Kiribati, formerly the Gilbert Islands, consists of three widely separated main groups of southwest Pacific islands: the Gilberts on the equator, the Phoenix Islands to the east, and the Line Islands farther east. Ocean Island, producer of phosphates until it was mined out in 1981, is also included in the 2 million square miles of ocean. Most of the islands of Kiribati are low-lying coral atolls built on a submerged volcanic chain and encircled by reefs.