Opal’s shifting play of kaleidoscope colors is known as play-of-color. Play-of-color occurs when sub-microscopic sheres of silica, stacked as uniform layers of balls, diffract (bend) light into the spectral colors of the rainbow. This is true of all opals that exhibit play-of-color. When opal has a translucent to semi-translucent white or light background color it is known as white opal. Opal is one of the birthstones for October and is designated for the 14th wedding anniversary. White opal is mined primarily in Australia.