Apatite, Ca5(PO4)3(OH), belongs to a mineral group with a wide variety of end-members whose formulas can be generalized as follows: A5(BO4)3(C). What element substitutions might occur for Ca in the A site? What element substitutions might occur for P in the B site? What element substitutions may occur for OH in the C site? Reason from the atomic radii and charge considerations and justify your answers