# What is the formula for the compound composed of calcium and phosphate?

$C a H P {O}_{4}$ or $C {a}_{3} {\left(P {O}_{4}\right)}_{2}$
Calcium phosphates are a very broad church. I just read that the mineral apatite, which is the phosphate we put on our gardens as fertilizer is $C {a}_{5} {\left(P {O}_{4}\right)}_{3} X$ $\left(X = {X}^{-} , H {O}^{-}\right)$.
Of course the phosphate ion, $P {O}_{4}^{3 -}$ is quite a strong base, and in aqueous solution exists as $H P {O}_{4}^{2 -}$.