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Black Opal Stones: Origin, Formation, Value & More About This Rare Gemstone

The Black Opal: The Mother Of All Gemstones

Black opals are rare gemstones with a personality entirely its own. It was Shakespeare who gave black opals their moniker, “The Mother of All Gemstones,” but it doesn’t take a gemologist to agree that the name fits. With their rainbow array of colors, blooming in fire-like patterns, they are in their own class for beauty and make unique engagement rings and fine jewelry. However, since they have become on trend, it can be difficult to know if you are buying a quality stone. Due to their unique nature, opals have a grading system all their own…

The Origins Of Black Opals: Where They Are From, How They Form

A solid black opal from Lightning Ridge, Australia with blue & green surrounding a red & yellow center.

Black opals are exceptionally rare in that they are known to form in only one place: Australia. In fact, most of the opals found on the continent are from the town of Lightning Ridge. To put this into perspective, Vatican City has a population of 1,000 and Lightning Ridge has just over double that. This means that these gems form on a single pinpoint on the entire planet. While Australia makes up 90% of the world’s opal market, mining these gemstones ethically and responsibly is extremely important due to their rarity. Once they’re gone, they’re gone from the Earth for thousands of years.

It’s the very nature of Australia that causes black opals to form. Scientifically speaking, they are made from a solution of silicon dioxide and water. Water carries silica through the earth, depositing it in cracks and openings in the crust. The water evaporates, but the chemical deposit is left behind. Add pressure to years and years of this process and eventually an opal takes shape.

These gems are made even more rare by their elusiveness even to mining experts. There are no veins of the gems, nothing to give miners a best bet clue as to where to look. All a person can do is dig and hope for the best.

How Do Black Opals Get Their Color?

Black opals are actually not black. They have a natural backing to them called “potch” that gives them their dark body color. Against this backdrop, all the colors of the rainbow can dance in stunning patterns. Other gemstones get their color due to specific elements present at the time of formation. For example, a diamond will only turn blue if Boron is present. So how does a black opal have so many vibrant colors at once?

Of all gemstones, opals are the true masters of light diffraction. This is because their main ingredient silica is the same one as in glass. As mentioned above, when the water evaporates, it leaves behind a silica deposit. These deposits are spherical and it is their stacking— layer upon layer—that creates gaps between the spheres. When the light passes through the spheres and their gaps, it splits like a rainbow from a prism. The result is the aurora or even peacock-like patterns of an opal’s many colors.

How Are Black Opals Graded?

Generally speaking, black opals are the most valuable variety of opals on the market. They are the golden South Sea pearl to all others. Aside from that key point, there are three points that gemologists take into consideration when grading:

1. Brilliance

2. Transparency

3. Pattern

What Is Opal Brilliance?

Brilliance in opals is how bright and clear the colors appear when the gem is face up. Are they crisp and vivid? Or are they dull and muddled? Experts will grade opals as brilliant, bright, subdued or dull accordingly. Brilliance is so important that more colors on a dull stone will go for less at market than a bright opal with less color play.

What Is Opal Transparency?

ust to be crystal clear, opal transparency is just that: translucent enough that a text can be read through the stone if it is placed on a page with direct light. This means that opals can range from transparent (clear) to opaque (cloudy). In fact, if an opal is more or less transparent it will be given the title “crystal,” while those that have cloudiness to them are translucent or “semi-crystal.” The more transparent an opal is, the easier it will be to see the many layers of colors.

Think of it like this:

Which water looks more beautiful?

Clear tropical waters with many colors of blue & green. Rocks visible beneath the surf.
Opaque ocean water with only greens & yellows visible on the tops of waves.

The one on the left has greater transparency, allowing a person to see the different colors and play of light beneath the surface. The one on the right is darker, cloudier, with only surface colors visible.

Fun Fact: Opals have water! What makes Australia’s opals more durable is that they have less water. Other’s can actually dry out over time and cause the stones to lose their durability.

What Are Opal Color Patterns?

Opals aren’t always a Jackson Pollock of colors. Sometimes they take on recognizable patterns, some of which are more rare and valuable than others. These can range from excellent to good. Those that fall under the “excellent” category will fetch a higher price than those with a “good” pattern.

Two Examples of Excellent Grade Patterns Are:

Blue & red harlequin black opal.

Harlequin: These consist of repeating color patterns of diamonds or elongated squares.

A black opal with bright yellow Chinese writing markings.

Chinese Writing: This is a curious opal pattern in which bright and bold lines of color overlap to resemble Chinese calligraphy.

Two Examples of Good Patterns Are:

A black opal with pin fire pattern.

Pinfire: These are characterized by small pinpoints of bright colors throughout the opal.

A black opal with a rolling flash pattern.

Rolling Flash: These opals have large bands of color that “roll” across the stone as it’s turned.

Myths And Legends About Opals

1. They are the October birthstone!

2. Depending on the culture, opals vary around the world as to whether they bring good or bad luck to the wearer.

3. Ancient Greeks believed that opals have such flashing colors because they are the tears of Zeus.

4. The Aborigines believed that opals were part of the “Rainbow Serpent” and feared them.

14k 5mm Opal Birthstone October Stud Earrings

If you are in the market for opals as a birthstone gift or simply as a unique piece of fine jewelry, the experts at Hamilton are happy to be of assistance. Come into one of our jewelry store locations and chat with us about your vision.

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