Rubidium is a relatively common element with an estimated concentration of about 90 parts per million, ranking about 16th in the Earth's crust in abundance. It is found as a minor component in many different minerals and not in its pure form, although it is more prevalent than elements like copper. The main objective of lepidolite extraction is to produce lithium, with most rubidium being a byproduct of this process. Typically, pure rubidium is obtained by reducing rubidium chloride using metallic calcium at low pressure and around 750°C.
With an atomic number of 37 and an average atomic mass of 85.47 g/mol, rubidium (Rb) is a member of the alkali metal group. Found by Kirchhoff and Bunsen in 1860, natural rubidium is a mixture of two isotopes: radioactive Rubidium-87 (27.85%) and Rubidium-85 (72.15%), making up around 0.01% of the Earth's crust.
Rubidium is a silvery-white, extremely soft metal and one of the most reactive elements on the periodic table. Its density is approximately 1.5 times that of water. Rubidium is solid at room temperature, though it melts with only a slight increase in temperature.
(Session 2025 - 26)