Precious opal: Black and white precious opal from Australia.
What is Precious 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. In the photo shown here, the stone on the left is a black opal from Lightning Ridge, Australia. The stone on the right is a precious opal from the Coober Pedy, Australia.