The microscopic growth mechanism of gibbsite is examined via crystallization in the presence of alkali metal ions, The morphology is found to be hexagonal plates in the presence of sodium, but hexagonal prisms in the presence of potassium and caesium. The former morphology is very similar to the calculated equilibrium morphology which ignores the effect of the growth medium. Further calculations examining the possible lattice sites of the incorporated defects show that different positions are most stable for sodium and potassium/caesium, providing an explanation for the different morphology.