Surah 55. Ar-Rahman, Ayah 22

Pearls are produced by the oyster and coral by the polyp, a minute marine creature, which, working in millions, has by its secretions produced the reefs, islands, and banks in and on both sides of the Red Sea and in other parts of the world. The pearl has a translucent lustre, usually white, but sometimes pink or black. Coral is usually opaque, red or pink, but often white, and is seen in beautiful branching or cup-like shapes as visitors to Port Sudan will recall. Both are used as gems and stand here for gems generally. Mineral gems, such as agate and cornelian, are found in river-beds. Pearl oysters are also found in some rivers.