SAM OGDEN / SCIENCE PHOTO LIBRARY SAM OGDEN / SCIENCE PHOTO LIBRARY
Grain layers. Separate layers of different grains formed after they were poured as a homogenous mix- ture, an effect seen during the formation of sedi- mentary rocks such as sandstone. A mixture of sand & red sugar was poured between 2 vertical sheets of glass. The mixture formed a mound whose sides periodically reached a critical angle, causing an avalanche. The smooth grains of sand stopped short of the kink at the bottom of the heap, whilst the bigger, rougher sugar grains went a bit further. As more grains fall the kink rides upward, forming 2 layers. Each succeeding avalanche makes another pair of layers. This experiment was devised by Hernan Makse of Boston University, USA, in 1997.
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