"Precious opal" is one of the few opal terms with a real gemmological meaning, and it is worth knowing because it separates the gem from the gravel. Precious opal is opal that shows play-of-colour. Opal that does not is called common opal, or potch, and it is worth almost nothing — the same mineral, without the ordered internal structure that makes colour happen.

The stone

1.75 carats, which is 1.92 ratti. Shape: oval cabochon. Origin: Australia. Rs. 8,750, about Rs. 5,000 per carat, reference GS-000605.

Note the rate. At over Rs. 8,500 per carat this is one of the highest in our collection, on one of the smallest stones — which tells you everything about how opal is priced. Weight is almost irrelevant; fire is almost everything.

Precious, common and the difference

• Precious opal has silica spheres stacked in an orderly grid, which diffracts light into colour. This stone is precious opal.
• Common opal (potch) has the same chemistry but disordered spheres, so no colour. It is often milky, grey or black, and it is what the dark backing of a doublet is usually made from.
• The two occur together. A thin seam of precious opal running through potch is the normal way it is found, which is why so much opal is cut thin and why doublets exist at all.

Judging quality within precious opal

Once a stone is precious opal, the grading that matters is brightness and body tone, both measured on recognised scales, plus which colours appear and how much of the face they cover. Red and orange fire is scarcer and dearer than green and blue. Broad, defined flashes are worth more than fine scattered pinfire. A stone that keeps firing through a wide range of angles beats one that flashes once and goes quiet. Our Australian opal buying guide works through the scales properly.

Why a small stone can cost this much

Because precious opal of real brightness is scarce, and because thin seams mean large bright stones are rarer still. A 1.75 carat cabochon with strong fire is a more notable piece of material than a five carat one with quiet colour — and our listings reflect that, with the larger stone costing a fifth as much per carat.

Solid opal

We sell solid natural opal, not doublets or triplets. Check any opal edge-on for the straight glue line where layers are joined — with a thin precious seam the temptation to back it is exactly why doublets are common. See our real versus fake opal guide.

Treatment and care

Solid opal is usually untreated, though some is smoke- or sugar-treated to darken the background; this stone has not been tested and the specification says so. Opal is 5.5 to 6.5 on the Mohs scale and holds water: soft damp cloth only, never ultrasonic or steam, and keep it out of prolonged sun and dry heat.

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 — WhatsApp +92 308 887 3888.

This particular stone

This listing is one natural australian opal with a weight of 1.75 Carat. Its price is Rs. 8,750 — roughly Rs. 5,000 for each carat. Origin: Australia. Treatment: treatment not tested. Quote reference GS-000605 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.

Under two carats, a stone like this sits neatly in a slim ring, a stud or a delicate pendant and does not snag on sleeves. It is also where many first-time buyers begin when a stone is recommended for astrological reasons, because the total cost stays modest.

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.