The term 'iridescent stone' can be summarized as a gemstone that displays a rainbow-like effect. The most common example of this is the OPAL, which is a 4-letter word. Opals are composed of silica and water, and they come in a variety of colors, including white, black, and pink. They are known for their unique play of color, which is caused by the diffraction of light through the stone's layers.