|Robert Bunsen and Gustav Kirchhoff, the creators of spectral analysis (1859), immediately applied it as an auxiliary method of chemical analysis and soon caesium was discovered. During their investigations they became interested in the mineral lepidolite (potassium lithium aluminium silicate hydroxide fluoride). The processed 150 kg and, as a result, separated double potassium, caesium and rubidium chloroplatinates from alkali metals containing fractions treating them by chloroplatinic acid H2PtCl6. Potassium salts were water-soluble than those of rubidium and caesium, helped them to isolate the former from the latter. In the residue spectrum new red lines were detected. Bunsen and Kirchhoff were right supposing that the new lines belong to a new element which they named Rubidium (Latin: rubidus, deepest red).|
|The crustal abundance of rubidium is 7.8x10-3%, almost as the one of nickel and copper. This element is considered to be the 16th most abundant element in the Earth's crust. It is a typical trace element. There are no known rubidium minerals. Rubidium is associated with alkali metals, especially with potassium. It is traced in many minerals deposited in North America, South Africa and Russia; however its concentrations are extremely low. Lepidolites contain more rubidium, approximately 0.2%, sometimes even up to 1-3% (taking Rb2O into account).|
Rubidium salts are dissolved in seawater with low concentrations, approx. 100 µg/l. In some areas it may have bigger concentrations; for instance in Odessa limans (Ukraine) it may reach up to 670 µg/l, and in the Caspian Sea up to 5700 µg/l. Rubidium highest concentrations are detected in Brazilian mineral water sources.
Rubidium transferred from seawater into potassium deposits, mostly into carnallites, very complex chemical compounds with formula KClxMgCl2x6H2O. Rubidium concentrations in them may vary from 0.037 till 0.15%.
Rubidium permanently occurs in living tissues: 0.00064% in terrestrial flora, and the half of it - in water plants. Rubidium is accumulated in muscles and soft tissues of actinia, worms, mollusks, crustaceans, echinoderms and fish, with the accumulation coefficient 8.26. Duckweed Lemna polyrrhiza has the biggest accumulation coefficient of 86Rb equal 2600, and in mollusk Galba palustris 370. Rubidium concentrations are 0.0112-0.0135% in birds' breast muscles ashes, 0.01%, 0.01% in human tissues ashes, 0.00032% and 0.00032% in human male and female blood respectively. Rubidium metabolism is studied slightly.