This paper examines recently acquired polarimetric data of dry sand with a smooth air/sand interface at millimeter-wave (MMW) frequencies. The data characterize volume scattering from different types of sand as a function of the radar incidence angle, frequency, polarization, and particle size. The data show substantial volumetric response from dry sand at MMW frequencies with significant depolarization (between -12 and -7 dB). An empirical model is proposed and adapted for both smooth and 1-D periodic dry sand surfaces. Comparison between the expected volume scattering response of a dry sand medium with the surface scattering response of dry sand surfaces with rough interfaces shows that volume scattering is, in general, dominant, particularly at 95 GHz.