Now that the behavior of phosphate species in cryo-fixed solutions is determined, CaP mineralization can be studied with our sample preparation approach combined with low-temperature 31 P ssNMR. In particular, we investigated a case of fast CaP formation by mixing calcium and phosphate-containing solutions with equal initial concentrations of 50 mM at pH 7.4. The reaction proceeds rapidly, as precipitation of a white solid is seen immediately with the naked eye upon mixing. To investigate the very first steps of the reaction and their evolution, cryofixation of the mineralizing solution has been prepared after 20, 100 ms, and 1 and 60 seconds and studied by low-temperature 31 P CP MAS ssNMR (Figure ).