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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.For several years in the 1950s and 1960s, a by-product of potassium production called Alkarb was a main source for rubidium.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.
Hence, the Rb/Sr ratio in residual magma may increase over time, and the progressing differentiation results in rocks with elevated Rb/Sr ratios.
Rubidium metal shares similarities to potassium metal and caesium metal in physical appearance, softness and conductivity.
Rubidium is the first alkali metal in the group to have a density higher than water, so it sinks, unlike the metals above it in the group. On Earth, natural rubidium comprises two isotopes: 72% is a stable isotope Rb, with a half-life of 49 billion years—more than three times longer than the estimated age of the universe.
They tried to generate elemental rubidium by electrolysis of molten rubidium chloride, but instead of a metal, they obtained a blue homogeneous substance, which "neither under the naked eye nor under the microscope showed the slightest trace of metallic substance".
They presumed that it was a subchloride ( In a second attempt to produce metallic rubidium, Bunsen was able to reduce rubidium by heating charred rubidium tartrate.