Rb - Rubidium(L. rubidus, deepest red) Discovered in 1861 by Bunsen and Kirchoff in the minerallepidolite by use of the spectroscope. The element is much more abundant than was thought several years ago. It is nowconsidered to be the 16th most abundant element in the earth's crust. Rubidium occurs inpollucite, leucite, and zinnwaldite, which contains traces up to 1%, in the form of theoxide. It is found in lepidolite to the extent of about 1.5%, and is recoveredcommercially from this source. Potassium minerals, such as those found at Searles Lake,California, and potassium chloride recovered from the brines in Michigan also contain theelement and are commercial sources. It is also found along with cesium in the extensivedeposits of pollucite at Bernic Lake, Manitoba.