Rubidium

Rubidium is a soft, silvery-white alkali metal that reacts violently with water and can ignite in air. It melts at about 39 °C, only a little above normal body temperature. In nature, it is bound in minerals rather than found as free metal. Sources include lepidolite, a lithium-bearing mineral, and pollucite, a source of cesium. Rubidium is recovered as a by-product of processing these minerals, then separated from chemically similar elements such as potassium and cesium. Rubidium atoms provide a precise timing reference in atomic clocks used in telecommunications. Scientists also use lasers to cool rubidium atoms to extremely low temperatures, allowing them to study unusual states of matter.