Journal · In the hand
How to tell if moonstone is real
Tilt it. In a real moonstone the blue sheen travels across the dome as the angle changes. In glass it sits in one place and stays there. That single test settles most cases in about ten seconds, and everything below is how to do it properly and what else to look at.
The tilt test, step by step
This works because of where the light in a moonstone comes from. The stone is a feldspar with very thin alternating internal layers, and light entering the dome scatters between those layers before coming back out. The effect is called adularescence, and because it depends on the angle between the light, the stone and your eye, it cannot help but move when any of the three does.
Find one soft light. A window on an overcast day is ideal. One lamp in an otherwise dim room also works. What you want is a single source coming from one direction. Overhead office lighting is the worst case, because light arriving from everywhere at once gives the sheen nowhere to travel from.
Avoid direct sun. This is counterintuitive, and it is the mistake most people make. Bright sun floods the surface and overwhelms the sheen, and the stone reads as a plain pale pebble. If you have only sun available, step into shade first.
Rock it slowly. Hold the stone between finger and thumb and tip it through about ten or fifteen degrees, then back. Slowly, over two or three seconds each way. You are not looking for a flash. You are looking for the pale blue to cross the stone and settle at a different place than where it started.
Watch where the light sits, not how bright it is. Brightness varies with the stone and with the light. Position is what tells you. In a natural stone the sheen has a leading edge that moves, gets stronger at one angle, and thins out to nothing at another. In glass the glow is usually centered, evenly round, and it goes where the stone goes.
If you own a moonstone already, do this now with it before you need to judge an unfamiliar one. Five seconds with a stone you trust teaches you more than any description, including this one.
What opalite actually is
Opalite is glass. That is the whole answer, and it is worth saying plainly because the name suggests a mineral and there is no mineral by that name. It is manufactured, usually milky white with a faint blue cast, and it is often quite pretty. What it is not is a stone: it has no crystal structure, no internal layering, and no adularescence.
The word turns up in a few forms, and none of them are official mineral names: opalite, sea opal, opal moonstone, and occasionally just moon glass. Where the label uses a compound name like that, it is worth asking what the material is. And where a label says nothing at all, the absence of the word glass is not evidence of anything.
Side by side, the two are easy to separate once you know what to compare.
| Moonstone | Opalite (glass) | |
|---|---|---|
| What it is | Natural feldspar | Manufactured glass |
| Where the light comes from | Scattering between internal layers | Surface and body of the glass |
| Does the glow move? | Yes, it travels as you tilt | Usually no, it stays put |
| Inside the stone | Some texture almost always | Clean, often with small round bubbles |
| Hardness (Mohs) reference only, not a test |
6 to 6.5 | About 5.5 |
One caution about that last row. The hardness figures are there for context, not as something to act on. A difference of half a point to a point is not something a fingernail or a steel point can find, and any scratch test means damaging the stone to learn about it. The three things worth actually doing are all non-destructive: watch whether the sheen moves, look for internal texture, look for bubbles.
Three more things to look at
Look for texture, not against it. Natural moonstone usually has something inside it: faint feathery lines, small inclusions that look a little like centipedes under magnification, a cloudiness through part of the dome. This is the opposite of a flaw. A stone with a little internal life is more likely to be a stone. Perfectly clear all the way through, with an even glow parked in the middle, is what manufactured material looks like.
Use a flashlight for the inside, not the sheen. Held beside or behind the stone, a small torch lights up internal texture and tells you whether there is any. Pointed straight at the face it washes the adularescence out completely, for the same reason sunlight does. Two different jobs, two different positions.
Bubbles are decisive. If you can see small perfectly round bubbles inside, that is glass. Gas bubbles form in a melt. They do not form in a feldspar crystal. You may need a loupe, and you may find nothing, but if you do find them the question is answered.
What this page is not doing
Three things, deliberately.
It is not suggesting that the trade is full of fakes. Most sellers describe their material accurately, glass beads have their own honest place in jewelry, and someone selling opalite as opalite is selling something real. The reason to know the difference is so you know what you have, not so you can assume the worst of anybody.
It is not settling the naming questions. There are several trade names in circulation for stones with a similar sheen, and whether two of them are the same species is a question for laboratory testing rather than for a page like this one. I am not going to make a determination I cannot back with a report.
And it is not asking you to take my word for my own stones. Every moonstone I set is natural, but a promise from a seller is the weakest kind of evidence there is, which is why this page teaches the test instead. Do it to the stone I send you. That is a better arrangement than trust.
If you want the wider context: moonstone is one of June's three birthstones, the case for each sign is set out here, and Cancer is where the stone started.