Corpora arenacea

Corpora arenacea (or brain sand) are calcified structures in the pineal gland and other areas of the brain such as the choroid plexus. Older organisms have numerous corpora arenacea, whose function, if any, is unknown. They are sometimes, used as anatomical landmarks in radiological examinations.

Chemical analysis shows that they are composed of calcium phosphate, calcium carbonate, magnesium phosphate, and ammonium phosphate. . Recently, calcite deposits have been described as well.

Concentrations of "brain sand" are said to increase with age.