Pollucite belongs to the zeolite mineral group. It forms a solid solution series, as the cesium (Cs) analogue, with analcime, the sodium analogue.
Not only is gem-quality pollucite very rare, it’s also the only mineral which has Cs as an essential constituent. This mineral serves as the principal ore for cesium.
You’re more likely to find this gem in mineral collections than in jewelry collections. However, recent gem-quality finds in Afghanistan could change that.
How Did Pollucite Get Its Name?
Discovered in 1846 in Elba, Italy, this mineral was named after Pollux, the twin brother of Castor in Classical mythology. (Helen of Troy and the ill-starred Clytemnestra were his sisters). The discoverers associated it with castorite, named after Castor, since both occurred in lithium-rich granite pegmatites at this source. Although castorite was later renamed petalite, the name pollucite remained.
Oddly enough, according to myth, Pollux was immortal while Castor was mortal. So, too, did the name “castorite” pass away. Furthermore, some myths claim the twins had different fathers, immortal Zeus and the mortal Tyndareus. So, though originally paired, these minerals proved to be distinct, too.
Notable gem-quality sources include the following:
United States: Gem material from various localities in Maine, including Newry and Mt. Mica, and Massachusetts; San Diego County, California; Middletown, Connecticut; Custer County, South Dakota: massive material in thick seams.
Note: In metal form, cesium is toxic, and the isotopes produced as nuclear waste or for medical purposes are radioactive. However, naturally occurring cesium, such as that found in pollucite gems, should pose no risks.