Opal Basics 101: What is opal?

Imagine a gemstone that holds all the colours of the rainbow, shimmering in shifting patterns that dance with the light. A gem so unique that no two pieces are ever the same—each one as individual as a snowflake or a fingerprint. That gemstone is opal.

Whether you’re a gem enthusiast, jewellery lover, or simply curious about one of nature’s most captivating treasures, this guide will take you through the fascinating basics of opal gemstones — from how they form to what makes them so brilliantly colourful.

What exactly is opal?

Opal is one of the world’s most stunning and sought-after gemstones—prized not only for its ethereal beauty, but also for its unique internal structure that creates an optical wonder known as play-of-colour.

From a scientific perspective, opal is a mineraloid (not a mineral) composed primarily of silica (SiO₂·nH₂O)—the same base component as quartz, but with a notable twist: it contains water, typically between 3% and 10% in precious opals. This water content gives opal its glassy, delicate nature and is one of the reasons it forms in such a fascinating way.

How Is Opal Formed?

Most Australian opals — including black, crystal, and white opal — formed between 65 and 135 million years ago. These beautiful gems were born in ancient inland seas that once covered parts of Australia, particularly the vast underground water network known as the Great Artesian Basin.

Here’s how the process works:

1. Silica-rich water from ancient weathered sandstone seeps into underground cracks, voids, or cavities in rocks.

2. Over thousands — even millions — of years, the water evaporates, leaving behind a hardened gel composed of microscopic silica spheres.

3. These tiny spheres settle and form structured layers — and when aligned just right, they produce the colourful play-of-colour that opal is famous for.

Why is opal so colourful?

The answer lies in the silica spheres within the opal’s structure. In precious opal, these spheres are uniform in size and tightly packed in a grid-like pattern. As light hits the opal, it bends and diffracts through these layers—breaking into a spectrum of colours, like a prism.

• Larger spheres produce red hues — the rarest and most valuable colour.

• Medium spheres give off greens and blues.

• Smaller spheres create violets and indigos.

The spacing and alignment of the spheres determine both the intensity and range of colours you see. The more vivid and vibrant the colour, the more prized the opal.

What does ‘play-of-colour’ mean?

One of the most mesmerising aspects of opal is its play-of-colour—the magical movement of shifting colour across the gem’s surface (or face) as it’s tilted or turned in the light. No other gemstone offers this type of brilliance in such a wide array of hues.

Common opal patterns include:

• Harlequin – checkerboard flashes of colour

• Pinfire – tiny pinpoint flecks of light

• Rolling Flash – a band of colour that moves like a wave

• Chinese Writing – colour patterns resembling calligraphy

• Flower Garden – floral-like bursts of colour

• Mackerel Sky – cloudy or dappled sky-like patterns

Each pattern adds a layer of beauty and value, especially when paired with rich, bold colours.

Opal vs Other Gemstones

Unlike most gemstones, opal is not crystalline — it doesn’t have a rigid internal structure. This amorphous nature gives opal its fluid, dreamlike appearance but also means it requires a bit more care than harder stones like diamonds or sapphires. However, opal’s organic origins, dazzling colour play, and infinite uniqueness have made it one of the most treasured and meaningful gemstones throughout history.

What Are the Benefits and Meaning of Opal?

Throughout the ages, opal has been associated with inspiration, creativity, and emotional healing. It’s said to enhance intuition, balance emotions, and spark the imagination. Some believe the colour-changing properties of opal symbolise transformation and hope, making it a popular gemstone for those embracing personal growth or new beginnings.

How Can I Wear or Own an Opal?

Thanks to its versatility and breathtaking beauty, opal looks incredible in just about any form of jewellery:

• Opal rings – from bold statement pieces to elegant engagement rings

• Opal necklaces and pendants – showcasing the stone’s brilliance at your neckline

• Opal earrings – colourful yet refined, perfect for everyday or special occasions

• Opal bracelets – a vibrant touch to your wrist with character in every stone

At Black Star Opal, we offer a wide range of natural Australian opal jewellery, including black opals, crystal opals, boulder opals, and more. Each piece is handcrafted and ethically sourced to ensure exceptional quality and authenticity.

Why Choose Australian Opal?

Australia is the undisputed leader in the global opal market, producing over 90% of the world’s precious opals. Regions like Lightning Ridge, Coober Pedy, and Queensland’s boulder opal fields are known for producing opals with the most vivid colour and highest quality. Australian opals are also ethically mined and known for their durability and brilliance, making them highly desirable among collectors and jewellery lovers alike.

In conclusion, opal is far more than just a beautiful gemstone — it's a fascinating natural wonder shaped by time, water, and the Earth's unique geological processes. From its mesmerising play-of-colour to its remarkable variety of forms and patterns, opal continues to captivate gem lovers, scientists, and collectors alike. Whether you're drawn to its vibrant hues, intrigued by its ancient origins, or simply enchanted by its uniqueness, opal offers a brilliant glimpse into the magic and mystery of our planet’s deep history.

About the Author

Growing up on the opal fields of Lightning Ridge and working in her family’s opal business for much of her life, Black Star Opal founder Olivia Deskoski brings deep, first-hand knowledge and rare expertise to Australia’s opal industry. Her qualifications include gemmology and diamond technology studies with the Gemmological Association of Australia, a Master’s in Journalism, and extensive experience in e-commerce and marketing communications. In 2015, Olivia created the world’s first opal-themed light installation for Vivid Sydney and has helped raise $1 million for the new Australian Opal Centre at Lightning Ridge.