Brazil nut

The brazil nut is the large edible seed of South American tree Bertholletia excelsa. It is one of a handful of commercially important nuts. The fruit of Bertholletia excelsa resembles a coconut and contains 8-24 seeds (brazil nuts). Brazil nuts were at one time also referred to as "nigger toes".

The Brazil Nut Effect refers to the phenomenom where big particles end up on the surface when a mixture of granular material is shaken. The term was based on the observation that when a can of mixed nuts is opened after it has been shook, the brazil nuts tend to be on top. The reason that the larger heavier particles end up on top (against intuition) is due to vibration-induced convection flow. When shook, the particles flow in a pattern; individual particles move up through the middle, across the surface, and down the sides (this pattern is convection flow). If a large particle is involved, it will be moved up to the top by convection flow. Once there it will stay since the convection currents are too narrow to sweep it down along the wall. The effect is of serious scientific interest for industrial seperation and mixing operations. The effect is also depends on the shape of a container. A cylinder such as a can of nuts works well, while a cone-shaped container results in what is known as the Reverse Brazil Nut Effect.