  The broad absorption bump at 2175 angstrom due to dust, which is ubiquitous
in the Galaxy and is seen in the Magellanic clouds, is also seen in a composite
spectrum of Mg II absorbers. The composite absorber spectrum is obtained by
taking the geometric mean of 92 quasar spectra after aligning them in the
restframe of 96 absorbers. By aligning the spectra according to absorber
redshifts we reinforce the spectral features of the absorbers, and smooth over
possible bumps and wiggles in the emission spectra as well as small features in
the flat fielding of the spectra. The width of the observed absorption feature
is 200-300 angstrom (FWHM), or 0.4-0.6 (micron)^{-1} and the central wavelength
is 2240 angstrom. These are somewhat different from the central wavelength of
2176 angstrqom and FWHM=0.8-1.25 (micron)^{-1} found in the Galaxy. Simulations
show that this discrepancy between the properties of the 2175 angstrom feature
in Mg II absorbers and Galactic ISM can be mostly explained by the different
methods used to measure them.
