Heating rates of a 10 Å silicate grain as a function of the radial distance are shown for two inclination angles, θ = 30°, 75°, subjected to radiative heating by the central source and collisional heating by the ambient gas. For both cases the figure shows that, owing to the low densities of the gas, the collisional heating is found to be negligible, compared to the rate of radiative energy absorption.