When Ca and CO₃ ions were mixed under highly supersaturated conditions in neutral to weak basic aqueous solution conditions which simulated biological environment, amorphous calcium carbonate (ACC) was appeared as an initial phase and rapidly transformed into vaterite. According to non-classical nucleation thesis, this phase transformation process is assumed as continuously structural reconstructions in cluster based phase transformation from amorphous phase to crystalline. Appearance of some intermediate phases during phase transformation in general. However, the phase transformation process has been little known, for examples, physicality, chemical composition and structure. Finely identify of the intermediate phase and measurement of their dynamics bring us new aspects for phase transformation of not only calcium carbonate but also other cluster based minerals like calcium phosphate.

      Vaterite was often formed as round-shaped spherulites particles in supersaturated calcium carbonate solutions in around neutral to weak based aqueous solutions. Sugiura et al.  showed vaterite spherulites become hollow structure during dissolution process in a solution including PO₄ ions. This result suggests that vaterite spherulites were consisted of two or more vaterite like and lower stability phases and they were ranging inside part of vaterite spherulites and these phases were assumed as intermediate phases between ACC to vaterite.

      We had done fine phase identification for inside phase of vaterite spherulites using powder X-ray structural analysis, selected area electron diffraction (SAED) analysis and measuring chemical composition, and estimated growth and dissolution rate of these intermediate phases in simulated biological temperature and pressure environment using optical in situ observation. In addition to these experiments, we investigated PO₄ effect into growth and dissolution dynamics of vaterite intermediate phases.

     We discovered not only these intermediate phases were very similar to vaterite and ACC, but also there were obvious difference between their chemical compositions and structures. For example, C/Ca rate of the intermediate phases were higher than vaterite, SAED patterns corresponding to C-Ca bonds were very weak compare to that of vaterite. In dissolution experiment, this intermediate phase revealed small responsive toward to PO4 compare to outer vaterite. This difference was strongly affected dynamics, growth and dissolution process in PO₄ presence conditions.

     Here, we will present about the details of vaterite intermediate phase structures and chemical compositions which were each ranging parts, growth and dissolution rate of each phase in various concentration of PO. In addition to reports about these intermediate phases, we will also introduce a formation of vaterites with unique morphologies during phase transformation based on in situ observation.

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