When they are ripe, rudraksha stones are covered by an inedible blue outer fruit so they are sometimes called 'blueberry beads'.
Rudraksha ( IAST: rudrākṣa) refers to a stonefruit, the dried stones of which are used as prayer beads by Hindus (especially Shaivas), as well as by Buddhists, Sikhs, and Muslims. Rudraksha beads are the dried stones of the fruit of the Elaeocarpus ganitrus tree
