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Zircon [ZrSiO4]
Structure Tetragonal
Space Group I41/amd (No. 141)
a=b=6.6100 Å, c=6.0010 Å
a=b=g=90.00
Z=4
Atomic Positional Parameters
O 16h 0.0000 0.0646 0.1967
Zr 4a 0.0000 0.7500 0.1250
Si 4b 0.0000 0.2500 0.3750
Reference
Z Mursic, T Vogt, H Boysen and F Frey (1992)
Journal of Applied Crystallography,
25, 519-523
Mineral Chemistry
The structure of zircon consists of alternating (discrete) SiO4 tetrahedra and ZrO8 units sharing edges to form chains parallel to the c-direction. A number of elements may replace zirconium in the structure, including uranium, thorium, hafnium and rare earth elements. Zircon is a common accessory mineral in igneous rocks, and because of its stability, is also found in many sedimentary rocks. The minerals thorite (ThSiO4) and coffinite (U[SiO4]1-x(OH)4x) have the zircon structure. Zircons are used for radioactive age determinations by calculating Th/U, Pb/U or Pb isotope ratios.
The Chime figure shows zircons as crimson spheres, oxygens as red spheres, and silicons as ochre spheres. Each zirconium is surrounded by eight oxygens. The unit cell is shown with grey lines.