what is a fire opal
About Fire Opal-History and Introduction. Fire opal is a gem-quality form of amorphous hydrated silicon dioxide with no crystalline structure. Like other opal gemstones, between three and ten percent (and in some cases as much as 21 percent) of the weight of fire opal is water.nlike most opal, fire opal occurs with good transparency and because of this, it is usually faceted rather than cut en cabochon. On the other hand, brownish fire opal is usually cut en cabochon to enhance and maximize its desirable play of color effect.