Pollucite


Pollucite		\|(Cs,Na_n)(H₂O)_n\| [AlSi₂O₆], where Cs + n = 1

Morphology:
	Commonly massive to fine-grained granular. Rare crystals up to 12 cm may have cube, dodecahedron, or trapezohedron forms.

Physical properties:
	Cleavage: very poor. Fracture: uneven to conchoidal. Hardness: 6.5 - 7. Density: 2.68 to 3.03 gm./cm³. Luster: vitreous, greasy to dull. Streak: white.
				Pollucite crystals from Shengus, Roundu District, Gilgit-Baltistan, Pakistan. Copyright © Jose Zendrera.
Optical properties:
	Colorless, white, gray, pink, pale blue or violet. Colorless in thin section. Isotropic or very weakly anisotropic, n 1.507 - 1.525

Crystallography:
	Unit cell: Isometric, a 13.69 Å, Z = 16, Space group Ia3d.



Name:
	Breithaupt (1846) applied the name pollux to a mineral coexisting with castor (a variety of petalite) in pegmatite dikes on Elba, Italy. The names for the two minerals are for the twins Castor and Pollux of Greek mythology. Pollux was later modified to pollucite by Dana (1868).

Crystal structure:
	The similarity of the structure pollucite and analcime was noted by Strunz (1936), who suggested that the two minerals had the same space group, Ia3d, and the similar cell dimensions and cell contents. The tetrahedral framework of this group of microporous materials [ANA topology (Baerlocher et al. 2001),] contains 4- and 6-membered rings of tetrahedra that are considered as the secondary building units (SBU) as well as highly distorted (cradle-shaped) 8-membered rings that provide an irregular channel system within the framework (with approximate free cross-section ~4.2 × 1.6 Å). The topological symmetry of the framework type is cubic, with Ia-3d space group.
	Náray-Szabó (1938) made an attempt to refine the structure, basing it on the analcime structure, but placed the Cs ions in the Na cation sites of analcime. However, Beger (1969) solved the structure using single crystal X-ray diffraction data and accounted for the partial solid solution with analcime in his crystals. The structure of pollucite has the framework arrangement of analcime. Because of their size, the Cs cations (red) cannot occupy the Na (yellow) sites of analcime, but instead are in the W (H₂O) sites. The Na and H₂O of the analcime component of most pollucite crystals occupy the usual Na and W sites of the analcime structure. Teertstra et al. (1994) studied the Si,Al disorder of cesian analcime and pollucite with magic-angle-spinning nuclear magnetic resonance spectroscopy. Their results show that isotropic pollucite is largely disordered, while anisotropic samples have a slight degree of ordering. Kamiya et al. (2008) reported that the space group C2/c, monoclinic, is found to be the most probable space group for this mineral based on the systematic absences of reflections by single-crystal X-ray diffractometry.
	Cesium ions or water molecules are disordered at the center of a channel and are slightly apart from the special position. This is the origin of symmetry breaking and the space group becomes lower from Ia-3d (analcime) to C2/c. Sodium ions or vacancies are located at the contact point of the channel. No ordering of aluminum is observed in the pollucite structure. A detailed description of the crystal structure and crystal chemistry of pollucite (e.g., Si/Al-distribution, configuration of the extra-framework content, possible hydrogen bonding scheme) was reported by Gatta et al. (2009a) who provided the key to understand the high thermo-elastic stability of pollucite (Gatta et al. 2009b), the immobility of Cs at non-ambient conditions, and the extremely low leaching rate of Cs. The dehydration experiments on natural pollucites showed no loss in weight below 573 K, with a completely dehydrated form at 913 K (Fleischer and Ksanda 1940). Transformation of natural pollucite into hexacelsian occurs under high pressure and temperature conditions (Choi et al. 2022).

Chemical composition:
	Analyses of pollucite published by Cerný (1974, 1982) and Teertstra and Cerný (1995) show that a complete series exists between analcime and pollucite. The analyses from these sources show compositions across the range (see the accompanying plot). The framework consists mostly of Si and Al, but small amounts of Fe and P have been detected in some samples. The generalized composition with Si/Al = 2, seldom occurs in natural crystals, but is approached in those nearest the pure Cs end member. Teertstra and Cerný (1995) note that sodian pollucite tends to have the highest Si contents (> 34 Si per unit cell, Si/Al near 2.42, and T_Si = 0.707), while the most Cs-rich crystals have lower Si contents (32.4 Si per unit cell, Si/Al < 2.1, and T_Si = .675). With modern instrumental analyses small amounts of several non-framework cations, other than Cs and Na, can be determined. Rb and K are commonly present, and Li, Ca, and Mg, in lesser amounts. The composition of pollucite samples are expressed in two slightly different ways. %CRK (Cs+Rb+K) represents the total cation occupancy in the W site, while %Poll is only the Cs content. CRK cations -- Na?site cations -- Si variations for some examples of pollucite from Teertstra and ?erný (1995) and Teertstra et al. (1992) are shown in the accompanying figure. Primary pollucite samples contain 70 to 80% CRK, while recrystallized pollucite compositions are somewhat more sodic or much more cesian, tending toward the pure pollucite end member (Teertstra and Cerný 1995). The cesian analcime samples are from veins of low temperature alteration products in spodumene of the Tanco pegmatite at Bernic Lake, Manitoba, Canada (Cerný 1972). A recent study shows that pollucite from Maine, USA contains CO 2 in the structural cavities (Bellatreccia et al. 2012)

