University of Colorado

Mineral Structure Data

Apatite Group

The apatite group is composed of minerals of the general formula Ca5(PO4)3(OH,F,Cl).

The crystal structure of apatite.


Table 9.6.1. Apatite Group Unit Cells.


End-Member       Hydroxyapatite       Fluorapatite       Chlorapatite

Formula         Ca5(PO4)3OH         Ca5(PO4)3F         Ca5(PO4)3Cl

Form.Wt.         502.322              504.313            520.767
Density          3.153                3.201              3.185
Mol Volume       159.334              157.527            163.527

Z                2                    2                  2
Cryst.Sys.       Hexagonal            Hexagonal          Hexagonal
                             
Cryst.Class      6/m                 6/m                 6/m
Space Group      P63/m                P63/m                P63/m

Cell Parameters
a                9.424                9.367              9.628
c                6.879                6.884              6.764

Vol.             529.09               523.09           543.01

Ref.             Sudarsanan and         Sudarsanan         Mackie et al.
                 Young(1969)         et al.(1972)         (1972)


Table 9.6.2. Apatite Group Ca Sites.

End-Member               Hydroxyapatite                        Fluorapatite                       Chlorapatite

Site         Ca1         Ca2         Ca1         Ca2         Ca1         Ca2
C.N.         9         8         9         7         9         8

Point Sym.         3         m         3         m         3         m
Wyckoff Not.         4f         6h         4f         6h         4f         6h

Frac.Coord.
x         1/3         .2465         1/3         .2416         1/3         .2596
y         2/3         .9931         2/3         .0071         2/3         .0053
z         .0013         1/4         .0012         1/4         .0038         1/4

Distances
O1         (3)2.407         (1)2.705         (3)2.397         (1)2.814         (3)2.398         (1)2.973
O2         (3)2.452         (1)2.357         (3)2.453         (1)2.384         (3)2.448         (1)2.295
O3         (3)2.805         (2)2.344         (3)2.801         (2)2.384         (3)2.789         (2)2.534
O3                  (2)2.512                  (2)2.398                  (2)2.336
OH/F/Cl                  (2)2.383                  (1)2.231                  (2)2.801



Mean         2.555         2.443         2.550         2.428         2.545         2.577
sigma         .189         .127         .190         .180         .184         .255



Poly.Vol.         31.974         26.138         31.750         21.506         31.977         34.126



Site Energy         -969.         -1009.         -984.         -996.         -984.         -976.


Table 9.6.3. Apatite Group P Sites.


End-Member         Hydroxyapatite         Fluorapatite         Chlorapatite

C.N.         4         4         4

Point Sym.         m         m         m
Wyckoff Not.         6h         6h         6h

Frac.Coord.
x         .3983         .3981         .4078
y         .3683         .3688         .3754
z         1/4         1/4         1/4

Distances
O1         1.537         1.534         1.536
O2         1.545         1.541         1.542
O3(2)         1.529         1.534         1.529

Mean         1.535         1.536         1.534
sigma         .008         .003         .006

Poly.Vol.         1.853         1.857         1.849
Q.E.         1.0011         1.0008         1.0017
Ang.Var.         4.3         3.7         7.1

Site Energy         -6831.         -6835.         -6834.



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