Mexican Fire Opal is a type of crystal opal that shows magnificant flashes of red/orange color. Unlike most opals, fire opal is usually faceted so that you get sparkle in addition to vibrant color. Fire opal was born in fire in the ancient volcanoes of Mexico. It forms when water seeps into silica-rich lava, filling seams and hollows. Under heat and pressure, the silica forms a solid gel that traps the remaining water within its structure. Fire opal that displays play-of-color is rare because volcanic opal forms relatively quickly and the spheres of silica rarely have time to settle into the diffraction grids that create play-of-color.