Distribution of D2O Molecules of First and Second Types in Hydrothermally Grown Beryl Crystals

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This article reports on the uneven distribution of water molecules of first (D 2 O-I) and second (D 2 O-II) types in a D 2 O-containing beryl crystal grown hydrothermally on a non-singularly oriented flat seed {5.5.10̅.6}, as identified by infrared spectroscopic studies of crystal fragments. The distribution of D 2 O-II molecules is very heterogeneous, and their maximal concentrations are at the boundaries of the growth sectors of micro-faces, which protrude from the surface growth front {5.5.10̅.6}. We attribute this increase in the D 2 O-II content to the tensions and the resulting increased internal pressure at the boundaries of the growth sectors of micro-faces. Specifically, the increased internal pressure shifts the isomorphic substitution equation in beryl Si T 1 4+ → Al T 1 3+ + Li R″ + to the right (T 1 and R″ denote the crystal’s chemical positions of cations), which triggers the D 2 O-I → D 2 O-II transformation. The number of growth sector boundaries goes down as the growth front moves, reducing the number of areas with increased internal pressure and the proportion of D 2 O-II/D 2 O-I.

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