  In the framework of the silicate core-carbonaceous organic mantle
interstellar dust model, the bulk of the visual/near-IR extinction and the
entire polarization are from nonspherical and aligned core-mantle grains. The
3.4 micron C-H and 9.7 micron Si-O absorption features, respectively arising
from the hydrocarbon mantle and the amorphous silicate core, are expected to be
polarized to a modestly different degree. Spectropolarimetric observations
toward the same lines of sight both in the 3.4 micron region and in the 9.7
micron region would be of great value to test the core-mantle dust model. The
fact that the 3.4 micron feature is not polarized along the line of sight
toward the Galactic center source IRS 7 is not yet sufficient to reject the
core-mantle model due to the lack of spectropolarimetric observation of this
region in the 9.7 micron region.
