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If you’ve ever wondered how a moonstone seems to glow, whether or not it’s even natural, or what else is interesting about it, chances are the answer to all your questions lies in the profound process in which it forms.
Many wild stories have been told about this stone which is actually made of some of the most common mineral ingredients on earth. Its popularity and beauty have caused several copy-cat minerals to come to light, some natural and some manmade, which make it tough to identify a moonstone when you see it.
However, its geological properties set it apart from these stones and one needs only to perform some simple tests to tell for sure.
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What is Moonstone?
The beauty of moonstones has been adored in ancient Hindu mythology, through Greek and Roman culture, to the Art Nouveau period of modern history.
Modern geological science has uncovered the mysteries behind its appearance which stumped so many cultures before – boiling it down to a complex formation process undergone by common minerals.
Moonstone is a variety of feldspar, itself a mixture of silica and aluminum. Some of its properties, such as the colorful glow which characterizes it, called adularescence, come from the process by which it forms. With other important properties such as its perfect cleavage, color, and refractive index, its adularescence makes this coveted gemstone unique.
Not having the scientific resources and methods which exist today, all major mythologies in which it makes an appearance associated moonstone with lunar powers because of its typical light feminine colors and soft glow.
The Romans thought that it was made of frozen moonlight. The stone was used in connection with the deity Luna and could be found at many of her places of worship.
Moonstone’s Hindu lore speaks of the stone being embedded in the forehead of the Hindu moon-god Ganesh.
During the Art Nouveau period, moonstone was used in intricate jewelry which sported curves and flamboyance typical of the time. The stone itself was cut in smooth curves.
Moonstone is a type of feldspar, which as a whole, accounts for 60% of the minerals on the crust of the earth. Its chemical formula is KAlSi3O8.
It has the possibility of displaying several different colors: typical varieties are colorless, white, beige, or silvery blue, but it has been known to commonly show up in green, darker brown, or reddish-brown as well.
It displays perfect cleavage, which can cause it to be very fragile even with a Mohs hardness of 6-6.5. Perfect cleavage means that the stone breaks along flat planes which can reflect the light easily because of an absence of imperfections.
The key attribute of moonstone is its adularescence. In finer specimens of moonstone, the mineral’s adularescence takes the form of a distinct gleam coming from the center of the piece.
This gleam can sometimes expose the internal structure of the stone, which consists of a multitude of minuscule layers, which if well defined will take the form of a square lattice inside the piece. Lower quality moonstones exhibit a shimmer or very little adularescence at all, especially if unpolished.
How is a Moonstone Formed?
The internal structure of moonstone, which is responsible for many of its unique properties, comes directly from the amazing process which forms it.
Such a unique process is the result of the slightly different chemical properties of the specific feldspar varieties which form it.
Two types of feldspar is characteristically cool at slightly different temperatures. When found together in magma cooling at a specific slow rate, this difference causes them to separate into microscopic layers as they harden. The layers refract and trap light differently once solid, and this causes the characteristic ivory to shine.
The two varieties of feldspar which make up moonstone are orthoclase and albite. The slow rate of their cooling allows the first constituent to harden well before the second.
As it hardens, the material which is still liquid has a tendency to stick together, but while the two feldspar types have such similar densities, the liquid cannot travel very far.
The microscopic layers form as a result of the first ingredient solidifying into a lattice while fighting for space with the liquid ingredient.
The liquid layers then start to solidify. In the absence of any foreign disturbance, the gemstone structure is determined at this point and needs only to harden before it becomes a gemstone.
If other minerals are present during this process, it is easy to see how the fragile system could be disrupted, either by a liquid persisting after everything else solidifies or a solid forming too early, breaking the lattice, and a lesser quality stone produced as a result.
Similarly, with too quick of a cooling process, both ingredients solidify at similar times and don’t have time to form the exact crystal structure.
BTW: Do you want to know more about rocks and minerals identification? The books listed below are the best ones you can find on the internet (Amazon links):
- Smithsonian Handbooks: Rocks & Minerals
- Gemstone & Crystal Properties (Quick Study Home)
- Ultimate Explorer Field Guide: Rocks and Minerals (National Geographic Kids)
How to tell if Moonstone is real?
It is true that the moonstone has been revered throughout human history, but it’s also valuable today as a gemstone. Like anything valuable, people have found a way to reproduce it with disturbing accuracy.
If you’ve found a gemstone in a rock or jewelry shop and you are wondering if it is real, this section can help you. If you’ve found a stone in the natural world and you think it might be a moonstone, the section detailing the identifying process is for you.
Opalite, labradorite calcedony, and many cloudy/milky colored stones, especially if they are of higher quality, are sometimes able to mimic some properties of moonstone, even though they have a chemical composition far from it. Adularescence is a good giveaway that you’re looking at a moonstone, but if it looks too shiny to be true, it may be labradorite, aka rainbow moonstone.
If the gleam is showing bright colors but seems to be coming from the surface of the stone, it may be an opal. If it seems duller or less refractive than many pictures you’ve seen of moonstone, it may be calcedony.
Opalite is also often confused with moonstone because it displays a shimmer that can be typical of adularescence. However, this is a glass that is man-made to mimic the qualities of moonstone. If you’re in a store, this could also be sold as opalite moonstone, opalite quartz, or sea quartz.
Labradorite is also sometimes confused with moonstone because of its color. In fact, a variety of labradorite is called rainbow moonstone.
