Table 1

Radius and Site Occupancy of Common Impurity Cations in Apatites

CationCa1 site: IXCa2+ (Å)Ca2 site: VIICa2+ (Å)Site preferenceReference
Ca2+1.181.06Stoichiometric
Sr2+1.311.21Ca2 (almost exclusively)1, 2, 3
Ba2+1.471.38Ca24
Mg2+0.89 (VIII)0.72 (VI)Possibly Ca1 in REE-rich enviroment5
Mn2+0.96 (VIII)0.9Ca1 (may negatively correlate with Cl content)6, 7, 8, 9
Fe2+0.92 (VIII)0.78 (VI, HS)Ca1 or Ca2 in Fe-poor environment10
Eu2+1.31.2Ca2 (similar behavior to Eu3+)2, 11, 12
Pb2+1.351.23Ca213, 14
Na+1.241.12Ca115, 16
Y3+1.0750.96Ca22, 11, 12
REE3+ (La-Lu)1.042–1.2160.925–1.10Ca22, 11, 12
Th4+1.090.94 (VI)Ca1 or Ca217
U4+1.050.95Ca1 or Ca217
Zr4+0.890.78Incompatible18
  • Cation radii data are from Shannon (1976), site preference references: 1 = Sudarsanan and Young (1974), 2 = Hughes et al. (1991), 3 = Rakovan and Hughes (2000), 4 = Khudolozhkin et al. (1973), 5 = Ito (1968), 6 = Ryan et al. (1972), 7 = Warren and Mazelsky (1974), 8 = Ercit et al. (1994), 9 = Miles et al. (2014), 10 = Khudolozhkin et al. (1974), 11 = Fleet and Pan (1995), 12 = Fleet et al. (2000), 13 = Engel et al. (1975), 14 = Verbeeck et al. (1981), 15 = Fleet and Pan (1997), 16 = Sha et al. (1999), 17 = Baumer et al. (1983), 18 = Prowatke and Klemme (2006)