OPAL: The October Birthstone | Boca Raton, FL
The Birthstone of October
"The opal resembles a fraction of the rainbow softened by a milky cloud." - Charles Blanc
The October birthstone’s dramatic play-of-color has inspired writers to compare it to fireworks, galaxies and volcanoes. The Bedouins once believed that opal held lightning and fell from the sky during thunderstorms. The Ancient Greeks thought that opals bestowed the gift of protection from disease. The Europeans long maintained opal to be a symbol of purity and truth. Hundreds of years ago, opal was believed to embody the virtues and powers of all colored stones. And because opal has the colors of other gems, the Romans thought it was the most precious and powerful of all.
How Opal is Formed
TYPES OF OPAL
- White or light opal: Translucent to semitranslucent, with play-of-color against a white or light gray background color, called bodycolor.
- Black opal: Translucent to opaque, with play-of-color against a black or other dark background.
- Fire opal: Transparent to translucent, with brown, yellow, orange, or red bodycolor. This material—which often doesn’t show play-of-color—is also known as “Mexican opal.”
- Boulder opal: Translucent to opaque, with play-of-color against a light to dark background. Fragments of the surrounding rock, called matrix, become part of the finished gem.
- Crystal or water opal: Transparent to semitransparent, with a clear background. This type shows exceptional play-of-color.
Opal Quality Factors
- Color—Background color and play-of-color
- Pattern—Arrangement of play-of-color
- Clarity—Transparency and quantity of inclusions
- COLOR. Opal hues can range across the spectrum. An opal might display a single color, two or three colors, or all the colors of the rainbow. Opal displays background color in addition to play-of-color. Background color—also called bodycolor—is caused by the suspension of tiny impurities within opal’s silica spheres. Play-of-color might be the most spectacular aspect of an opal’s appearance. No matter the color or combination of colors, play-of-color must be vivid to command a high rating.
- PATTERN. Pattern describes the arrangement of an opal’s play-of-color. Like the shapes you see in the clouds, play-of-color takes many forms.
Common terms for play-of-color patterns include:
- Pinfire or pinpoint: Small, closely set patches of color
- Harlequin or mosaic: Broad, angular, closely set patches of color
- Flame: Sweeping reddish bands or streaks that shoot across the stone
- Peacock: Mainly blue and green
In general, connoisseurs prefer large, closely arranged patches of color over tiny, scattered dots. As with any play-of-color, no matter what the pattern, colors must be bright for the stone to be valuable.
- CLARITY & TRANSPARENCY. With an opal, clarity is its degree of transparency and freedom from inclusions. An opal’s clarity can range all the way from completely transparent to opaque. Experts prize different levels of clarity for different opal types.
- CUT. The cutter considers an opal’s color, pattern, and clarity when planning the finished gem. As with many top-quality colored stones, exceptional opals might not be cut to standard sizes and shapes.
- CARAT WEIGHT. Opals come in a wide range of sizes and carat weights. Opal has relatively low density compared to many other gemstones so even larger sizes can be comfortable to wear. Common sizes for many of the opal cabochons set in jewelry are 6×4, 7×5, and 8×6 mm.