Opals are semi-precious stones that are luminous and iridescent, frequently with inclusions of many colors ("fire"). There are three major types of opals: common opal, opalescent precious opal (white or black, with a rainbow-like iridescence caused by tiny crystals of cristobalite) & fire opal (a milky stone that is fiery orange to red in color with no opalescence). Generally, opal with red fire is the most valued because opal that shows red will also show other colors when rolled back and forth: it contains the whole spectrum. The pattern of the play of color also influences value. Generally large flashes and broad patterns are more rare and valuable than small pinfire patterns.