The effect of a range of inorganic and organic crystal growth modifiers on the morphology of Ca3Al2(OH)(12) has been studied. It has been found that some additives show a strong preference for a single crystal face forming polyhedral crystals whilst others are less selective, producing crystals with a less well-defined morphology. In this way sulphite and dithionite preferentially interact with the {111} face producing octahedral crystals and nitrilotriacetic acid stabilises. the {110} face forming rhombic dodecahedral crystals. Phosphate, however, leads to the formation of small needle-like crystals and the organic acids, N(CH2CO2H)(2)(CH2PO3H2), N(CH2CO2H)(CH2PO3H2)(2), HN(CH2PO3H2)(2), and H3CN(CH2PO3H2)(2), produce near spherical crystals. (C) 2002 Elsevier Science B.V.. All rights reserved.