Fluorapatite Ca₅(PO₄)₃F

Unit cell

Lattice constants

a = 9.373 Å, b = 9.373 Å, c = 6.883 Å; α = 90°, β = 90°, γ = 120°

Cell volume

523.6 ų

Atoms in the cell

42 (Ca 10, P 6, O 24, F 2)

Formula units Z

2

Calculated density

2.61 g cm⁻³

Shortest contact

1.532 Å

Coordination

Ca

CN 6 at 2.40 Å (5.4 O + 0.6 F)

P

CN 4 at 1.53 Å (4 O)

O

CN 1 at 1.53 Å (1 P)

F

CN 3 at 2.30 Å (3 Ca)

About the structure

• PO₄ tetrahedra and two kinds of Ca site build hexagonal channels along c; the F⁻ ions sit in the channels, each between three Ca²⁺.
• Replace F⁻ by OH⁻ and this is hydroxyapatite, the mineral of bone and tooth enamel; fluoride in toothpaste converts the surface to this harder, more acid-resistant form.
• Coordinates from the Crystallography Open Database, entry 2104744 (open data); hydrogen and water sites with partial occupancy below 0.5 are left out.

Atom positions (fractional, one cell)

Z, coordination numbers, distances, density and packing on this page are computed from these coordinates.