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We have determined the mineralogical composition of dust in the BroadAbsorption Line (BAL) quasar PG 2112+059 using mid-infrared spectroscopyobtained with the Spitzer Space Telescope. From spectral fitting of the solidstate features, we find evidence for Mg-rich amorphous silicates with olivinestoichiometry, as well as the first detection of corundum (Al_2O_3) andpericlase (MgO) in quasars. This mixed composition provides the first directevidence for a clumpy density structure of the grain forming region. Thesilicates in total encompass 56.5% of the identified dust mass, while corundumtakes up 38 wt.%. Depending on the choice of continuum, a range of massfractions is observed for periclase ranging from 2.7% in the most conservativecase to 9% in a less constrained continuum. In addition, we identify a featureat 11.2 micron as the crystalline silicate forsterite, with only a minorcontribution from polycyclic aromatic hydrocarbons. The 5% crystalline silicatefraction requires high temperatures such as those found in the immediate quasarenvironment in order to counteract rapid destruction from cosmic rays.

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