The October birthstone is opal, a gem that seems to hold a rainbow inside it. No two opals look quite the same, which is a big part of their charm. Opal is also softer than most gems, so it rewards a little knowledge and care. In this guide from Wanderlust Jewelry we look at what makes opal shimmer, the main types, the beliefs around it, and how to look after opal jewellery.
October birthstone: opal at a glance
- What it is: a gem formed from silica left behind in rock by evaporating water.
- Its signature: play-of-colour, flashes of rainbow hues that shift as you move the stone.
- Hardness: 5 to 6.5 on the Mohs scale, so softer than most gems.
- Anniversary: the gem for the 14th wedding anniversary.
October has two birthstones: GIA lists opal and tourmaline. This guide focuses on opal.
What causes opal's play-of-colour
Precious opal is made of sub-microscopic spheres of silica stacked in a grid-like pattern. As light passes between the spheres it diffracts, splitting into spectral colours. The size of the spheres decides which colours you see: according to GIA, spheres of about 0.1 micron produce violet, while spheres of about 0.2 microns produce red.
Where the name comes from
In Sanskrit, opal was called upala, a precious stone. In ancient Rome the name became opalus, which gives us the word we use today.
Types of opal
GIA divides opal into two broad classes: precious opal, which shows play-of-colour, and common opal, which does not. Within those, you will often see:
- White opal: play-of-colour on a light body; found in South Australia and New South Wales.
- Black opal: play-of-colour against a black or very dark body; Lightning Ridge in Australia is known for the world's finest.
- Boulder opal: fragments of the surrounding rock (matrix) become part of the finished gem; GIA notes it is mined only in Queensland, Australia.
- Fire opal: transparent to translucent with a yellow, orange or red body colour, and often no play-of-colour; also called Mexican opal, with Querétaro a known source.
- Ethiopian opal: from Welo in Ethiopia, a newer source known for vivid play-of-colour. Some Ethiopian opal is porous and can absorb water and chemicals, so it should be kept dry.
Australia is the world's most productive opal source, and opal is also found in Ethiopia, Mexico, Brazil and the United States, among other places.
Opal meaning and beliefs
Because it shows every colour, opal has long been regarded as one of the luckiest gems. Its folklore includes:
- The Romans saw opal as a symbol of love and hope.
- Bedouins believed opal held lightning.
- The ancient Greeks linked it with prophecy.
- In European tradition, opal stood for purity, hope and truth.
You may have heard that opal is unlucky. According to GIA, that idea comes from a 19th-century novel, not from ancient belief. Many people today wear opal as a symbol of hope and good luck.
These are traditional beliefs, not proven effects, and are no substitute for medical advice.
Opal treatments and doublets
Some opal in the market is impregnated with oil, wax or plastic, or given a sugar or smoke treatment to darken its body colour. Thin slices of opal are also glued to a backing to make doublets and triplets. Doublets and triplets can weaken if soaked for long periods, so it is good to know which you have.
Wearing and caring for opal
Opal is soft, with very poor to fair toughness, so it scratches easily. It is best in earrings and pendants, or in rings with a protective setting that you wear for occasions rather than every day.
- Warm, soapy water is the only safe way to clean opal.
- Never use ultrasonic or steam cleaners.
- Avoid high heat, sudden temperature changes and strong light.
- Store it apart from harder gems, which can scratch it.
Our jewellery care guide has more tips.
Shop the October birthstone
At Wanderlust Jewelry South Africa our founders hand-pick pieces from artisans in India, Thailand, Indonesia, Cambodia and Hong Kong, along with pieces made in South Africa. Because every opal is different, you are welcome to schedule a video call with one of our consultants to see the exact piece before you buy (WhatsApp 068 613 6350). Rings over R2,000 include a free first resize within 30 days (see our size guide).
Browse our opal jewellery or the full October birthstone collection.