Comparison between the absorption indices derived for spinels with different transtion metal content. The solid line refers to our sample – with an Fe content of 1.2% and a Cr content of 0.87%. The dotted line refers to a very Fe-rich sample (Fe-content of 11.1%), the dashed line denotes an Fe-poor sample (both according to Lenaz et al. 2008). The Fe content of the samples clearly correlates with the respective k-values at 2 μm.