Malic acid with double carboxylic groups also shows a
significant influence on the crystal morphology. It influences
the crystal morphology even at very low concentrations,
producing crystals elongated along [001] direction
[12]. A much earlier study showed that small quantities of
sodium malate favored the formation of calcite even in the
presence of Mg2+ ion [13]. Meldrum and Hyde [14]
observed a wide range of calcite morphologies produced
in the presence of both Mg and organic additives, and a
transition from single block to aggregate occurred on
increasing the Mg concentration. These morphologies
share a feature frequently encountered in biomineralized
calcite: orientational ordering, with relative tilt between
neighbor crystallites, resulting in curved faces