Rubidium is named from the Latin rubidius, deepest red and was discovered in 1861. Rubidium is the 16th most abundant element in the earth's crust and occurs in pollucite, carnalite, leucite and zinwaldite, which contains traces up to 1% in the form of the oxide. It is found in lepidolite to the extent of 1.5% and is recovered commercially from this source. Rubidium can be liquid at room temperature. It is a soft, silvery-white metallic element of the alkali group and is the second most electropositive and alkaline element. Rubidium has been used as a getter in vacuum tubes and as a photocell component. It has been used in making special glasses.