Opalescence:The opalescence of a gemstone is its play of color, or the way in which it appears to change color when viewed from different angles. Opalescence is caused by the diffraction of light as it passes through the stone’s microcrystalline structure. The most common type of opalescence is iridescence, which is caused by the interference of light waves reflecting off of different layers of the stone. Other types of opalescence include chatoyancy (caused by light reflecting off of inclusions in the stone) and adularescence (caused by light reflecting off of parallel planes in the stone).