Occurrences:
	Pollucite occurs only in complex, rare-element granitic pegmatite dikes as a product of extreme alkali-metal fractionation. It crystallizes as one of the latest primary mineral phases in the pegmatite and/or as a product of even later hydrothermal alteration of primary minerals. Pollucite has been interpreted as occurring mainly in two ways (Cerný 1982), primary crystallization and late metasomatic alteration. Dymkov (1953), Quensel (1956), Hutchinson (1959), Ginsburg (1960), Solodov (1960), and Wright (1963) argue for a late metasomatic origin. Textural evidence comes mainly from dikes with low pollucite content, in which granular, dispersed pollucite is associated with Ta, Nb, Sn, B. and P minerals of the typical albitization assemblages. Beus (1960), Melentyev (1961, 1970) Symons (1961), Cooper (1964), Crouse and Cerný (1972), Heinrich (1976), Cerný and Simpson (1978), Cerný (1982), Teertstra et al. (1992), and Teertstra and Cerný (1995) consider pollucite as a primary constituent of the near-central parts of pegmatite dikes. Evidence supporting this view comes from those dikes, in which pollucite forms large pods or lenses in well-defined bodies. Boundaries of these pods are simple, showing no evidence of cross-cutting or replacement with other minerals or zones of minerals. Cerný (1982) comments that the evidence for a metasomatic origin resembles the relationships seen in secondary crystallization and alteration in zones surrounding primary pods. Teertstra and Cerný (1995) estimate that primary pollucite crystallizes from a water-rich melt late in the solidification of the dike, probably in the temperature range 550 to 400°C. Based on minerals in fluid-solid inclusions from the Tanco pegmatite, London (1986) inferred the transition from magmatic to subsolidus hydrothermal conditions occurred between about 450° and 475°C. Where primary pollucite crystallizes in the presence of quartz, the composition is buffered by quartz and albite giving a composition near %Poll = 80.
			Primary pollucite is invariably altered by late stage fluids, causing several kinds of alteration. This alteration has been studied by Cerný and Simpson (1978), Teertstra et al. (1992), Teertstra et al. (1993), and Teertstra and Cerný (1995). The generalized scheme of this alteration (Teertstra and Cerný 1995) is shown in the accompanying figure from Deer et al. (2004). The left side of the diagram illustrates open system alteration with various constituents introduced into fractures or in replacement veins, cutting pollucite and resulting in crystallization of quartz, potassium feldspar, albite, muscovite, and spodumene. Alteration processes on the right side of the diagram, at least initially, are interpreted as almost closed system effects. Exsolution-like textures are illustrated by Teertstra et al. (1992), Teertstra et al. (1993), and Teertstra and Cerný (1995), but Lagache (1995) argues that a subsolidus solvus is not proven by experimental work. Some veinlets, cutting primary pollucite, contain Cs-rich pollucite and quartz. See illustrations in Teertstra et al. (1992) and Teertstra and Cerný (1995). These veinlets are bordered by pollucite depleted in the Cs,Al component. According to this same model, alteration of pollucite continues as long as fluids are circulating in the fractures of the dike.

