During magma crystallization, rubidium is concentrated together with its heavier analogue caesium in the liquid phase and crystallizes last.
Therefore, the largest deposits of rubidium and caesium are zone pegmatite ore bodies formed by this enrichment process.
Rubidium was discovered in 1861 by Robert Bunsen and Gustav Kirchhoff, in Heidelberg, Germany, in the mineral lepidolite through spectroscopy.
Because of the bright red lines in its emission spectrum, they chose a name derived from the Latin word rubidus, meaning "deep red". Both potassium and rubidium form insoluble salts with chloroplatinic acid, but those salts show a slight difference in solubility in hot water.
Although rubidium is more abundant in Earth's crust than caesium, the limited applications and the lack of a mineral rich in rubidium limits the production of rubidium compounds to 2 to 4 tonnes per year.Hence, the Rb/Sr ratio in residual magma may increase over time, and the progressing differentiation results in rocks with elevated Rb/Sr ratios.The highest ratios (10 or more) occur in pegmatites.Rubidium has also been reported to ignite spontaneously in air.Rubidium chloride (Rb Cl) is probably the most used rubidium compound: among several other chlorides, it is used to induce living cells to take up DNA; it is also used as a biomarker, because in nature, it is found only in small quantities in living organisms and when present, replaces potassium.Rubidium is a chemical element with symbol Rb and atomic number 37.Rubidium is a soft, silvery-white metallic element of the alkali metal group, with a standard atomic weight of 85.4678.Elemental rubidium is highly reactive, with properties similar to those of other alkali metals, including rapid oxidation in air.On Earth, natural rubidium comprises two isotopes: 72% is the stable isotope, Rb, with a half-life of 49 billion years—more than three times longer than the estimated age of the universe.However, rubidium ions have the same charge as potassium ions, and are actively taken up and treated by animal cells in similar ways.It is the second most electropositive of the non-radioactive alkali metals and melts at a temperature of 39.3 °C (102.7 °F).