# Together, which ions form hydroxyapatite crystals of osseous tissue?

Are these not $\text{calcium, phosphate, and hydroxyl ions.......}$
$\text{Hydroxylapatite,}$ $C {a}_{5} {\left(P {O}_{4}\right)}_{3} \left(O H\right)$, is a neutral salt, and contains $5 \times C {a}^{2 +} + 3 \times {\left(P {O}_{4}\right)}^{3 -} + H {O}^{-}$ ions, i.e. a neutral charge as required.