Crystallization of zoned (Ba, Pb)SO4 single crystals from aqueous solutions in silica gel

Zoned single crystals of the BaSO4–PbSO4 solid solution have been grown from aqueous solutions in a diffusing reacting system at high supersaturation levels. The crystals have been characterized by scanning electron microscopy, EDAX and electron microprobe. Under the experimental conditions used, nucleation and crystal growth was influenced by multiple kinetic and thermodynamic factors. The low solubility of barite (BaSO4) compared to anglesite (PbSO4) implies a strong preferential partitioning of barium to the solid phase, but the distribution of the substituting ions between the solid and aqueous phases is also influenced by supersaturation that tends to soften this preferential partitioning. The chemical evolution of the system during crystal growth implies a morphological and compositional evolution of the solids that is recorded as “internal morphologies,” which have been observed in central sections of the crystals.