Rubidium hydroxide and rubidium carbonate are also used commonly . Other common rubidium compounds are the corrosive rubidium hydroxide ( RbOH ) , the starting material for most rubidium-based chemical processes ; rubidium carbonate ( RbCO3 ) , which is used in some optical glasses , and rubidium copper sulfate , Rb2SO4 â cents CuSO4 â cents 6H2O .