Abstract
Using surface x-ray diffraction, we have determined the atomic structure
of the {010} interface of brushite, CaHPO4·2(H2O), with water. Since
this biomineral contains water layers as part of its crystal structure,
special ordering properties at the interface are expected. We found that
this interface consists of two water bilayers with different ordering properties.
The first water bilayer is highly ordered and can be considered as part
of the brushite crystal structure. Surprisingly, the second water bilayer
exhibits no in-plane order, but shows only layering in the perpendicular
direction. We propose that the low level of water ordering at the interface
is correlated with the low solubility of brushite in water.