We construct a quasar extinction curve based on the blue and red composite quasar spectra of Richards et al .
( 2003 ) prepared from the SDSS survey .
This extinction curve does not show any traces of the 2200 Å feature characteristic of the Interstellar Medium , and this indicates that graphite grains are likely absent close to quasar nuclei .
The extinction is best modeled by AC amorphous carbon grains , assuming a standard distribution of grain sizes ( p = 3.5 ) but slightly larger minimum grain size ( a _ { min } = 0.016 \mu m ) and lower maximum grain size ( a _ { min } = 0.12 \mu m ) than the respective canonical values for the interstellar medium .
The dust composition is thus similar to that of the dust in AGB stars .
Since graphite grains form from amorphous carbon exposed to strong UV irradiation the results indicate that either the dust forms surprisingly far from the active nucleus or in a wind that leaves the nucleus quickly enough to avoid crystallization into graphite .