Monohydrocalcite is a mineral that is white when pure it forms a Mg-rich ACC that transforms using dissolution and reprecipitation.
It is a trigonal mineral which is white when pure. Monohydrocalcite forms via a Mg-rich amorphous calcium carbonate (ACC) precursor. This Mg-rich ACC forms rapidly (seconds) and then transforms to monohydrocalcite via dissolution and reprecipitation, with monohydrocalcite forming via a nucleation-controlled reaction like spherulitic growth. 
