number of American companies process rubidium ore (lepidolite).

Most rubidium is retrieved from the minerals lepidolite (a mica mineral) and pollucite. Both of these minerals are typical of a special igneous deposit known as a pegmatite. (A pegmatite is an igneous deposit where the magma (molten rock) cools so slowly that very, very large crystals form. Unusual and rare elements are typical in the minerals found in pegmatites.)

There are very few uses for rubidium. It is used in some medical and electronic applications. In general, rubidium is used mostly in laboratory studies. Rubidium may some day be used in space travel in what are called ion engines that can power spacecraft. It may some day be used to create very thin batteries.