CHAOTIC GRANULAR MIXING has been observed for the first time. Studies of chaos in the mixing of fluids is common, but it was thought that grains mixed by a combination of steady motion and diffusion. Now an experiment by Troy Shinbrot, Fernando Muzzio, and Albert Alexander at Rutgers (shinbrot@sol.rutgers.edu, 732-445-6710), using identical (initially segregated) red and green particles in a cylindrical drum being gently tumbled, shows that grains can spontaneously interpenetrate chaotically, and the green-red interface was fractal in nature. Even more unexpected was the speed at which the interface grew in complexity---many orders of magnitude greater than expected. These results should have an impact on the mixing industry, which worries about how long and how hard to mix commodities such as pharmaceuticals, explosives, makeup, and powdered foods. (Troy Shinbrot et al., Nature, 25 February 1999; see figure at Physics News Graphics.)