Fire opal is an unusual variety of opal from Mexico, with colors ranging from yellow to orange and orange-red. Like the familiar opal, the fire opal is hydrated silicon dioxide. But unlike the traditional opal, many Mexican opals are clear enough for facets.
Play of color, body color and transparency are the three criteria which determine the price of a fire opal. The more transparency and 'fire' it has, and the more intense the deep red of its body color, the more valuable it will be. The rarest, and thus the most highly esteemed, is the intense orange-red fire opal from Mexico with its strong play of color.