The October birthstone opal has more variety of color and pattern than any other gemstone. Opal has always been considered somewhat mysterious and mercurial, probably because it embraces the colors of so many other precious and semiprecious stones.
The experts at the Gemological Institute of America (GIA). describe opal’s elusive qualities like this: “Fireworks. Jellyfish. Galaxies. Lightning. Opal’s shifting play of kaleidoscopic colors is unlike any other gem.”
The GIA tells us that the ancient Romans valued opal above all other gems; they thought it contained special powers precisely because it mimicked the colors of so many other gemstones.
The Bedouins believed that opals contained lightning and rained down on earth during thunderstorms.
It turns out they weren’t far off the mark.
How Opals Are Formed
When Australia’s mines began to produce commercial opals in the 1890s, the land down under quickly developed into the world’s primary source for what is today a popular October birthstone.
“Opal is a product of seasonal rains that drenched dry ground in regions such as Australia’s semi-desert ‘outback,’” say the GIA gemologists. “The showers soaked deep into ancient underground rock, carrying dissolved silica (a compound of silicon and oxygen).”
“During dry periods, much of the water evaporated, leaving solid deposits of silica in the cracks and between the layers of underground sedimentary rock. The silica deposits formed opal,” GIA reports.
Look for Play-of-Color
When evaluating an opal, or a piece of opal jewelry, it is important to note that opal is known for its “flashing” rainbow colors, commonly called “play-of-color.” There are two broad categories of opal: precious and common. Precious opal displays play-of-color, while common opal does not.
An Important 7.50-Carat Lightening Ridge Opal Diamond Cluster Ring
According to 1stDibs,com, opals like this one from the Lightening Ridge mine in Australia are known for their exceptional properties and play-of-color “…with intense red flashes and absolutely magical character. This opal is a rare beauty and a true testament to what nature can accomplish on her own!”
The opal is set in a platinum mounting surrounded by “a scalloped, diamond-studded border and finished with knife edge.” $60,000 on 1stDibs.com via Fourtane, Carmel-by-the-Sea
17.08-Carat Australian Black Opal Gem-Set Gold Ring
This exquisite ring, also available on 1stDibs, features an Australian black opal that presents a play-of-color ranging from green and blue to pink and red. The center stone is prong-set in an 18K white gold setting studded with precious gemstones including diamonds, blue and orange sapphires, and tsavorites.
These stones were specifically chosen to complement the hues exhibited in the opal itself. Opal weight: 8.04 carats; sapphires and tsavorites: 6.89 carats. $19,800 via Maurice Fine Jewelry.
Opening image courtesy of Meira T Jewelry / Pinterest.