  Interplanetary dust (IPD) is thought to be recently supplied from asteroids
and comets. Grain properties of the IPD can give us the information about the
environment in the proto-solar system, and can be traced from the shapes of
silicate features around 10 $\mu$m seen in the zodiacal emission spectra. We
analyzed mid-IR slit-spectroscopic data of the zodiacal emission in various sky
directions obtained with the Infrared Camera on board AKARI satellite. After we
subtracted the contamination due to instrumental artifacts, we have
successfully obtained high S/N spectra and have determined detailed shapes of
excess emission features in the 9 -- 12 $\mu$m range in all the sky directions.
According to a comparison between the feature shapes averaged over all
directions and the absorption coefficients of candidate minerals, the IPD was
found to typically include small silicate crystals, especially enstatite
grains. We also found the variations in the feature shapes and the related
grain properties among the different sky directions. From investigations of the
correlation between feature shapes and the brightness contributions from dust
bands, the IPD in dust bands seems to have the size frequency distribution
biased toward large grains and show the indication of hydrated minerals. The
spectra at higher ecliptic latitude showed a stronger excess, which indicates
an increase in the fraction of small grains included in the line of sight at
higher ecliptic latitudes. If we focus on the dependence of detailed feature
shapes on ecliptic latitudes, the IPD at higher latitudes was found to have a
lower olivine/pyroxene ratio for small amorphous grains. The variation of the
mineral composition of the IPD in different sky directions may imply different
properties of the IPD from different types of parent bodies, because the
spatial distribution of the IPD depends on the type of the parent body.
