**6.2. Anionic substitution at X-site**

Pentavalent arsenic, vanadium and chromium substitution can completely replace phospho‐ rus in calcium, strontium and barium fluor- and chlorapatites. Calcium fluor-vanadate, arsenate and -chromate structures were distorted compared to normal hexagonal apatite. Manganese completely replaced phosphorus only in barium apatites, while chromium and manganese could not be incorporated into lead apatites. Excluding these exceptions, contin‐ uous solid solutions were formed between the phosphate and/or vanadate and the chromate or manganese analogues for given divalent and halide ions [54]. The substitution of CO3 2− ions at X- (carbonate-apatite of A-type) and Z-site (carbonate-apatite of B-type) was already described in **Section 4.6.**
