Rotate the disk and see new sand patterns forming for the next 30 minutes. Students will study it for hours. Great for sedimentary rock formation discussions! Why do some particles seem to form boundary layers between other type of particles. The gold particles seem to always come together in a line, much like a vein of gold found in nature. It is fascinating to observe the flow patterns in the liquid. The final layering is due to differences in particle shape, size, and density. Stand included. Colors may vary. Approx. 10 inch round.