  The composite grain is made up of a host silicate spheroid and graphite
inclusions. The extinction efficiencies of the composite spheroidal grains for
three axial ratios are computed using the discrete dipole approximation (DDA).
The interstellar extinction curve is evaluated in the spectral region
3.40--0.10$\mu m$ using the extinction efficiencies of the composite spheroidal
grains. The model extinction curves are then compared with the average observed
interstellar extinction curve. We also calculate the linear polarization for
the spheroidal composite grains at three orientation angles and find the
wavelength of maximum polarization. Further, we estimate the volume extinction
factor, an important parameter from the point of view of cosmic abundance, for
the composite grain models that reproduce the average observed interstellar
extinction. The estimated abundances derived from the composite grain models
for both carbon and silicon are found to be lower than that are predicted by
the bare silicate/graphite grain models but these values are still higher than
that are implied from the recent ISM values.
