Ivory

Ivory, opaque, creamy white, hard, fine-grained, modified dentine that composes the upper incisor teeth (tusks) of an elephant. Ivory is composed of curved layers of dentine alternating in shade, that intersect one another; the resulting lozenge-shaped structure is elastic and finely grained. The layers of a tusk are deposited from the central pulp, so that the innermost layer is the newest.

Most commercial elephant ivory is obtained from the tusks of the African elephant, mainly from eastern and central Africa. (Most of the ivory of the western half of Africa is hard, whereas that from the eastern half is soft. Hard ivory is relatively glassier in texture, more difficult to cut and more susceptible to cracking than soft ivory.) Less than one-quarter of commercial ivory is obtained from freshly killed elephants; the remainder is obtained from the carcasses of elephants that died natural deaths. Fossil ivory, called odontolite, is a blue variety that is found in small quantities in the frozen soil of northern Siberia. Odontolite was produced by the mammoths of the Pleistocene geological epoch; its blue colour results from saturation by metallic salts.

Carved ivory has been used for decorative purposes since the time of the ancient Egyptians (see Ivory Carving). Small pieces of ivory are used for high-quality furniture inlays, chess pieces, and small jewellery. Larger pieces of ivory sometimes have been used in the manufacture of billiard balls, piano keys, and toilet articles. During the late 1980s, as Africa's elephant herds declined, environmentalists led a worldwide effort to shut down the ivory trade; in 1989 the United States and the European Community (now called the European Union) banned all ivory imports.

Tusks of several other animals such as hippopotamuses, narwhals, sperm whales, and walruses are commonly called ivory and have similar physical properties, and numerous plastic substitutes for ivory have been developed. Several ivorylike vegetable parts are also used in imitation of ivory; the ivory palm, for example, produces large, white, hard seeds, called ivory nuts, the endosperm of which is commonly known as vegetable ivory.