Experimental Study of the Equilibrium Between Pollucite, Albite and Hydrothermal Fluid in Pegmatitic Systems

Ansom Sebastian and Martine Lagache
Laboratoire de Géologie, Ecole Normale Supérieure, URA 1316, rue Lhomond, 75005 Paris, France

Abstract: Pollucite is a silicate mineral of the rare element caesium, occurring in granitic pegmatites. Experiments have been carried out at 450, 600, and 750°C, 1.5 kbar, to study the equilibrium between pollucite, albite and the co-existing hydrothermal solution. When pollucite co-exists with albite, the alkaline composition of the solution is buffered. The Cs/Na ratio of the solution has been determined to be 0.11 at 450°C 0.22 at 600°C and 0.23 at 750°C. Pollucite contains about 15 mol.% of sodium, whereas albite is almost purely sodic. In nature, pollucite with more than 82 mol.% caesium has never been found. This can be explained by the absence of solutions in granitic pegmatites having a higher Cs/Na ratio than those determined by us.

Keywords: pollucite • albite • hydrothermal fluid • pegmatite • caesium

Mineralogical Magazine; September 1990 v. 54; no. 376; p. 447-454; DOI: 10.1180/minmag.1990.054.376.10
© 1990, The Mineralogical Society
Mineralogical Society (www.minersoc.org)