Moonstone
Moonstone doesn't sparkle. It glows — a soft blue-white light that seems to sit under the surface and move as you turn the stone. That effect has a name, a cause, and a set of consequences for how it should be cut and set.
What causes moonstone's glow?
Moonstone is a feldspar that formed as two minerals intergrown in alternating microscopic layers. As light enters, it scatters off those layers and comes back out diffused, so the glow appears to float somewhere below the surface rather than reflect off it. The effect is called adularescence.
Because it depends on the internal layering, the cutter has almost no freedom: the dome must be oriented so the layers sit parallel to the surface. Get it wrong and the stone is simply cloudy. This is why moonstone is nearly always cut as a cabochon and almost never faceted.
Is rainbow moonstone real moonstone?
The stone sold as rainbow moonstone is, mineralogically, a white labradorite rather than true adularia moonstone. The trade name has been in use so long it is effectively standard, and the material is genuine and lovely — the flashes run blue through gold and violet against a translucent white body rather than the single blue sheen of classic moonstone. Worth knowing what you own.
What should you look for in moonstone?
Body as colourless and transparent as possible, with the blue sheen strong and covering the whole dome rather than a stripe across the middle. Hold it at arm's length and tilt: the glow should roll across the stone evenly. Cheap material shows the sheen only at one angle, then dies.
Is moonstone durable enough for daily wear?
Mohs 6 to 6.5 — but hardness is not the issue. Feldspar has pronounced cleavage, meaning it can split along internal planes if struck. A sharp knock on a hard edge does more damage to moonstone than years of ordinary wear. Set it protected, and take a moonstone ring off before anything involving your hands and heavy objects.
How do you care for moonstone?
Warm water, mild soap, soft cloth, dry thoroughly. Never ultrasonic — vibration and cleavage are a bad combination. Avoid sudden temperature changes, and store it away from harder stones.
Why is moonstone a June birthstone?
One of June's birthstones, and the one with the longest association with cycles, tides and intuition — a reputation earned honestly by a stone that appears to hold light the way water does.