The hydrothermal synthesis of low albite

Glasses on the join NaAlSi₃O₈-Na₂Si₂O₅ were devitrified hydrothermally at pressures of 1 to 10 kb and at temperatures in the range 200 to 700° C to define more adequately the physical and chemical environments which favor crystallization of the fully ordered polymorph of albite. The presence of Na₂Si₂O₅ allows the synthesis of low albite with an obliquity of 1.140° (Cu K radiation) in runs of relatively short duration. The effect of increasing total pressure and time, and of decreasing temperature and amount of water down to critical values, is to favor the synthesis of ordered albite. Excess sodium is the chemical constituent necessary for ordering to proceed at a relatively rapid rate; this rate seems to vary with the ratio aNa⁺/aH⁺, and hence with the peralkalinity of the aqueous fluid attending recrystallization. The chemical environment of recrystallization thus seems as important as temperature in determining the ultimate degree of Si-Al order attained in albite.This paper is taken from a Ph. D. dissertation submitted to the Department of Geology, Stanford University, Stanford, California.