EFFECTS OF CALCIUM-BINDING POLYSACCHARIDES FROM CALCAREOUS ALGAE ON CALCIUM-CARBONATE POLYMORPHS UNDER CONDITIONS OF DOUBLE DIFFUSION

The effects of calcium-binding acid polysaccharides from magnesian-cal cite-depositing algae, and a potent scale inhibitor, hydroxyethylidene 1,1-diphosphonic acid (HEDP), on CaCO3 Polymorphs were studied by a d ouble diffusion technique. Magnesian calcite was formed with aragonite by adding the acid polysaccharides or HEDP to the agar-gel even in th e presence of Mg2+ in Ca2+ solution (Ca2+ concentration, 0.1M; Ca2+/Mg 2+ = 2.0), and the ratio of magnesian calcite to aragonite increased w ith increasing amounts of the additives. These results suggest that ma gnesian calcite was formed by transformation of aragonite nuclei into calcite ones with the inhibition of aragonite growth by acid polysacch arides or HEDP. The effects of the acid polysaccharides explain the oc currence of magnesian calcite in these algae.