When not found with fossil bone, gastroliths (fossil gizzard stones) may be hard to identify. One attribute that is potentially useful is their high degree of surface polish, presumably caused by abrasion in the animal's gizzard. A novel video laser light scattering instrument is used to characterize the surface roughness of suspected moa gastroliths, as well as similar (non-gastrolith) quartz rocks that were polished by ocean waves. The instrument is fairly successful at distinguishing between the two types of samples.