Opals are known for their flashing display of rainbow colors or 'play-of-color.' There are two classes of opal, precious (which has the play-of-color) and common. Within these two classes of opal are the following 5 categories:
- white or light opal - show more diffuse colors against a white background and are the least expensive to purchase.
- black opal - dark black or gray body which shows play-of-colors optimally.
- fire opal - radiant orange and fire red in color. The most significant deposits come from Mexico, but are mined elsewhere. The Mayans and Aztecs called this stone quetzalitzlipyollitli, the 'stone of the bird of paradise.' Oval is the classical shape for a fire opal.
- boulder opal - play of color against a light to dark background.
- crystal or water opal - more transparent than black opal with a deep play of colors.
Roman scholar Pliny observed, “Some opali carry such a play within them that they equal the deepest and richest colors of painters. Others…simulate the flaming fire of burning sulphur and even the bright blaze of burning oil.”
For centuries, people have believed in the magical powers of opals. Some believe the stone help with depression and help find true love.
Opals and Tourmalines are the October birthstone.
The opal is between a 6 and a 6.5 on Mohs scale, but the fire opal is among the somewhat sensitive and requires a protective setting, especially when worn as a ring stone. It should be protected from extreme heat and cosmetics. Opals should be worn frequently because the gem will then receive the humidity it needs to ensure it does not become brittle.
The only way to clean opals is with warm, soapy water. Opals are often treated to protect the surface, and sometimes to improve the surface appearance. Do not polish opals, and exercise care when wearing to avoid contact with surface that may abrade the surface.