Opal is a hydrated silica. Due to its amorphous form, it is classified as a mineroid, rather than a crystalline mineral. When light enters the opal, the spherical shape of the silica causes the light to diffract, which results in the vibrant play of color that opal is famous for. The most common colors are white and green, but opal can also be nearly any color, with black opal being the most rare. Descriptions of the appearance of opal are fairly fabulous, as well, with terminology like “needle fire,” “church window,” “harlequin,” “lightning,” and “peacock” being used by opal experts. 95% of the world’s opal comes from Australia, with the tiny outback town of Coober Pedy being the major source.

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