Play-of-color in a noble opal

One of the most striking characteristics of certain opals is the play-of-color. Not all opals may show it; in fact, those that have play-of-color are considered “noble opals”. Opals are the gemological variety of hydrated amorphous silica, and they owe the play-of-color to the diffraction that occurs when light hits their structure, composed of packages of lepispheres arranged as grids that, depending on the orientation and how the light hits and the size of the spheres makes areas appear with different colors: red, orange, yellow, green...