Opals are hydrated silica and they are believed to be formed when molten silica finds its way into cracks and crevices in sandstone or other porous stone, and then cools and hardens. These mysteriously alluring gemstones have a unique distinction in the way they shine with every color in the spectrum. This characteristic is a result of the structural formation of the stone and the fact that they also contain between 3% and 20% water which enhances light refraction even further.
Some opal is clear, but most feature a stunning blend of translucent colors, mixed and swirled in a gorgeous fashion. Opals were relatively rare until they were found in large deposits in Australia in the mid-19th century. The land down under is now the source of more than 95% of all opal production in the world. It is no surprise, then, that opals are the gemstone of Australia, in addition to being the October gemstone. To bring out the beauty of the individual piece, opal is often cut or ground into round or oval cabochons, softly domed and often backed with a darker material, causing the splendor of the tones and shades to be more highly defined.
Grading an Opal
Opals are graded differently than gemstones like diamond or sapphire. Opals are primarily judged on the depth, brilliance, and richness of their coloration. Light passing into or through an opal produces an effect gemologist term “play of color.” The more colors that are included in a specific stone's play of color, and the more intense and vibrant those hues and tones are, the more valuable the stone will be considered. Beyond this, several additional factors are judged. Generally, the darker the stone’s natural background, the higher the grade given to the stone. Black and brown backgrounds are preferred. From there, shades range from gray to white or nearly clear.
Additionally, the breadth of the play of color across the surface is important. Brilliant color splashed over a larger percentage of the stone will increase its value. The transparency of the stone may enhance or detract from its value. Stones in which color can be seen to a greater depth are more prized than stones with shallow or milky color. It doesn’t take a gem expert to look at opals and see the wonderful effect these qualities produce. When you shop for stones their value will jump out at you with warm vibrancy that is undeniable.
Opals deserve a little extra attention when it is time to choose a mounting. A ring mounting for a beloved Opal should protect the stone from abrasion and hard blows to insure that it is enjoyed for many many years. If it should become hazy or abraded, chances are it can be restored to it's former glory with a simple polishing from a qualified lapidary.