Absorption and extinction efficiencies for silicate and silicate core- ice mantle grains are presented for olivine-type particles in the wavelength range 0.07 $mu$-10$sup 3$ $mu$, for fused quartz-type particles in the range 0.056 $mu$-10$sup 3$ $mu$, and for lunar silicate-type particles in the range 1 $mu$-10$sup 3$ $mu$. Comparison with the observed near-infrared absorption spectrum in the BN object shows that no single type of these particles can adequately account for the observed 9.8 $mu$ feature, and that a mixture of various types of silicates may be required. Fits to the relative strengths of the observed ice and silicate features give mantle-to-core volume ratios from 0.3 to 1.3. The emission efficiency at wavelengths approximately-greater-than100 $mu$ is found to be sensitive to the presence of an ice mantle with the silicate grains following approximately a lambda$sup -2$ law, while the core-mantle grains follow a lambda$sup -3$ law. Upper limits to the enhancement of the far-infrared emissivity due to impurities are deduced, and it is found that only core-mantle grains can reasonably account for the observed far-infrared luminosities of many H ii regions. Extinction curves for silicate and silicate core-mantle grains are compared with observation, and it is found that other typesmore » of particles than silicate core-mantle particles must account for the ultraviolet extinction as well as for much of the visible extinction. Equilibrium grain temperatures are calculated for regions of no shielding, and are found to range from about 10 K to about 20 K for grain radii 0.1 $mu$ to 0.25 $mu$.« less