Fire opals are transparent to semi-transparent, resembling gelatin, with red, orange, or yellow body color, with or without play-of-color. The body color is caused by inclusions of iron oxides. They are also sometimes called Mexican opals because most of the best fire opals are found in Mexico. Opals are typically cut as cabochons or polished free-form to best show the play-of-color. This group of opals from Mexico range in weight from 11 to 143 carats.