Polarization of 95 stars according to the remaining dust phase abundance of Fe as given by Eq. (1) normalized to the cosmic abundance of iron. Halo stars with |b| > 30° and disk stars with |b| ≤ 30° and low (E(B − V) ≤ 0.2) and high (E(B − V) > 0.2) reddening are shown with different symbols. Filled symbols correspond to sightlines where the abundances of three elements (Mg, Si, and Fe) are measured. Open symbols correspond to sightlines where the abundances of two elements (Fe and Mg or Si) are known. The number of stars is indicated in parentheses in the legend.