Oval brilliant-cut pollucite, 9.51 cts, 16.3 x 12.7 mm, Afghanistan. © The Gem Trader. Used with permission.
Colorless pollucites lack fire when cut and are usually small. However, this very rare cesium mineral is a coveted collector’s gem.
| Data | Value |
|---|---|
| Name | Pollucite |
| Formula | Cs1-xNa,AlSi2O6· xh2O; x ~ 0.3. Also written: (Cs,Na)2(Al2Si4)O12 · H2O. |
| 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. |
| Colors | Colorless, white, gray; tinted pale pink, blue, violet. |
| Fracture | Conchoidal |
| Hardness | 6.5-7 |
| Cleavage | None |
| Crystallography | Isometric. Crystals cubic, very rare; massive, fine-grained. |
| Refractive Index | 1.518-1.525 |
| Birefringence | None |
| Dispersion | 0.012 |
| Luminescence | Blue-white and orange to pink fluorescence in UV and X-rays. Rarely pale yellow in SW UV. |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Long, UV-Short, X-ray Colors |
| Pleochroism | None |
| Optics | Isotropic; N = 1.518-1.525. |
| Luster | Vitreous, slightly greasy |
| Specific Gravity | 2.85-2.94 |
| Transparency | Opaque to transparent |
In this unusual mineral specimen, a pollucite crystal “brain” rests on an albite matrix with a thin, pinkish kunzite crystal at one end. Mawi, Laghman Province, Afghanistan. © Rob Lavinsky, www.iRocks.com. Used with permission.
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.
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.
Scientists have synthesized this mineral hydrothermally for use in the storage of radioactive waste. However, no commercial jewelry use for these synthetics is known.
No known gem treatments.
Notable gem-quality sources include the following:
Pollucite: Maine (gem ~ 2 cts). Photo © Joel E. Arem, PhD, FGA. Used with permission.
These pollucites on matrix show blue-white fluorescence. 14.0 x 11.0 x 8.5 cm (largest pollucite crystal measures 7 cm across). Shengus area, Skardu Road, Gilgit Division, Pakistan. © Rob Lavinsky, www.iRocks.com. Used with permission.
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.
Pollucites can reach the hardness of quartz (7) and require no special care or settings. Consult our gemstone jewelry care guide for more 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.
3.4-ct pollucite, 9 x 6 x 3 mm, Afghanistan. Photo courtesy of liveauctioneers.com and Jasper52.
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