Intense infrared absorptions of small particles suspended in a dissimilar medium show effects that allow one to deduce, at least in principle, the morphology of the particles. These effects have their origins in the discontinuity in optical constants at the surface of the particle, and may be described analytically when the particles are spherical or ellipsoidal. This paper addresses the problems that arise when the particles under consideration are crystalline and have sharp edges and corners. Analytical descriptions are not available for such cases and it is shown that a numerical implementation the current standard electrostatic approach does not converge for cubes. However, convergence can be obtained by chamfering the edges and corners of the simulated particle. Experimental spectra are reported for suspended microcrystallites of sulfur hexafluoride and of carbon dioxide. The spectra were simulated using a variety of morphologies and it is concluded that the sulphur hexafluoride particles were cubes while the carbon dioxide particles were cuboctahedra.