A multicolour opal is one where more than one colour fires from the same stone, and it is worth more than a single-colour stone of the same size for a reason that comes down to geology rather than taste.

The stone

2.55 carats, which is 2.80 ratti. Shape: oval cabochon. Origin: Australia. Rs. 12,750, about Rs. 5,000 per carat, reference GS-000608.

Why several colours is rarer than one

Opal's colour comes from microscopic silica spheres stacked in a regular grid, diffracting light the way a soap film does. Sphere size decides the colour: small spheres give blue and violet, larger ones give orange and red. For a single stone to fire several colours, the sphere size has to vary across the piece while staying ordered enough in each zone to diffract at all. That is a harder trick for nature than producing one uniform colour, which is why multicolour material costs more.

It also explains the colour ladder. Larger spheres are scarcer than small ones, so red and orange fire is rarer and dearer than blue and green. A stone that produces warm colours alongside cool ones is doing two scarce things at once.

How to judge one

• Count the colours, then weigh them. Two bright colours beat five faint ones. Faint extra colours are not a feature.
• Check from several directions. Some opal fires only from one angle. A ring is seen from everywhere, so a stone that works through a wide arc is more wearable.
• Look for dead ground. Patches with no colour at all pull the value down sharply, even if the rest is brilliant.
• Watch it move. With opal a video tells you far more than a photograph. Ask us on WhatsApp at +92 308 887 3888 and we will send one under moving light before you order.

Is there a formal grade for this?

Not for "multicolour" as such. What is formally graded is body tone — the background the colour sits against — and brightness, both on recognised scales. The colours a stone happens to produce are described rather than graded. Be slightly wary of any seller who quotes a "rainbow grade" as though it were an official thing. Our Australian opal buying guide sets out the real scales.

Solid, not a doublet

We sell solid natural opal. A doublet is a thin slice glued to a dark backing and a triplet adds a clear cap; both can look spectacular face-up and are worth a fraction of a solid stone. Look at any opal edge-on for the straight glue line. See our real versus fake opal guide.

Treatment

Solid opal is usually untreated, though some is smoke- or sugar-treated to darken the background and make colour look stronger. We have not tested this stone, so the specification says so rather than claiming it is untreated. Independent testing can be arranged.

Care

Opal is 5.5 to 6.5 on the Mohs scale and holds water in its structure. Soft damp cloth only — never ultrasonic or steam. Keep it out of prolonged direct sun and dry heat, which can craze the surface. Ask for a bezel setting rather than claws.

Ordering

One piece only. Flat Rs. 500 delivery anywhere in Pakistan, insured and tracked, dispatched in one to two working days. Cash on Delivery, seven days to return it unused. Measurements on request. More in the Australian opal collection.

This particular stone

This listing is one natural australian opal with a weight of 2.55 Carat. Its price is Rs. 12,750 — roughly Rs. 5,000 for each carat. Origin: Australia. Treatment: treatment not tested. Quote reference GS-000608 when you message us about it. The photographs show this exact stone, so what arrives at your door is the piece you chose on screen.

Between two and six carats is the range most people choose for a gents' ring or a noticeable pendant. Here colour drives the price more than size does, which is why two stones of near-identical weight can be priced very differently.

Whoever you buy australian opal from, make sure of three things: the stone is natural rather than lab-grown, glass or glass-filled; any treatment is stated in writing; and the weight quoted is the weight of the finished stone. We check every australian opal for those three points before it is listed, a certificate is available on request, and because you pay on delivery you can look at the stone — or have it tested — before any money changes hands.

We sell natural stones only and inspect each one before it is listed. Treatment for this stone: Treatment not tested. Certificate available on request. As general background (not a statement about this stone): Solid opal is usually untreated; some opal is smoke- or sugar-treated, and doublets/triplets exist — we sell solid natural opal. Ask us on WhatsApp and we will tell you what we know about this exact stone; independent lab testing is available on request.

A certificate of authenticity is available on request for this stone, and independent laboratory testing can be arranged. Because you pay on delivery, you can also take the stone to a lab of your choice within the 7-day return window. Read more on our authenticity page.