This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
This metal has not been found native. It occurs in the mineral kingdom as an oxide, chloride, silicate, or fluoride with potassium and aluminium (the lepidolite or rose mica of Bohemia). Bunsen and Matthiessen isolated it by means of electricity (1855).
Supposed at one time to be found in minerals only, it was named Aiflios, stony, but it is now recognized not only in many mineral waters, but in seas and rivers, vines and many fruits, the ashes of plants, and in most of our vegetable food (Bence Jones).
It is soft, silvery-white, and easily oxidizes: it floats upon water, and is the lightest known metal, the sp. gr. being 0.593G.