Rubidium is a chemical element with the symbol Rb and atomic number 37. It is part of group 1 of the periodic table and shares some similar properties with other alkali metals like sodium, potassium, and cesium. Rubidium is a soft, silvery-white metal that is highly reactive and easily oxidized. It has a relatively low melting point and boiling point, and can catch fire spontaneously when exposed to air or water. Rubidium is not found in its pure form in nature, but can be found in trace amounts in minerals like lepidolite, pollucite, and carnallite.

Rubidium has a number of applications in various fields. In the electronics industry, for example, it can be used to make highly sensitive sensors or in superconductive devices. It can also be used in the treatment of certain diseases like depression or in nuclear medicine imaging. It has also been used in experiments studying the behavior of matter at extremely low temperatures.