Short answers, pulled from the story.
Ivory is a hard, white material made mainly of dentin, one of the physical structures of teeth and tusks. It is composed of collagen fibers mineralized with hydroxyapatite, and natural ivory contains structures of mineralised collagen.
Elephant ivory is the most important source, but ivory also comes from mammoth, walrus, hippopotamus, sperm whale, orca, narwhal, and warthog. Elk also have two ivory teeth, believed to be the remnants of tusks from their ancestors.
The trade in natural ivory of threatened species such as African and Asian elephants is illegal because demand has seriously declined elephant populations. The Asian elephant was placed on CITES Appendix I in 1975, and the African elephant in January 1990, with CITES deciding to ban international trade in African elephant ivory in 1989.
The Wildlife Conservation Society has stated that the global ivory trade leads to the slaughter of up to 35,000 elephants a year in Africa. In the 1980s the African elephant population fell from 1.3 million to around 600,000 in ten years.
Ivory was valued since ancient times for carvings, false teeth, piano keys, fans, dominoes, billiard balls, cutlery handles, Scottish bagpipes, and buttons. It was also carved into netsuke, inro, official seals, kris dagger handles, and the faces and hands of Catholic icons.
Alternatives include fossil mammoth tusks frozen in the tundra, which have been traded legally for 300 years, and fossil walrus ivory from animals that died before 1972. Tagua, or vegetable ivory, is the seed of the ivory nut palm found in coastal rainforests of Ecuador, Peru, and Colombia, and ivory can also be produced synthetically.