The fluoride content of phosphorites and marine waters indicates that there is a strong partitioning of fluoride in favor of apatite. However, synthesis of fluorapatite at low temperatures required solutions enriched 102 to 103 in fluoride relative to sea water. Uptake of fluoride by sodium-bearing hydroxylapatite requires similarly enriched solutions, and with the uptake there is a concomitant release of sodium and phosphate from the crystals.
Agitation of Durango fluorapatite with water resulted in fluoride increasing to a pF~3 and hydroxyl to pOH~4.5 in the solution. A surface layer retards the exchange of hydroxyl and fluoride in apatite.