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Physical Properties
Color silvery-white
Phase at Room Temp. solid
Density (g/cm3) 1.532
Hardness (Mohs) 0.3
Melting Point (K) 312.09
Boiling Point (K) 961
Heat of Fusion (kJ/mol) 2.176
Heat of Vaporization (kJ/mol) 76
Heat of Atomization (kJ/mol) 86
Thermal Conductivity (J/m sec K) 58.2
Electrical Conductivity (1/mohm cm) 77.9
Source Li extractn by-product
Atomic Properties
Electron Configuration [Kr]5s1
Number of Isotopes 2
Electron Affinity (kJ/mol) 46.885
First Ionization Energy (kJ/mol) 403
Second Ionization Energy (kJ/mol) 2632.1
Third Ionization Energy (kJ/mol) 3859.4
Electronegativity 0.82
Polarizability (Å3) 47.3
Atomic Weight 85.4678
Atomic Volume (cm3/mol) 55.8
Ionic Radius2- (pm) ---
Ionic Radius1- (pm) ---
Atomic Radius (pm) 248
Ionic Radius1+ (pm) 166
Ionic Radius2+ (pm) ---
Ionic Radius3+ (pm) ---
Common Oxidation Numbers +1
Other Oxid. Numbers ---
In Earth's Crust (mg/kg) 9.0×101
In Earth's Ocean (mg/L) 1.2×10-1
In Human Body (%) 0.001 %
Regulatory / Health
CAS Number 7440-17-7
OSHA Permissible Exposure Limit (PEL) No limits
OSHA PEL Vacated 1989 No limits
NIOSH Recommended Exposure Limit (REL) No limits
University of Wisconsin General Chemistry
Mineral Information Institute
Jefferson Accelerator Laboratory

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.

Substitutes and Alternative Sources

The physical and chemical properties of cesium and cesium compounds are so similar to those of rubidium and rubidium compounds, that they can be used interchangeably.

Further Reading



Institute, M. (2008). Rubidium. Retrieved from


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