Grazing-incidence XAFS spectroscopy was applied to study the sorption of Zn(II) on two crystallographically distinct surfaces of highly polished sapphire single crystals as a simplified analog for metal ion sorption on natural aluminum-(hydr)oxides. Experiments were performed both in situ (in contact with bulk solution) and ex situ in a humidified N-2 atmosphere. The identification of an Al shell at roughly 3 Angstrom in all samples indicates that Zn(II) binds as an inner sphere complex on both the (0001) and (1-102) surfaces. The first shell Zn-O distances of 1.97-1.99 Angstrom suggest that Zn is in fourfold coordination with oxygen in the in situ samples. However, sample drying appears to have induced the formation of polynuclear surface complexes with first shell Zn-O distances closer to values expected for sixfold coordination (2.06-2.07 Angstrom ). The results presented here show that in situ characterization of sorption products on single crystal surfaces using Grazing-incidence XAFS is feasible if solution conditions are chosen carefully.