Aluminum is highly abundant in the Earth's crust where it is present in a wide variety of primary and secondary aluminosilicate minerals, amorphous phases, and aqueous solution species. The speciation and coordination of AI in many of these phases, particularly those that are X-ray amorphous or present as thin surface coatings, are often unknown or based on indirect methods. We have utilized aluminum K-edge XANES in a study of the nature of several such phases, specifically the aluminum rich phases present in soils on the surfaces of quartz and feldspar grains in loess, and aluminum substitution in iron oxyhydroxides.In addition, the sorption products of AI-(oxy)hydroxides on synthetic t~-A1203 (0001) surfaces were investigated along with model compounds. Analysis of our data suggests that the Al-rich surface phase on quartz grains in loess is gibbsite-like, while AI sorbed on synthetic quartz is boehmitelike. Surprisingly, AI substituted in goethite appears to be more similar to gibbsite than to diaspore, which is isostructural with goethite. The experimental data for corundum and Linde alumina show good agreement with calculated AI K-edge spectra from a developmental version of the full multiple scattering code FEFF8 using clusters of up to 66 atoms