Simplify the following text for a Grade 10 native English-speaking person.
Original: 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 .
Simplified: Rubidium chloride is the most common rubidium compound . Rubidium hydroxide and rubidium carbonate are also used commonly .