Dust in the wind: Crystalline silicates, corundum, and periclase in PG 2112+059

We have determined the mineralogical composition of dust in the broad absorption line ( BAL) quasar PG 2112 + 059 using mid- infrared spectroscopy obtained with the Spitzer Space Telescope. From spectral fitting of the solid state features, we find evidence for Mg- rich amorphous silicates with olivine stoichiometry, as well as the first detection of corundum (Al2O3) and periclase (MgO) in quasars. This mixed composition provides the first direct evidence for a clumpy density structure of the grain- forming region. The silicates in total encompass 56.5% +/- 1.4% of the identified dust mass, while corundum takes up wt.%. Depending on the choice 38 +/- 3 of continuum, a range of mass fractions is observed for periclase ranging from 2.7% +/- 1.7% in the most conservative case to 9% +/- 2% in a less- constrained continuum. In addition, we identify a feature at 11.2 mu m as the crystalline silicate forsterite, with only a minor contribution from polycyclic aromatic hydrocarbons. The 5% +/- 3% crystalline silicate fraction requires high temperatures such as those found in the immediate quasar environment in order to counteract rapid destruction from cosmic rays.