What is opal?
Opal is a hydrated amorphous form of silica, chemically SiO2·nH2O, best known for play of color caused by the diffraction of light through orderly silica spheres. Unlike crystalline quartz, opal has no regular crystal structure and can contain a notable amount of water. It is commonly cut as cabochons to showcase its moving flashes of green, blue, orange and red.

