A Jeweller’s Guide to Opal: Identification Tips and Jewellery Making Advice

Step into the shimmering world of opals!

Beloved for their unique play-of-colour and dreamy, iridescent glow, opals are unlike any other gemstone. Whether it’s a pastel-hued cabochon or a fiery black opal that dances with every colour of the rainbow, these gems have long captivated jewellers and collectors alike.

Here’s everything you need to know about working with opal in your jewellery designs.

Basic Identification Information

Name & Synonyms:
Opal.
I've included a list of trade names at the end of this gem profile.

Species:
Opal

Colour Range:
White, black, grey, blue, green, orange, red, pink, brown, yellow, colourless.
Many opals show “play-of-colour” – a rainbow-like optical effect.

Refractive Index:
1.370 – 1.470

Birefringence:
None (singly refractive)

Optical Sign:
N/A

Pleochroism:
None

Specific Gravity:
1.25 – 2.23

Fluorescence:
Variable – may be inert or strong fluoresce white, green, or yellow

Lustre:
Subvitreous to waxy or resinous

Clarity:
Usually translucent to opaque, though crystal opals can be transparent

Gems Often Mistaken for Opal:
Opalite (glass), synthetic opal

Mohs Hardness:
5 to 6.5

Wearability:
Fair. 

Birthstone:
October (alongside tourmaline)

Spotting Synthetic (lab-grown) Opal

Synthetic opal can be beautiful and convincing, but if you’re aiming to use natural gems in your designs, it’s essential to know the visual clues that give lab-created opals away. Here’s what to look out for:

“Chicken Wire” or “Lizard Skin” Pattern
One of the most distinctive giveaways of synthetic opal is its internal pattern. Many lab-grown opals display a uniform, grid-like or 'snakeskin' texture within the play-of-colour, often described as looking like chicken wire. This effect forms because the colour patches in synthetic opals are arranged in a repeating, often hexagonal or columnar pattern, unlike the organic, random flashes in natural opal.

Play-of-Colour from Every Angle
Natural opal often displays directional play-of-colour, meaning it appears most vivid from certain angles and more subdued from others. Synthetic opals, especially the modern ones, tend to show a bright, even play-of-colour in all directions.

Too Perfect to Be True?
If the colour play is exceptionally bright, saturated, and uniform across the entire surface, be cautious. Many natural opals have areas of potch (non-colourful opal) or uneven colour distribution. Synthetic stones often lack these natural “imperfections.”

Visible Columnar Structure in Side View
In some lab-grown opals (especially older types like Gilson opal), you might spot a columnar or stacked structure when viewed from the side, particularly in thicker cabochons. These vertical 'growth lines' don’t occur in natural opal.

Common Treatments

Many opals on the market are treated to enhance appearance. Common treatments include:

Sugar-acid treatment or smoke treatment to darken the body colour and improve play-of-colour.

Resin or plastic impregnation to improve durability in porous opals.

Doublets and triplets: Thin slices of opal are layered with backing (doublets) and sometimes a clear quartz or glass cap (triplets).

These treatments can affect care and durability, so always verify what kind of opal you’re working with.

Durability Considerations

Opal is a relatively soft and delicate stone. It can be scratched or chipped easily, and many opals contain significant water content, making them sensitive to changes in humidity and temperature.

• Avoid sudden temperature changes, prolonged exposure to water (especially for doublets/triplets), and harsh chemicals.
• Store away from harder gems to prevent scratching.

When designing jewellery with opals, it's best to use protective settings such as bezels or deep prongs to help shield the stone from damage. Avoid tension settings or open designs that leave the opal too exposed, as these increase the risk of chipping or cracking.

It's also wise to consider creating opal rings intended for occasional wear, such as cocktail-style pieces, rather than for everyday use.

Jeweller’s Setting Tips

Because opal is both soft and brittle, it should be treated with care during setting. Here are some tips:

• Use minimal pressure when securing the stone to avoid cracking.
• For natural solid opals, a low bezel setting offers both security and elegance.
• If you’re working with doublets or triplets, be cautious with heat and moisture as these constructions can fall apart.
• Avoid ultrasonic cleaners or any polishing near the stone once it’s set.

