Hydroxyapatite Ca₅(PO₄)₃(OH)

Unit cell

Lattice constants

a = 9.417 Å, b = 9.417 Å, c = 6.875 Å; α = 90°, β = 90°, γ = 120°

Cell volume

527.9 ų

Atoms in the cell

44 (Ca 10, P 6, O 26, H 2)

Formula units Z

2

Calculated density

2.58 g cm⁻³

Shortest contact

1.085 Å

Coordination

Ca

CN 6 at 2.40 Å (6 O)

P

CN 4 at 1.53 Å (4 O)

O

CN 1 at 1.53 Å (0.92 P + 0.08 H)

H

CN 2 at 1.09 Å (1.5 O)

About the structure

• The mineral of bone and tooth enamel: the fluorapatite framework (also in this lab) with OH⁻ instead of F⁻ in the channels along c, the hydroxide sitting slightly off the mirror plane.
• Fluoride in toothpaste exchanges that OH⁻ for F⁻ at the surface, giving the more acid-resistant fluorapatite; synthetic hydroxyapatite is the standard bone-graft and implant-coating material.
• Coordinates from the Crystallography Open Database, entry 9001233 (open data); hydrogen and water sites with partial occupancy below 0.5 are left out. Some sites are partially occupied in the real crystal.

Atom positions (fractional, one cell)

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