The solubilities of apatites of varying compositions were measured as a function of pH in seawater at 10° and 25°C. Wide ranges of solubilities were observed; at pH = 7.4 they ranged from 0.4 to 11 µM PO4‐P liter−1, depending on the nature of the samples. Results are interpreted in terms of complex coatings formed on the surface of the apatites.