  We present new imaging polarimetric observations of two Main Belt asteroids,
(234) Barbara and (387) Aquitania, taken in the first half of 2008 using the
Dual-Beam Imaging Polarimeter on the University of Hawaii 2.2 meter telescope,
located on Mauna Kea, Hawaii. Barbara had been previously shown to exhibit a
very unusual polarization-phase curve by Cellino, et al. (2006). Our
observations confirm this result and add Aquitania to the growing class of
large inversion angle objects. Interestingly, these asteroids show spinel
features in their IR spectra suggesting a mineralogical origin to the phase
angle-dependent polarimetric features. As spinel is associated with
calcium-aluminum-rich inclusions and carbonaceous chondrites, these large
inversion angle asteroids may represent some of the oldest surfaces in the
solar system. Circular as well as linear polarization measurements were
obtained but circular polarization was not detected.
