Beyond Precious Opal
Discovering the Many Faces of the Opal Family
Curator's Notes
Classification: Hydrated Silica (Opal)
Composition: SiO₂·nH₂O
Structure: Amorphous (Non-crystalline)
Mohs Hardness: 5.5-6.5
Notable Localities: Australia, Ethiopia, Mexico, Brazil, Honduras, United States
Known For: Play-of-color, hydrophane varieties, fluorescence in hyalite opal
For many people, the word opal calls to mind brilliant flashes of blue, green, and fiery orange dancing beneath the surface of a gemstone. Those remarkable colors, known as play-of-color, have captivated people for thousands of years.
Yet precious opal is only one member of a surprisingly diverse family.
Some opals glow an electric green beneath ultraviolet light. Others are completely transparent. Some contain brilliant flashes of color suspended within crystal-clear stone, while others display warm honey tones with no play-of-color at all. A few can even absorb water and temporarily change their appearance.
The more one learns about opals, the more extraordinary they become.
What Is Opal?
Unlike most gemstones, opal is not a crystal.
Instead, it is composed of tiny spheres of hydrated silica arranged in microscopic patterns. When those spheres are exceptionally uniform, they scatter light into brilliant flashes of color that seem to move as the stone turns.
This phenomenon is known as play-of-color, and it is unique to precious opal.
Because opal contains water as part of its natural structure, it is also one of the more delicate gemstones commonly used in jewelry.
Understanding the Mohs Hardness Scale
If you've ever researched gemstones, you've probably encountered something called the Mohs Hardness Scale.
Developed in 1812 by German mineralogist Friedrich Mohs, the scale measures a mineral's resistance to scratching on a scale from 1 to 10.
Imagine carrying a handful of loose gemstones in your pocket.
A quartz crystal (Mohs 7) could scratch an opal (Mohs 6), but it couldn't scratch a sapphire (Mohs 9). That simple relationship is all the Mohs scale tells us.
It does not tell us whether a gemstone is likely to chip, crack, or survive being dropped.
Jewelers also consider a gemstone's toughness, which describes how well it resists breaking, and its stability, or how well it withstands heat, chemicals, sunlight, and changes in humidity. Together, these characteristics help determine where a gemstone will be happiest, whether that's in a necklace, a pair of earrings, or a ring designed for everyday wear.
Precious Opal
Precious opal is the variety most people recognize.
Its famous flashes of color appear because of incredibly uniform silica spheres arranged beneath the surface, creating a natural diffraction of light.
Every precious opal displays its own unique pattern. Some resemble tiny pinpoints of color, while others reveal broad flashes, rolling ribbons, or mosaic-like patches that shift with every movement.
No two are ever quite alike.
Fire Opal
Despite its name, fire opal is not prized primarily for play-of-color.
Instead, it is admired for its vibrant body color, which ranges from sunny yellow to brilliant orange and deep red. Many fire opals are beautifully transparent and contain little or no rainbow flash at all.
Mexico is especially famous for producing spectacular fire opals whose warm colors seem to glow from within.
Fire Agate
Fire agate is one of nature's hidden treasures.
Unlike precious opal, its fiery flashes are created by microscopic layers of iron oxide rather than silica spheres. The result is an almost metallic display of reds, oranges, greens, and golds that appears to burn beneath the surface.
Because it forms within layers of chalcedony, fire agate is generally tougher than many other members of the opal family.
Jelly Opal
Jelly opal earns its delightful name from its remarkable transparency.
Its crystal-clear body creates the impression that flashes of color are suspended inside a droplet of water. When light passes through the stone, the effect can be almost ethereal.
Yellow Opal
Not every opal displays play-of-color.
Yellow opal is appreciated instead for its warm, buttery hues, ranging from soft cream to rich honey gold. Its beauty lies in its quiet glow rather than dramatic flashes of rainbow color.
Sometimes, the gentlest gemstones speak the softest.
Hyalite Opal
Perhaps the most surprising member of the family, hyalite is nearly transparent.
At first glance, it may resemble a droplet of glass.
Under ultraviolet light, however, many specimens fluoresce a brilliant green due to trace amounts of naturally occurring uranium incorporated during their formation.
It is one of those wonderful reminders that nature is often stranger than fiction.
Hydrophane Opal
Some opals possess an extraordinary ability.
Known as hydrophane opals, they contain microscopic pores that allow water to enter the stone.
When this happens, the opal may temporarily become more transparent or lose much of its play-of-color before gradually returning to its original appearance as it dries.
Many Ethiopian opals display this fascinating characteristic.
Because repeated soaking may introduce dirt or oils into the stone over time, most jewelers recommend avoiding unnecessary exposure to water.
Jewelers have long known that many hydrophane opals have a habit of sticking ever so slightly to the tip of your tongue. Because they're naturally porous, they cling gently, while non-hydrophane opals generally do not.
If you're curious whether your own opals are hydrophane, gently touch your opal to the tip of your tongue. If it sticks ever so slightly, it's likely hydrophane. If it doesn't, it probably isn't.
It's hardly the most scientific test, and it's certainly not the last word on identification, but it's a wonderfully memorable (and fun!) reminder that some gemstones still have a few surprises waiting to be discovered.
Smoked Opals
Some opals have been intentionally darkened through a treatment known as smoking.
The darker body color enhances the visibility of the stone's colorful flashes, often creating a dramatic appearance.
Smoked opals are genuine opals.
The treatment simply enhances their appearance and should always be disclosed when sold. Purchasing from knowledgeable jewelers helps ensure you understand exactly what you're bringing home.
Doublets and Triplets
Not every opal jewelry piece contains a solid opal.
Some are carefully assembled from multiple layers.
An opal doublet consists of a thin slice of precious opal permanently bonded to a darker backing, while a triplet adds a protective transparent cap, usually made of quartz or glass.
These techniques allow more people to enjoy the beauty of precious opal while helping protect especially thin material.
Caring for Opal
Like many remarkable things in nature, opals reward thoughtful care.
Avoid sudden temperature changes, prolonged soaking, ultrasonic cleaners, harsh chemicals, and unnecessary impacts.
Clean your opal jewelry gently with a soft cloth and mild soap if needed, then dry it thoroughly before storing it separately from harder gemstones that could scratch its surface.
With a little care, an opal can remain beautiful for generations.
Artist's Reflections
One of the things I love most about opals is that they refuse to fit neatly into a single definition.
Some shimmer with impossible rainbows. Others glow beneath ultraviolet light. Some appear almost transparent, while others carry warm colors with quiet elegance. They remind us that beauty often reveals itself in many different forms.
As a jeweler, I also appreciate what opals teach us about respect.
Not every gemstone is meant to endure the same journey. Some thrive in rings worn every day. Others are happiest resting safely against the collarbone or dancing gently from a pair of earrings.
Understanding those differences isn't about limiting creativity.
It's about listening.
A jeweler's role isn't to force every gemstone into every design. It's to understand each material well enough to know where it will flourish.
With gratitude for your curiosity,
Rhiana
Artist & Founder, Larsen Jewelry
Continue Your Visit
Every remarkable material has a story to tell, and opals are no exception. From the fiery flashes of precious opal to the surprising glow of hyalite and the ever-changing nature of hydrophane opals, each variety offers its own glimpse into the extraordinary creativity of the natural world.
If you'd like to learn how to keep your opal jewelry looking its best for years to come, continue your visit in The Conservator's Notebook with Caring for Opals, where we'll explore thoughtful techniques for cleaning, storing, wearing, and preserving these remarkable gemstones with confidence.
Or, if you'd like to revisit the science behind one of nature's most captivating treasures, return to the Hall of Earth Sciences and Opal: The Stone That Captures Light, where we explore how opals form, why they shimmer with impossible color, and the remarkable journey that brought them from deep within the earth to the jeweler's bench.