Discover Australia's National Gemstone: The Fascinating Story Behind Opal

Opal is Australia's national gemstone and October's birthstone, famous for its shifting "play of colour" — flashes of rainbow hues that make every stone one of a kind. From its unique formation to its place in Australian culture, here's the story behind opal, the main types, and how to care for it. At Irosk Australia, our opal pieces are set in 925 sterling silver.

How Opal Forms

Opals formed under rare geological conditions. Millions of years ago, much of central Australia lay beneath an inland sea. As it retreated, silica-rich water seeped into cracks in the ground and slowly solidified into opal over a very long time — which is why opal is found in only a few places worldwide, with Australia the most prolific source.

Opal's signature "play of colour" comes from light diffracting through tiny silica spheres arranged in a regular pattern. The size and spacing of those spheres determine which colours appear, giving every stone its own ever-changing palette. Unusually, opal is a mineraloid rather than a true mineral — it has no crystalline structure and contains water, which makes it both special and a little delicate.

Opal in Australian Culture

Opal has deep roots in Australia. For Indigenous Australians, the stone features in Dreamtime stories — including a legend of a creator descending on a rainbow, where the ground sparkled into opal. European settlers found significant deposits in the late 1800s, and discoveries across Queensland, New South Wales and South Australia cemented Australia's reputation as the world's leading opal source.

Types of Opal

• Black opal: The most valued, with a dark body tone that makes its colours flash dramatically. Famously from Lightning Ridge, NSW.
• White opal: A milky, light body tone with soft to vivid colours, mainly from Coober Pedy and other South Australian fields.
• Boulder opal: Forms in thin seams within ironstone, creating striking natural contrast. Mostly from Queensland.

Caring for Your Opal

Opal's water content makes it more delicate than many gems, so a little care goes a long way:

• Avoid sudden temperature changes and very dry environments, which can cause crazing.
• Clean gently with a soft, damp cloth — avoid harsh chemicals and ultrasonic cleaners.
• Store in a padded box or soft pouch, and remove opal jewellery for swimming, gardening or sport.

Opal Myths and Facts

One persistent myth is that opal is "bad luck" — a superstition traced to a 19th-century novel with no factual basis. In fact, many cultures see opal as a symbol of good fortune. And a happy fact: opal is the official birthstone for October, which makes it a lovely birthday gift.

Explore our October Birthstone collection and Opal Jewellery range, including rings, necklaces, earrings and bracelets.

Frequently Asked Questions

Why is opal Australia's national gemstone?
Australia produces the vast majority of the world's opal and has deep cultural ties to the stone, so it was named the national gemstone.

What month is opal the birthstone for?
Opal is the birthstone for October.

How do I care for opal jewellery?
Avoid sudden temperature changes, clean gently with a soft damp cloth, store it padded and separate, and remove it for swimming, gardening or sport.

Written by the Irosk team. We handcraft birthstone and gemstone jewellery in 925 sterling silver for customers across Australia.