The difference between this stone and real moonstones is that this stone is nearly perfectly clear, while even the clearest moonstones will have a more cloudy color.
TIP: The problem with fake rocks has been quite common in the last few years. And one of the most frequently faked rocks are geodes which are really popular gemstones. Learn how to know the difference between real and fake geodes:
How to Identify Moonstone?
Geologists typically field-verify the identity of a stone by leveraging its known properties, such as hardness and cleavage, and performing tests to match the performance of the sample to how they know a sample of a certain mineral would act.
The best way to immediately recognize a moonstone is from its adularescence. It can look different depending on the sample. Hold the stone in light and examine it for translucent or semi-transparent areas and try to deduce whether or not it reflects or emits light differently than you’d expect.
If you have a raw sample, it should still show smalls signs of this property, but washing the stone is a good place to start.
If you are still not sure, chisel off a small impurity in the sample or just simply chip off a small piece and see if the exposed area displays these symptoms. If you cannot identify adularescence in your prospective moonstone, you’ll have to resort to more complicated tests.
Before you get out your hardness testing kit, let’s sit back a second and examine that glint you’re catching but don’t want to jump right in and characterize it as adularescence.
One way that it can appear is so distinguishing that the effect has been given a name: “cat’s eye.” Many stones reflect light well, but the structure of moonstone causes the light to not only reflect directly but also permeate deeper inside the stone, being visible sometimes as faint lines crossing in a geometric “X” behind the main reflection.
Another way that adularescence can present itself in moonstone is under the surface. The scattering of light through the stone will sometimes cause different colors to appear outside of the reflection area.
Hold your stone in the light and turn it around slowly, looking for light or colors which don’t follow the same path as the reflection.
If you don’t see any of these telltale signs, it is possible that your moonstone is too dirty or just shaped in such a way as to inhibit this glowing property. If so, test it for hardness.
Typically, stones that show similar properties to moonstones, such as opal, chalcedony, or labradorite are much harder or softer than moonstone’s 6-6.5 rating.
Does Moonstone Come from the Moon?
All the remembered theories for moonstone’s unequaled qualities which were developed before modern science have something to do with the moon.
While we now know that moonstone is formed from feldspar, one of the most abundant substances on earth, it does not come from the moon. Feldspar is also found abundantly on the moon’s crust, but potassium feldspar is very rare and therefore it is quite improbable that any moonstones exist on the moon.
To crush the myths and lore created by all these fabled civilizations about moonstone with what seems like basic science seems a bit of a shame. However, I see it as a testament to the geological wonders that this world can actually create.
Something with the beauty that demanded an ethereal explanation from some of the most pioneering civilizations happens quite naturally through physical processes right here on earth. Oh, the wonders of gemstones!
TIP: So the moonstone does not come from the moon, unfortunately. But don’t be sad, some rocks really come from the moon. The real Moon rocks. Read more about them here:
Do Moonstones Glow in the Dark?
Moonstone sometimes displays the type of light neon green, blue, and pink hues which characterize phosphorescent materials.
They also emit light from positions that seem unnatural, sometimes far away from the point of reflection. This could make some believe that moonstones are phosphorescent.
However, moonstones are not phosphorescent materials, and therefore do not glow in the dark. Such materials are unique in the fact that they emit stored energy in the form of light. While moonstones store energy just like all materials, this energy is given off, as is typical, in the form of heat.
All myths that moonstones glow in the dark come from the astonishing property of adularescence making complex reflection patterns seem like emitted light.
If there is not light currently shining on a moonstone, it will not display its adularescence. However, just because they don’t “glow” in the dark, doesn’t mean they cannot produce some pretty interesting effects when combined with the right light/dark placement.
If you’re looking for a glow-in-the-dark effect, direct a small amount of light at a moonstone with a dark background, and if it is positioned correctly, its adularescence may seem to glow in the dark.
Is Moonstone a Natural Stone?
We’ve already learned some other natural and manmade stones that approximate moonstone and some ways to make sure the specimen you are looking at is actually moonstone.
Real moonstones are completely natural stones that form when two specific feldspar minerals solidify slowly from magma into stone, giving them time to separate because of different melting temperatures and form minuscule layers, which reflect light between them in a complicated way to form the phenomenal sheen that is exhibited by moonstones.
Opalite is an unnatural stone that is made to look like moonstone. Opalite is glass that is made from small spheres of SiO2 (silicon dioxide) which are stacked in a geometric pattern.
High temperatures melt the mixture into the glass. It sometimes contains air bubbles which are a result of impurities in this process. It can look blue or milky white depending on the background. However, it is completely separate from the moonstone.
Is Moonstone a Precious Stone?
There are many different ways moonstone can present itself, and while all of them are moonstone, some are considered different quality than others.
The value of moonstone and its label of precious vary from specimen to specimen. Clear-blue moonstone is rare, especially in large sizes, and is, therefore, a precious gem. Other kinds of moonstone, especially those which do not exhibit as strong of an adularescent behavior, are not considered precious because they are widely available to buy and easy to find in the right place.
If you want to find a moonstone, and trust me there is nothing more exhilarating than finding a gemstone in its natural form, you’re in luck because they are found all over the world.
The next article in this series will tell you where to look. If you want to know the value of moonstone or how to find out the value of a specific moonstone specimen, the last article in this series will tell you all you need to know.
TIP: Do you want to know how and where to find moonstones in the world and in the USA? Or know how valuable moonstones can be? If so, check out these ultimate guides below: