Opals: Nature's Most Enchanting Gemstone

Ancient legends, hidden rainbows, and the extraordinary science behind a gemstone unlike any other.

There are gemstones that sparkle, gemstones that glow, and then there are opals.

Look into an opal, and you may discover flashes of color that seem almost impossible. A ribbon of electric blue, a flicker of emerald green, or a brilliant burst of red and orange. Some resemble tiny galaxies, while others seem to hold the colors of a sunset or the northern lights.

Move the gemstone ever so slightly, and the colors may shift, disappear, or reveal something entirely new.

It is little wonder that opals have inspired centuries of legends and superstition. Before anyone understood the science behind their extraordinary appearance, these gemstones seemed to possess something otherworldly.

Yet perhaps the most fascinating thing about opals is that their beauty requires no magic at all. Nature has already done something remarkable.

A Rainbow Millions of Years in the Making

Opals begin their journey beneath the Earth's surface, where water carrying dissolved silica moves through cracks and cavities in rock.

Under suitable geological conditions, silica becomes deposited in these spaces, eventually forming opal. This process can take place over vast periods of geological time.

Unlike diamonds, sapphires, and rubies, opal does not have a regularly ordered crystalline structure. Instead, it is a mineraloid composed of hydrated silica, meaning its structure contains water.

But what gives precious opal its spectacular colors?

The secret lies in microscopic spheres of silica.

In precious opal, these spheres are arranged in sufficiently regular patterns to interact with visible light. As light travels through the gemstone, it undergoes diffraction and interference, producing the shifting colors known as play-of-color.

The size and arrangement of the spheres influence the colors we see. Smaller spheres are associated with shorter wavelengths of light, such as blue and violet, while larger spheres can produce longer wavelengths, including orange and red.

And here is something particularly fascinating: the colors are not produced by pigments trapped inside the stone. They result from the way light interacts with its microscopic structure.

An entire rainbow, created by structures far smaller than the human eye can see.

  

When Opals Fell from the Heavens

Long before modern gemology explained the mysteries of opal, ancient civilizations had their own ideas about its origins.

According to traditions associated with the Bedouins, opals contained lightning and fell from the sky during thunderstorms. The ancient Greeks believed the stones could bestow the gift of prophecy and offer protection against disease.

The Romans held opals in particularly high regard.

The Roman naturalist Pliny the Elder admired opals for displaying the colors of several precious gemstones within a single stone. He described their resemblance to the red of ruby, the green of emerald, and the blue of sapphire.

In ancient Rome, opal was associated with love and hope.

For centuries, opals enjoyed a reputation as gemstones of good fortune. Their later association with bad luck is surprisingly recent.

Much of that superstition can be traced to Sir Walter Scott's 1829 novel Anne of Geierstein, in which an opal plays a dramatic role. The story helped popularize an unfortunate reputation that had little connection to the gemstone's earlier history.

It seems a fictional story managed to cast a shadow over a gemstone that had been admired for thousands of years.

Today, opal is one of October's traditional birthstones, although we believe a gemstone this beautiful hardly needs a birthday invitation.

Not All Opals Are Created Alike

One of the most delightful things about opals is their extraordinary variety. While some are famous for their dramatic flashes of color, others possess a softer, almost dreamlike beauty.

White Opal

White opals have a white or light body tone, often providing a delicate background for flashes of pink, green, blue, or orange. Their luminous appearance can be especially beautiful in antique jewelry.

Black Opal

Black opals have a dark body tone that provides striking contrast against their play-of-color. Fine black opals can display exceptionally vivid colors and are among the most valuable varieties.

Boulder Opal

Found within host rock, often ironstone, boulder opal is commonly cut with a portion of its natural matrix remaining attached. The contrast between the colorful opal and the surrounding rock gives each piece a distinctive character.

Crystal Opal

Crystal opal is transparent to semitransparent and may display brilliant play-of-color. Its clarity can give the impression that the colors are suspended within the stone.

Fire Opal

Fire opal is recognized for its warm yellow, orange, or red body color. Despite its name, fire opal does not necessarily display play-of-color. Some transparent examples are faceted, unlike the rounded cabochons commonly associated with precious opal.

Common Opal

Not all opals display a rainbow. Common opal lacks play-of-color but can occur in beautiful shades of pink, blue, green, yellow, and other colors.

Each variety has its own appeal, and no two individual opals have precisely the same appearance.

The Opal That Changes When It Gets Wet

As though shifting rainbows were not fascinating enough, certain opals have another remarkable characteristic: they can absorb water and temporarily change their appearance.

These are known as hydrophane opals.

Hydrophane opals have a porous internal structure that allows them to absorb liquids. As water enters the gemstone, it changes how light travels through the material.

The result can be quite surprising.

An opal that appears milky or opaque when dry may become noticeably more transparent after absorbing water. Its body color and apparent play-of-color may change as well, sometimes quite dramatically.

As the absorbed water gradually evaporates, the gemstone will often return to its original appearance, although the process and outcome depend on the individual stone.

Ethiopia is an important source of hydrophane opal, particularly from the Wollo region.

At Gilded Roach, we have a hydrophane opal that provides a fascinating opportunity to see this phenomenon firsthand. Our photographs show how the appearance of the same gemstone changes when dry and after exposure to water.

It is a wonderful example of how even something as familiar as water can reveal an unexpected characteristic of a gemstone.

Our hydrophane opal showing the change in appearance that occurs when the gemstone absorbs water. The difference is caused by a change in how light travels through the porous material.

An important note: Although hydrophane opals can absorb water, deliberately soaking them is not recommended as a routine practice. Some contain internal fractures that may worsen with exposure to moisture, and certain liquids can cause unwanted discoloration. The photographs are intended to demonstrate a gemological property, not a recommended method of caring for opal jewelry.

Where Do These Extraordinary Gemstones Come From?

Australia is the world's principal source of precious opal and is home to several famous opal-producing regions.

Lightning Ridge, in New South Wales, is especially renowned for its black opals. Coober Pedy, in South Australia, is celebrated for its white and light opals, while Queensland is well known for boulder opal.

Opals are also found in Ethiopia, Mexico, Brazil, Honduras, and the United States, among other locations.

Each geological environment contributes to the remarkable diversity of opal.

But perhaps one of the most astonishing discoveries involving opals is that they can sometimes preserve traces of prehistoric life.

In Australia, scientists have discovered opalized fossils, including shells, plants, and even ancient vertebrate remains. These fossils formed when silica-rich material replaced or filled parts of ancient organisms, preserving their structures in opal.

Imagine discovering a fossil from the age of the dinosaurs, preserved in a material capable of displaying flashes of rainbow color.

Few gemstones have a geological history quite so extraordinary.

What Makes One Opal More Valuable Than Another?

While diamonds are often evaluated using the familiar Four Cs, opals have their own important quality factors.

One of the most significant is the brightness of their play-of-color.

An opal displaying strong, vivid flashes of color will generally be more desirable than one whose colors appear faint or subdued.

The range of colors also influences value. Opals displaying several brilliant colors, especially including red, can be particularly prized.

Pattern matters, too.

The arrangement of an opal's play-of-color may be described with names such as pinfire, broad flash, ribbon, flame, or harlequin. These names refer to the different ways colors appear across the gemstone.

Body tone, transparency, size, cutting quality, and condition also contribute to an opal's value.

But beauty is not always something that can be neatly measured.

One person may fall in love with an opal displaying fiery reds and oranges, while another may prefer the quiet movement of blue and green across a pale background.

There is something rather lovely about a gemstone that offers so many different expressions of beauty.

Opals in Antique and Vintage Jewelry

Opals have been admired in jewelry for centuries, but they hold a particularly romantic place in Victorian and Edwardian designs.

During the nineteenth century, opals appeared in rings, brooches, pendants, and other ornaments. Their shifting colors created a beautiful contrast with yellow gold and complemented the decorative designs of the period.

The opal's characteristic play-of-color also made it an appealing choice for jewelry that celebrated nature, individuality, and unusual gemstones.

During the Edwardian era, opals continued to appear in delicate settings, sometimes accompanied by diamonds or intricate metalwork.

Many antique opals were cut into smooth, rounded cabochons rather than faceted shapes. This style of cutting can beautifully display an opal's play-of-color while retaining the character of the natural gemstone.

For collectors of antique and vintage jewelry, opals offer something especially appealing. Their beauty is not limited to the stone itself but extends to the craftsmanship, design, and history of the piece in which they are set.

An opal ring created more than a century ago may have passed through generations, all while continuing to reveal the same remarkable colors that first captivated its original owner.

There is a quiet sense of wonder in that thought.

Caring for Your Opal Jewelry

Opals may look almost otherworldly, but they are very much natural gemstones, and understanding their properties is important to preserving their beauty.

With a hardness of approximately 5 to 6.5 on the Mohs scale, opals are softer than diamonds, rubies, and sapphires. They can be scratched, chipped, or damaged by impact.

Opals also contain water within their structure, and some are sensitive to high temperatures, abrupt temperature changes, or excessively dry conditions.

To help protect your opal jewelry, remove it before strenuous activities, gardening, household cleaning, or any situation where it may be struck against a hard surface.

Avoid ultrasonic cleaners, steam cleaning, and harsh chemicals.

For solid, non-hydrophane opals, gentle cleaning with a soft cloth and a little mild soapy water is generally appropriate. Hydrophane opals, opal doublets, and triplets may require different care because their structures or assembled layers can be affected by moisture.

If you are uncertain about the type of opal you own, a qualified jeweler can help you determine the safest cleaning method.

Thoughtful care allows these extraordinary gemstones to remain beautiful for generations.

A Little Wonder Beneath the Surface

Perhaps the most captivating thing about opals is that they never seem to reveal everything at once.

Tilt one toward the light, and a flash of brilliant green may suddenly appear. Turn it again, and a ribbon of blue gives way to fiery orange. What looked like an ordinary pale stone a moment earlier becomes a tiny landscape of changing color.

Their formation is geological, their colors are optical, and their history is woven through centuries of human imagination.

Even knowing the science does little to diminish the wonder.

At Gilded Roach, we are drawn to jewelry with character, history, and unexpected beauty. Opals capture all three. Whether set in an antique gold ring or admired as a natural specimen, each one offers something entirely its own.

And perhaps that is the real enchantment of opal.

Even after you understand how it works, it still has the power to surprise you.

Beauty found in the unexpected.