Sold loose and unset, this is a 17.4 carat Ceylon moonstone — 19.12 ratti — at Rs. 11,630, which is about Rs. 668 per carat.

Buying a loose stone

Buying the stone first and commissioning the setting afterwards is the older way of doing things, and for a piece this size it is usually the better one. Your jeweller can build the mount to the stone's actual dome and girdle rather than forcing a large cabochon into a ready-made head, and you keep control of the metal, the shank width and whether the stone is bezelled or clawed. For moonstone, which is 6 to 6.5 on the Mohs scale and splits more readily than it chips, a bezel made to measure is genuinely worth the extra work.

The blue

The soft blue in this stone is adularescence: light scattering off layers inside the feldspar that are thinner than a wavelength of light. It is not pigment, which is why it moves when the stone moves and disappears if you hold it flat to a dull light. Judge any moonstone by rocking it slowly under a single light source rather than in flat daylight — that is the only way to see what the sheen really does.

What the rate tells you

At Rs. 668 per carat this stone sits just below the middle of our collection, where rates run from roughly Rs. 481 to Rs. 776 per carat. Three of the large Ceylon stones here are priced within forty rupees a carat of each other, so at this size the choice between them comes down to the stone in front of you rather than the arithmetic.

Care

Warm water, a little plain soap, a soft cloth. Never an ultrasonic cleaner, never steam, never bleach or ammonia. Store it separately so harder stones cannot scratch the polish, and take the ring off before anything involving a hammer, a gym or a kitchen sink.

Recorded as a Ceylon stone. Treatment has not been tested, and we record that rather than calling it untreated. Dimensions and clarity are not recorded yet — ask us and we will measure it.

This particular stone

This listing is one natural moonstone with a weight of 17.4 Carat. Its price is Rs. 11,630 — roughly Rs. 668 for each carat. Origin: Ceylon (Sri Lanka). Treatment: treatment not tested. Quote reference GS-000415 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.

Above twelve carats you are into collector territory. Pieces this heavy are usually set as pendants or kept loose, and they are prized for the size of rough they came from. If you do set it, choose a bezel or a heavy claw to protect the edges.

On the Mohs scale moonstone rates 6 to 6.5. That is middle-of-the-road hardness: comfortable in pendants and earrings, and in rings worn with some care. Store it apart from harder stones so it does not pick up scratches, and wipe it with a damp cloth rather than scrubbing.

Whoever you buy moonstone 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 moonstone 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): Moonstone is usually untreated. 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.