If adjustments are needed post-setting, always remove the stone before soldering.

Care Instructions

Cleaning:
Use a soft cloth that's been dampened with warm soapy water (use a mild soap).
Avoid ultrasonic and steam cleaners.  

Storage:
Store in a soft pouch or individual compartment to prevent scratches. Some jewellers recommend storing opals in a slightly humid environment (like a sealed bag with a damp cloth nearby) to prevent dehydration, especially in arid climates.

Daily Wear:
Best for earrings, brooches, and pendants. Rings should be reserved for special occasions unless protected by a robust setting and worn mindfully.

Aesthetic & Design Insights

Opals are all about personality. Each one is unique, and their shifting colours can change dramatically under different lighting.

Metal Pairings:

Yellow or rose gold enhances warm body tones and fiery flashes.
White gold or silver creates contrast with darker opals and makes cool hues pop.

Companion Stones:

Diamonds, white sapphires, or moissanite can frame opals beautifully without overpowering them.
For a dreamy, mystical palette, consider pairing with moonstone or aquamarine.

Design Styles:

Opals shine in organic, nature-inspired jewellery and statement pieces. They also lend themselves well to bohemian and vintage styles where the unique character of each stone is a feature.

Avoid overly industrial or rigid designs, opals look their best when given space to shimmer.

Market & Ethical Notes

Opals are mined in several countries, most famously:

Australia – known for high-quality black, white, and boulder opals.

Ethiopia – produces vivid crystal opals, though many are hydrophane (Highly porous opal that can absorb water and temporarily change appearance or transparency).

Mexico – home of fire opals, often orange-red and transparent, sometimes with play-of-colour.

Australian opals are generally considered more stable and less prone to treatment. Ethiopian opals, while beautiful, require more care and are often treated to improve colour stability.

As always, source from reputable suppliers who disclose treatments and origin. Ask for specifics, especially when purchasing for high-value designs.

Symbolic & Spiritual Meanings

Opal has long been associated with creativity, intuition, and inspiration. Its ever-shifting play-of-colour symbolises change, transformation, and inner fire.

Because it’s such a unique and personal stone, many believe the right opal finds you, not the other way around.

Etymology

The name “opal” comes from the Latin opalus, thought to be adapted from the Sanskrit upala, meaning “precious stone.” Fittingly mysterious for such a unique gem.

Varieties and Trade Names

There are other types of opal on the market, such as pink opal or dendritic opal, but I’ve kept this list focused on varieties of precious opal (opal that can show play-of-colour), rather than covering the full range of common opals.

White Opal – Light body tone with play-of-colour

Black Opal – Dark body tone; prized for vibrant colour flashes

Boulder Opal – Opal formed within ironstone matrix, usually from Queensland
-Yowah Nuts – Ironstone nodules from Yowah, Queensland that may contain pockets or veins of opal. Often cut open to reveal vibrant colour play inside. These are a type of bolder opal.

Crystal Opal – Transparent to translucent with strong play-of-colour

Fire Opal – Orange, red or yellow; may or may not show play-of-colour

Honey Opal – A transparent to translucent opal with a warm golden-yellow or amber tone. May or may not show play of colour.

Jelly Opal – A translucent to semi-transparent opal with a gelatinous, glowing appearance. Often has a soft play of colour and a smooth, watery look.

Matrix Opal – A type of opal where the play-of-colour is naturally distributed within the host rock, often creating a speckled or web-like effect.
-Andamooka Matrix Opal – A specific type of porous matrix opal (typically from Andamooka) treated with sugar and acid to darken the body tone and highlight colour play.
-Painted Lady – A type of matrix opal from Andamooka, South Australia, named for its vivid, painterly patches of colour spread across a tan matrix.

Opalized Fossils – Fossilised bones, shells, or wood that have been replaced or filled with opal. These can include dinosaur bones and ancient sea life, often with striking colour flashes.

Potch – Opal with no play-of-colour, can be lovely in pastel shades, sometimes called common opal.

Doublet – Thin slice of opal on a backing layer. Sometimes potch is used as the backing layer so the doubled is entirely made of opal.

Triplet – Doublet with a clear cap (usually quartz or glass)