  As pointed out by Lingenfelter and Ramaty (1977), the shapes of some
gamma-ray lines produced by cosmic-ray interactions with the interstellar
medium potentially contain valuable information on the physical properties of
dust grains, including their compositions and size distributions. The most
promising of such lines are at 847, 1369, 1779 and 6129 keV, from 56-Fe*,
24-Mg*, 28-Si* and 16-O*, respectively. We performed detailed calculations of
their profiles using, in particular, available laboratory measurements combined
with optical model calculations to evaluate the energy distributions of the
recoiling excited nuclei. We show that the line shapes are mainly sensitive to
relatively large interstellar grains, with radii greater than 0.25 microns.
Line fluxes from the inner Galaxy are then predicted.
