A 2.10 carat Australian opal is an easy stone to like. Here is what to check so that liking it turns into being sure of it.

• Quote reference AG-000569 when you message us on WhatsApp.
• It is solid opal; we do not sell doublets or triplets.
• At 5.5 to 6.5 on the Mohs scale it scratches more easily than ruby.
• Look at the colour in daylight first, then under a room lamp, turning it slowly.
• Check for fine cracks running through the body and tell us straight away if you see one.
• Smoking and sugar-staining exist in the opal trade, so ask what is known about this piece.

Heat is opal's enemy. A sunny windowsill or a car parked in a Karachi afternoon can dry it out and start a crack. Keep it in a pouch in a cool drawer. There are more pieces to compare in the opal range, and the basics are in our gemstone buying guide.

With Cash on Delivery you can work through that whole list with the rider at the door before you pay, and you still have 7 days to return it.

This particular stone

This listing is one natural australian opal with a weight of 2.1 Carat. Its price is Rs. 10,500 — roughly Rs. 5,000 for each carat. Origin: Australia. Treatment: treatment not tested. Quote reference AG-000569 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, 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. No lab report yet; independent testing welcome. 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.