The dynamics of bone mineral in some vertebrates.

In the literature octocalcium phosphate as well as brushite have been proposed as the precursor phase for bone mineral in the higher vertebrates. In this study it is shown that the situation is more complex. A sodium and carbonate containing apatite (NCCA) and a magnesium whitlockite (MWH) are present from the beginning of mineralization together with octocalcium phosphate. Upon further bone development the NCCA and the MWH phase are deposited in amounts proportional to the amount of mineral deposited. However, the octocalcium phosphate is transformed slowly in a heavily carbonated defective hydroxyapatite. From the available experimental data it can be derived that the time of this transformation is smaller than four weeks under in vivo conditions.