CRYSTAL HABIT AND GROWTH-CONDITIONS OF BRUSHITE, CAHPO42H2O

Brushite, a polar compound, has been grown from aqueous solutions at 25 and 40-degrees-C in a large interval of concentrations, pH and supersaturations. The great variety of morphologies (aggregates, twins, regular and irregular crystals) are described and related to the growth conditions. The polar habit of brushite appears only under definite conditions. Four types of twins have been found, one of them occurring only at 40-degrees-C. The experimental crystal habit is compared to the theoretical crystal habit derived from the structure by the periodic bond chain (PBC) method. The form {111}, which has a high frequency, shows morphological instability due to its S character. The role played by the wrong incorporation of HPO42- in the kinks in forming the [010] twins and the irregular crystals is pointed out. The growth mechanisms of the most important faces are also discussed.