Is your moonstone real?

The glow should move, not sparkle

Real moonstone does one thing, and it does it the same way every time. Tilt it slowly under a light. A soft blue-white glow sweeps across the stone like a torch beam, and it looks like it is floating just under the surface. Turn it past that angle and the glow goes out.

That glow comes from paper-thin layers inside the stone bouncing light back at you. It is soft and cloudy, white to pale blue, or warm peach in peach stones. If you see a rainbow of separate colours, or glitter sitting on top that does not move when you tilt it, that is not moonstone.

Opalite is glass. A phone torch catches it

The usual stand-in is opalite, a milky man-made glass sold as sea opal or opalite moonstone. Hold your phone torch behind it. Opalite lights up warm orange. Now look at it against something dark with the light in front. It turns cold blue. Real moonstone stays white-blue both ways. That orange to blue flip is the giveaway.

Then look close, with a loupe if you have one. Glass holds tiny round bubbles, swirl lines and a seam near the drill hole. Moonstone holds none of that. What it does have is short straight cracks stacked in a row, like insect legs running through the stone. Collectors call them centipedes. Find those and you are almost certainly holding the real thing.

Two tests you can do at the kitchen table

Moonstone is a feldspar, and it sits at 6 to 6.5 for hardness. That is a useful spot. A steel knife or nail is about 5.5, so it will not scratch real moonstone. Glass is about 5.5 too. So if a steel blade marks your stone, it is not moonstone. Test on the back or a hidden spot, never on the face you look at.

Feldspar also splits along flat planes that meet at about a right angle. Look at any chipped edge. You may see flat little steps that all catch the light at once as you turn it. Glass never does that. Glass breaks in smooth curved shells with sharp lips.

Rainbow moonstone is a different mineral, and that matters

Most of what is sold as rainbow moonstone is white labradorite, a plagioclase feldspar, not the orthoclase that adularia moonstone comes from. It is a real stone honestly worth buying, and the flash is genuine, but it is a spectral flash of blue, gold and green, labradorescence, rather than the soft single-toned float of true moonstone. If you were charged a premium for classic Sri Lankan blue-sheen moonstone and received a rainbow flash, you were sold something else.

The other honest lookalikes are milky quartz, which is uniformly cloudy and has no moving glow, chalcedony, which is waxy and inert, and selenite, which is so soft your fingernail marks it. Selenite at hardness 2 is the fastest of all to rule out.

Sources, price and what an obvious bargain means

Good material comes from Sri Lanka, India, Madagascar, Myanmar, Tanzania and Virginia in the United States. Sri Lankan blue-sheen stones with a clear body and a strong beam are the expensive end. Indian material is more plentiful and more included, which is why it is cheap and why it is also where most honest tumbles come from. A large, perfectly clean, strongly glowing bead strand priced at a few pounds is glass, because the rough for that stone would cost more than the strand.

Care, once you know it is real

Those same two cleavage planes make moonstone brittle. It chips on impact and cracks with sudden temperature change, so keep it out of an ultrasonic cleaner and out of boiling water. Warm water, mild soap, a soft cloth. Store it away from quartz and topaz in a jewellery box, because anything harder than 6.5 will scratch it in a drawer.