Biominerals, including calcium carbonates, are found in a range of organisms. Although amorphous calcium carbonate (ACC) is inherently unstable, it is a key material in biomineralisation of calcium carbonate. Magnesium ions in ACC and amorphous magnesium carbonates (AMC) are thought to enhance stability. However, a close structural comparison between ACC and AMC has not been made. Recently synthetic AMC prepared has been hailed as an "impossible material" due to it having exceptional porosity. The goal of the present proposal to use the measurement of neutron diffraction structure factors for AMC to build a detailed atomistic model of AMC.