Two common specimens these days are Rainbow Moonstone and Labradorite. Both of them have similar properties: internal flash, visible crystals, and the tendency to capture people’s eyes from across the room.
But how similar are they really? Is there overlap in their mineral families?
Read on, I’m going to help you mine to the root of the matter with a basic guide comparing rainbow moonstone versus labradorite.
What is Rainbow Moonstone?
Rainbow Moonstone is a milky-to-water clear form of feldspar with an internal low that ranges from blue to orange, with very rare specimens displaying some more unique colors.
The fire of Rainbow Moonstone is internal, showing up due to the way the crystals form and disperse light.
Rainbow Moonstone ranges from milky white to almost water clear, where only the small dividing sections between the crystals can be seen internally. Specimens with higher clarity and more fire demand higher prices.
Rainbow Moonstone is related to regular Moonstone, but it’s actually a slightly different species of mineral. Both are still feldspar, but they can be hard for the untrained eye to tell apart. The difference lies in the mineral’s components.
Rainbow Moonstone is a calcium-enriched plagioclase feldspar, while “normal” Moonstone is a combination of orthoclase and plagioclase which are a different sort of feldspar. It’s effect is caused by the inter-growth of crystals of those two materials.
Rainbow Moonstone, on the other hand, has an effect created by the slow growth of crystals occurring in different layers with the right amount of calcium. When the angles are right on the lamellar growth pattern you get the internal glow associated with the stone.
Rainbow Moonstone is a relatively new addition to the gem trade, but it’s rapidly become respected in its own right. It’s readily available, and often much cheaper than traditional moonstone for a stone of equivalent size.
What is Labradorite?
Labradorite is in the same species of mineral as Rainbow Moonstone. You’d do best to consider them like breeds of dog: while rather dissimilar in looks they’re still the same beast.
Labradorite is a triclinic feldspar mineral that has an iridescent schiller. Colors in labradorite range from yellow to blue in most cases, but orange and purple specimens are readily available as well. In some very rare cases, natural red is also found in labradorite.
Labradorite is usually a dull grey to black overall, with the optical effect providing all of the stone’s color when viewed. The “flash” is ideally cut to be front-facing, but sub-optimal cuts can lead to it only being viewed at an angle. Most Labradorite is at least superficially transparent, and the crystals are sometimes brownish or greenish-white instead of grey.
Labradorite is another common stone in modern use, particularly among amateur smiths and wire wrappers. The interesting visual effect is offset by the massive formations of the stone, so a good-sized cabochon of labradorite is often cheaper than any other “semi-precious” stone. It’s a good “bang for your buck” stone in jewelry or for mineral collections.
Like Rainbow Moonstone, Labradorite’s schiller comes from the intersection of different growth planes of crystals.
Extremely high-grade labradorite is often “flashy” from multiple angles, and when it’s combined with a solid background you’ll sometimes see it referred to as spectrolite. Spectrolite is an expensive stone, and often shows larger ranges of color than other specimens.
Other times, lower-grade samples are sold under the name to try and command a higher price.
But in the end, labradorite is simply a feldspar crystal with internal angles that create an awesome optical effect.
How Are They Similar?
Well… they’re pretty much the same thing just with slightly different formation.
For the most part, the dividing line between labradorite and rainbow moonstone is the colors of the background crystals. When transparent or milky with no hint of brown or green… well, that’s a Rainbow Moonstone. Black, grey, and brown backgrounds are usually simply called Labradorite.
The fact of the matter is that the stones are identical chemically, its only the later impurities that determine what it’s called.
Milky or transparent? Rainbow Moonstone.
Solid or off-white transparency? Labradorite.
The hardness, cleavage lines, and even the difficulty of working both are exactly the same. Your guess is about as good as anyone else’s in this arena since both only trade names of popular stones.
That said, I usually refer to opaque white-ish labradorite still as labradorite. It takes at least a few water-clear spots to upgrade the designation and any inclusions of brown or black take the stone out of the running as Rainbow Moonstone.
How Are They Different?
The differences are pretty superficial overall.
There is one big subjective effect that separates them: while the fire of both stones are due to internal formations, Rainbow Moonstone often appears to have the fire “floating” instead of sitting on the surface.
Likewise, Labradorite will often appear on the surface.
There are some stones in between. I’ve seen them sold under a number of different names, including “Frost Labradorite”, but the effect is… not great. These stones are often milky with dark spots and have little fire due to the lower clarity of the stone. The effect still seems to “appear” on the surface in these cases.
The truth is that there are only minor differences in how they look when you compare these stones. Other than that?
Rainbow Moonstone and Labradorite are the same stone, its just relatively minor cosmetic differences that set them appart.
How Do I Tell Rainbow Moonstone and Labradorite Apart?
Low-grade Rainbow Moonstone and low-grade Labradorite are very similar in appearance. The separating point between them is kind of nebulous and usually just depends on where the stone was mined.
In the picture above, you can see some of these in the center. Rainbow Moonstone very rarely has black specks inside of it but the majority is clear or a bit milky all the way through. Low-grade labradorite has a similar form but it’s much more opaque and has slightly different colors.
In higher grades, the differences are much more stark.
High-grade Rainbow Moonstone is water-clear with small internal portions where the crystal form can be seen. The schiller will seem to float in the center of the stone.
High-grade labradorite, on the other hand, will have an opaque background with a play of colors across the surface of the stone. Labradorite tends to have a wider range of colors, and in general a wider variance in what’s considered the same stone.
There’s no real push to sell Rainbow Moonstone as Labradorite, but on occasion, you’ll see low-end Labradorite for sale as Rainbow Moonstone. Most people are likely to just overlook this deception on basic principles. The Labradorite sold as Rainbow Moonstone is usually pretty terrible overall, mostly junky off-white cuts from better rough.
For the amateur… if it’s transparent then it’s Rainbow Moonstone but an opaque or translucent background is almost always Labradorite. But in the end, both of these stones are the same species!