Opal (o’ pel)
Opal is mineral of hydrated silica SiO2 nH2O with a specific gravity of 2.5 and has a hardness of 5-6.5 on the mohs scale. An amorphous usually iridescent mineral that can be almost any color. Found in igneous rocks and around hot springs. Australia is where some of the best opals come from with Ethiopia and Mexico coming second and third. Ninety percent of precious opals come from Australia.
Types of Opal are precious opal, common opal and fire opal. Precious opals display a “play of colors”. The play of colors comes from the submicroscopic spheres stacked in a grid like pattern. Like a box of ping pong balls. They are sized from .1 microns, violet color and to .2 microns, red color. Light waves travel between the sphere diffracting or bending. When light waves bend they are broken up into the colors of the rainbow. Thus giving it the “play of colors”, also called spectral colors. Precious opal is very rare and found in a limited numbers of locations. Common opal shows no signs of a play of colors but some specimens can still be attractive with many colors and luster. Fire opal is colorful and has a bright fire like background of yellow, orange or red. It may or may not have a play of colors.
Opal has patterns in the “play of colors” known as Harlequin opal that are like patches of color either rectular or diamond shapes. Pin fire opal has pinpoints of fire throughout the stone. Cats eye opal has a fire that is optical effect similar cats eye.
Opals are sometimes constructed of multiple layers known as doublets or triplicates. Doublets are the stone and base of black material glued together and triplicates are the stone, base and a clear material on top for protection.
Opals are easy to work but you need to know how to expose the fire in the stone. Once you learn how to cut and polish these they can be very beautiful. I enjoy working with opals because each one can be very different from one another. Opals are the birthstone for October and there is superstition that only people born in October should where this stone.
Jay Paulson of Glendora Gems