  The study of scattering and extinction properties of possible nanodiamond
grains in the ISM are reported. Calculations using Discrete Dipole
Approximation (DDA) for varying ellipsoidal shapes and sizes from 2.5 to $10
nm$ are considered. Nanodiamonds show negligible extinction from IR to near-UV
and very sharp far-UV rise. Comparison with observations rule out possibility
of independent nanodiamond dust but point towards possibility of nanodiamonds
as a component in the ISM. Radiation induced transformations may lead to
carbonaceous grains with different core and mantles. So calculations are also
performed for a core-mantle target model with nanodiamond core in graphite
mantles. The graphite extinction features get modified with the peak at 2175
\AA{} being lowered, broadened, blue shifted and accompanied by enhanced
extinction in the far-UV. Such variations in the 2175 \AA{} band and
simultaneous far-UV rise are observed along some sources. A three component
dust model incorporating silicate, graphite and graphite with nanodiamond core
is also considered. The model extinction compares very well with the average
galactic extinction in the complete range from 0.2 to $10 \mu m^{-1}$. The best
fit requires small size and small number of nanodiamonds.
