Element Caesium, Cs, Alkali Metal

It was the first metal to be discovered by the aid of the spectroscope (R. Bunsen, Berlin Acad. Ber., 1860) although caesium salts had undoubtedly been examined before, but had been mistaken by C. F. Plattner for potassium salts, meanwhile it was consisting of hydrous caesium and aluminium silicate. Later F. Pisani revealed it on the analysis of pollux in 1864. Investigating alkali metals spectra Bunsen recognized the light of well-known alkaline metals and alkaline earth elements; after precipitating lime, strontium, magnesia, he (actually they, since Gustav Robert Kirchhof has his share in this credit) saw the lines of sodium, potassium, and lithium, and in addition, two remarkable blue lines, one very close together and to strontium delta-line, and another, very bright-blue line right in the lithium neighbourhood. Bunsen believed that he could state that there was a fourth metal in the alkali group besides potassium, sodium, and lithium. He (actually they, since Gustav Robert Kirchhof has his share in this credit) proposed to give this new metal the name caesium (spelled cesium in American English) from caesius (Latin). Pure caesium was isolated electrolytically in 1882.

Alkali Metal Caesium is a relatively rare element, present at a crustal abundance of about 2.6x10^-4%, almost as bromine, hafnium and uranium.

Caesium is a trace element - it may be found dispersed in many rocks with concentrations of thousandths of a percent; negligibly small amounts of this element have been found also in seawater. It is more abundant, tenths of a percent, in some potassium and lithium minerals, mostly in lepidolite. In difference with rubidium and other rare elements it forms its own minerals such as pollucite (pollux), avogadrite and rhodizite. The latter (M₂Ox2Al₂O₃x3B₂O₃, where M₂O stands for alkaline metals) is extremely rare. It may be related to lithium minerals, because it is richer with lithium than by caesium. Avogadrite (K,Cs)[BF₄] is rare too. Pollucite (Cs,Na)[AlSi₂O₆]xnH₂O contains the biggest amount of caesium; it contains 29.8-36.7 mass % Cs₂O. One of the world's most significant and rich sources of this metal is at Bernic Lake in south-eastern Manitoba, Canada. The deposits there are estimated to contain 70% of world's caesium. Pollucite is found also in Namibia and Zimbabwe, 9 thousand and 23 thousand tons respectively, in Kazakhstan, Mongolia and Italy (Elba Island). In Russia it is found on Kola Peninsula, Eastern Sayans and Trans-Baikal regions.

Caesium is permanently present in living organisms. Seaweed contains 0.01-0.1 µg per 1 g of dry matter, terrestrial plants - 0.05-0.2. Animals receive caesium with water and food. Arthopods organisms contain 0.067-0.503 µg/g of caesium, reptiles 0.04 and mammals 0.05. Muscles, the heart and liver are the main caesium producers in the organism. Blood contains 2.8 µg/L of caesium. Caesium is slightly toxic, its biological role is not clear.