References:
	Beger, R.M. (1969) The crystal structure and chemical composition of pollucite. Z. Kristallogr. 129, 280-302. Bellatreccia, F., Ventura, G. Della, Gatta, G. D., Guidi, M. Cestelli and Harley, S. (2012) Carbon dioxide in pollucite, a feldspathoid with the ideal composition (Cs,Na)₁₆Al₁₆Si₃₂O₉₆·nH₂O. Mineral. Mag., 76 (4) 903-911. Beus, A.A. (1960) Geochemistry of beryllium and the genetic types Freeman and Co., 1966). Breithaupt, A. (1846) Pollux. (Poggendorff’s) Annalen der Physik und Chemie 69, 439. Cerný, P. (1972) The Tanco pegmatite at Bernic Lake, Manitoba. VIII. Secondary minerals from the spodumene-rich zones. Can. Miner. 11, 714-726. Cerný, P. (1974) The present status of the analcime-pollucite series. Can. Mineral. 12, 334-341. Cerný, P. (1982) Mineralogy of rubidium and cesium. In, Cerný, P. (ed.) Short Course in Granite Pegmatites in Science and Industry, Min. Assoc. Canada, Handbook 8, 149-161. Cerný, P. and Simpson, F.M. (1978) The Tanco pegmatite at Bernic Lake, Manitoba. X. Pollucite. Can. Mineral. 16, 325-333. Choi, W., Choi, J., Hwang, H. and Lee, Y. (2022) Transformation of natural pollucite into hexacelsian under high pressure and temperature. Phys. Chem. Miner., 49(5), p.15. Cooper, D.G. (1964) The geology of the Bikita pegmatites. In, The Geology of Some Ore Deposits in Southern Africa II, 441-462. Crouse, R.A. and Cerný, P. (1972) The Tanco pegmatite at Bernic Lake, Manitoba. I. Geology and paragenesis. Can. Mineral. 11, 591-608. Dana, J.D. (1868) A System of Mineralogy (5th ed.) John Wiley and Sons, New York, N.Y. Deer, A., Howie, R., Wise, W.S., and Zussman, J. (2004). Rock Forming Minerals. vol. 4B. Framework Silicates: Silica Minerals, Feldspathoids and the Zeolites. The Geological Society, London. Dymkov, Yu. M. (1953) Morphology of pollucite aggregates and their genesis. Trudy Mineral. Mus. Akad. Nauk SSSR 5, 132-145. Fleischer, M. and Ksanda, C.J. (1940) Dehydration of pollucite. Am. Mineral., 25, 666–672. Gatta, G. D., Rinaldi, R., McIntyre, G. J., Nénert, G., Bellatreccia, F., Guastoni, A., & Ventura, G. D. (2009a). On the crystal structure and crystal chemistry of pollucite,(Cs, Na)₁₆ Al₁₆Si₃₂O₉₆· n H₂O: a natural microporous material of interest in nuclear technology. Am. Mineral., 94(11-12), 1560-1568. Gatta, G.D., Rotiroti, N., Boffa Ballaran, T., Sanchez-Valle, C. and Pavese, A., (2009b) Elastic behavior and phase stability of pollucite, a potential host for nuclear waste. Am. Mineral., 94(8-9), 1137-1143. Ginsburg, A.I. (1960) Specific geochemical features of the pegmatitic process. Rept. 21st Int. Geol. Congr. 17, 111-121. Heinrich, E.W. (1976) A comparison of three major lithium pegmatites: Varuträsk, Bikita, and Bernic Lake. U.S.Geol.Surv., Prof. Paper 1005, 50-54. Hutchinson, R.W. (1959) Geology of the Montgary pegmatite. Econ. Geol. 54, 1525-1542. Kamiya, N., Nishi, K., ∧ Yokomori, Y. (2008). Crystal structure of pollucite. Zeit. Kristall., 223(9), 584-590. Lagache, M. (1995) New experimental data on the stability of the pollucite-analcime series: application to natural assemblages. Eur. J. Mineral. 7, 319-323. London, D. (1986) The magmatic--hydrothermal transition in the Tanco rare-element pegmatite: evidence from fluid inclusions and phase equilibrium experiments. Am. Mineral. 71, 376-395. Melentyev, G.B. (1961) New find of pollucite in the granitic pegmatites of Sayan Mts. Dokl. Akad. Nauk SSSR 141, 950-953. Melentyev, G.B. (1970) First find of pollucite-bearing pegmatites in Central Asia and new data on the conditions of cesium accumulation. Dokl. Akad. Nauk SSSR 192, 180-183. Náray-Szabó, St. V. (1938) Die Struktur des Pollucits CsAlSi2O6.xH2O. Z. Kristallogr. 99, 277-282. Quensel, P. (1956) The paragenesis of the Varuträsk pegmatite. Ark. Mineral. Geol. 2, 9-125. Solodov, N.A. (1960) Distribution of alkali elements and beryllium in minerals of one of the zoned pegmatites of the Mongolian Altai. Geokhimiya 1960, 726-735. Strunz, H. (1936) Die chemische Zusammensetzung von Pollucit. Z. Kristallogr. 95, 1-. Symons, R. (1961) Operation at Bikita Minerals (Private), Ltd., Southern Rhodesia. Bull. Inst. Mining and Metall. 661, 129-172. Treetstra, D.K., Lahti, S.I., Alviola, R. and Cerný, P. (1992) Compositional heterogeneity of pollucite from High Grade Dyke; Maskwa Lake, southeastern Manitoba. Can. Mineral. 30, 687-697. Treetstra, D.K., Lahti, S.I., Alviola, R. and Cerný, P. (1993) Pollucite and its alteration in Finnish pegmatites. Geol. Soc. Finland, Bull. 368, 39 pp. Treetstra, D.K., Sherriff, B.L., Zhi Xu, and Cerný, P. (1994) MAS and DOR NMR study of Al-Si order in the analcime-pollucite series. Can. Miner. 32, 69-80. Treetstra, D.K. and Cerný, P. (1995) First natural occurrences of end-member pollucite: a product of low-temperature reequilibrium. Eur. J. Mineral. 7, 1137-1148. Wright, G.M. (1963) Geology and origin of the pollucite-bearing Montgary pegmatite, Manitoba. Geol. Soc. Am. Bull. 74, 919-946. Updated: November 2025.