Colorless pollucites lack fire when cut and are usually small. However, this very rare cesium mineral is a coveted collector's gem.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Isometric. Crystals cubic, very rare; massive, fine-grained.|
|Colors||Colorless, white, gray; tinted pale pink, blue, violet.|
|Luster||Vitreous, slightly greasy.|
|Luminescence||Orange to pink ﬂuorescence in UV and X-rays. Rarely pale yellow in SW UV.|
|Transparency||Opaque to transparent.|
|Formula||Cs1-xNa,AlSi2O6· xh2O; x ~ 0.3. Also written: (Cs,Na)2(Al2Si4)O12 · H2O.|
|Optics||Isotropic; N: 1.518-1.525.|
|Etymology||Named after Pollux, the twin brother of Castor in Classical mythology.|
|Occurrence||In granite pegmatites.|
|Inclusions||Usually whitish, resembling spikes or balls, very small; also very tiny snowflakes, bulging at the centers.|
Not only is gem-quality pollucite very rare, it’s also the only mineral which has cesium (Cs) as an essential constituent. This mineral serves as the principal ore for cesium.
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.
No known gem treatments.
Notable gem-quality sources include:
- 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.
- Afghanistan; Bernie Lake, Manitoba, Canada; Finland; Elba, Italy; Kazakhstan; Pakistan; Karibib, Namibia; Varutrask, Sweden: massive lilac to white material (N = 1.518, SG 2.90).
Despite the existence of large beds at some localities, gems sizes are always very small, under 10 carats.
Opaque, whitish masses in South Dakota reach 3-4 feet in thickness but usually yield colorless, very small gems.
Maine material cuts stones from masses that reach up to 10 inches in size.
- Smithsonian Institution (Washington, D.C): 8.5 (colorless, Maine); 7.0 (colorless, Connecticut).
- Private Collection: 3.85 (pinkish, Maine).
Pollucites can reach the hardness of quartz (7) and require no special care or settings. 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. See the faceted gem below. Consult our Gemstone Jewelry Cleaning Guide for general care recommendations.
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.