A common material for read–write sliders is a composite of alumina (Al2O3) and titanium carbide (TiC), with a grain size of the order of 1 μm. I derive the effective complex reflectivity of this material, using scalar diffraction theory and the known indices of refraction of Al2O3 and TiC. The effective reflectivity is a function of the relative surface area of the exposed TiC grains as well as of the numerical aperture of the collection optics. The theory resolves several known discrepancies between ellipsometry and reflectometry of Al2O3–TiC. The theory also predicts a systematic error in the phase shift on reflection calculation. These results are of considerable interest for surface shape metrology of the slider as well as for optical flying-height testing and control of pole-tip recession.