Precious Opal
Pictures of Precious Black Opal and White Opal

Precious opal is a hydrous silicon dioxide material that flashes iridescent colors when it is viewed from different angles, when the stone is moved or when the light source is moved. This phenomenon is know as a "play of color" or an "opalescence". Most precious opals will flash a number of colors such as bright yellow, orange, green, blue, red or purple. Play of color is the characteristic of opal that makes it such a popular gem. The desirability of opal is based upon color Intensity, diversity, uniformity, pattern and ability to be seen from any angle. The stone at right is a black opal from Lightning Ridge, Australia. The stone below is is a precious opal from the Constellation Mine near Spencer, Idaho.