Basic Requirements for Calcification

THE chief product of calcification in bone is usually considered to be a variant of hydroxyapatite, Ca10 (PO4)6 (OH)2 (ref. 1), the unit cell of the crystal lattice containing all eighteen ions of the formula. A tacit assumption is made that the two OH− ions come from the water in the calcifying solution. Because the equilibrium constant for water (Kw) is only 10−14 (mole/l.) (ref. 2) at 25° C, however, the dissociation of water would require more energy to increase the OH− concentration than is readily available in the surrounding mineral matter2.