Fig. 5. X-ray crystal structure of fluorapatite, the phosphate mineral Ca5(PO4)3F, showing (A) 2 × 2 unit cells, and (B) a column of F− ions. Each F− ion is bonded to F− ions above and below it (F–F 3.44 Å) and to 3 Ca2+ ions (F–Ca 2.463 Å) which form a triangle around it. Ca, grey; P, yellow; O, red; F, green. (A) is reproduced and (B) adapted from ref. 29 with permission from AO Research Institute Davos, copyright 2001.29.
