Brazil nut
The seed of Bertholletia excelsa, a large tree of the Amazon rainforest; the seeds grow packed like segments inside a hard woody fruit, and the nut is known for its very high selenium content.
When you shake a container of mixed-size granules, larger ones rise and smaller ones sink—the 'Brazil nut effect.' Concrete mixers keep spinning during transport partly for this reason: without mixing, vibrations cause cement, sand, and gravel to separate by size.
0