Structure and dynamics of amorphous carbonates related to biomineralization : a neutron diffraction study Amorphous calcium carbonate(ACC) is a wide spread biological material found in many organisms such as sea Urchins and mollusks where it serves as either a precursor phase for the crystalline biominerals or is stabilized and used in the amorphous state. As ACC readily crystallizes stabilizers such as anions cations or macromolecules are often present to avoid or delay unwanted crystallization. Furthermore additives often control the properties of the materials to suit the specific function needed for the organism. E.g. cystoliths in leaves that scatter light to optimize energy uptake from the sun or calcite aragonite crystals used in protective shells in mussels and gastropods. Lifetime of the amorphous phase is controlled by the kinetic stability against crystallization. This has often been linked to water which plays a role in the mobility of ions and hence the probability of forming crystalline nuclei to initiate crystallization. However it is unclear how the water molecules are incorporated within the amorphous phase either as liquid confined in pores as structural water binding to the ions or as a mixture of both. It is also unclear how this is perturbed when additives are added especially Mg2+ one the most common additives found in biogenic samples. [...]