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 ( Al _ { 2 } O _ { 3 } ) 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 \pm 1.4 ) % of the identified dust mass , while corundum takes up ( 38 \pm 3 ) wt. % .
Depending on the choice of continuum , a range of mass fractions is observed for periclase ranging from ( 2.7 \pm 1.7 ) % in the most conservative case to ( 9 \pm 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 \pm 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 .