The Jefferson Lab indicates that rubidium is used for removing gases in vacuum tubes, making photocells, and making certain glasses. It may also find use in propelling spacecraft engines. The element is likely be used more often as it becomes better understood.
The Jefferson Lab states that rubidium was initially discovered in 1861 by Robert Bunsen and Gustav Kirchoff while they were examining samples of the mineral lepidolite using a spectroscope. Upon looking at a sample, the two noticed some peculiar red lines. Bunsen then isolated samples of rubidium metal. In modern times, rubidium is obtained via refining lithium. Out of the compounds that rubidium can form, none are commercially useful. Common rubidium compounds include rubidium chloride, rubidium monoxide and rubidium copper sulphate. A combination of rubidium, silver and iodine is potentially useful in film batteries due to its electrical properties.
Lenntech states that rubidium, part of the alkali metal group, is soft and appears as silvery-white and metallic. Rubidium can become liquid during hot days and is known to act violently with water and ice. It's probably the 16th most common element within the earth's crust. Rubidium is considered to be similar to potassium in that it's not considered threatening by any environments. It exists in the minerals pollucite, carnallite, zinnwaldite and leucite. Very little rubidium is produced annually since there are few practical uses for it, but it's still used for research purposes. Rubidium is considered to be moderately toxic when ingested.