Moonstone has been a popular gemstone from antiquity. The Romans frequently used the gem in their jewelry, and it continued to be valued through the medieval period in Europe. The stone is also seen in classic jewels from India and the Middle East. A revival occurred in the Victorian period, and it is often seen in Art Nouveau and Edwardian jewelry (1880's - 1910's).
Moonstone, along with Pearl, is the birthstone for the month of June.
Burmese Blue-Glow Moonstone with Bamboo-shape Inclusions (this phenomenon can also occur in Sri Lankan material)
What a Moonstone is...
There are several varieties of feldspar minerals which are sold under the name "Moonstone." Traditionally, Moonstones are white, translucent to opaque stones which display a wispy sheen when light moves across the surface. This effect is called adularescence.
Moonstone properly is a combination of feldspar minerals, composed of plate-like layers (lamellae) of albite feldspar along with layers of either orthoclase or sanidine feldspar.
The adularescent sheen or glow can range from a lighter shade of the base color, to silvery, to light blue. This luster is caused by alternating layers of different feldspar minerals interfering with the light hitting them and reflecting only certain wavelengths back to the viewer. The thinner these layers, the more the sheen tends towards blue.
The major source for true Moonstone is Sri Lanka. Other important deposits are found in India, Myanmar, Brazil and the U.S. (Virginia, New Mexico).
Moonstones have a Mohs hardness of 6 to 6.5. Stones can be fragile, and can crack along the lamination layers, and so are best not used in jewelry which is subjected to hard knocks.
Cuts commonly encountered...
Moonstones are usually cut as cabochons, which displays the luster to advantage and also makes for a stone less likely to chip.
Moonstone rounds which are drilled for use as beads are another popular use of the stone. A simple necklace made of graduated, fine moonstone beads can be spectacular alternative to Pearls.
Occasionally, one sees stones that have been carved for focal beads, pendants or ring stones. Gems which have been faceted are also sometimes seen.
Types usually seen...
Classic White Moonstone
- Adularia - the classic "Moonstone" is mainly composed of alternating layers of orthoclase and albite Feldspars. It was named after a mountain in Switzerland where there was an early mining site.
- Burmese Blue or "Blue Glow" - a highly desirable transparent variety from Myanmar which displays a floating blue adularescence. These have become rare in recent years. A Burmese stone with golden rutiles is pictured at the top of this article. An orthoclase variety known as peristerite has much the same appearance, and is often sold as "Blue Moonstone" and sometimes "Rainbow Moonstone," though it is differs slightly in composition from the traditional moonstone varieties.
- Rainbow Moonstone - This gemstone, which came on the market during the 1960's, is a different material than the traditional moonstone. It is actually a variety of labradorite (found in India, Sri Lanka and elsewhere) being marketed under the names "Rainbow Moonstone" and "Blue Rainbow Moonstone." Gems of this stone can range from a milky white to transparent, and some of the lower grade stones display a platey structure which looks more like a white version of common labradorite, than it does any true Moonstone. The "rainbow" labradorite gems exhibit some combination of blue, green, lavender and/or orange glow which is produced by the same Labradorescence phenomenon found in labradorite/spectrolite. Instead of light bouncing between layers of orthoclase/sanidine and albite, the Rainbow Moonstones get their iridescent sheen from light being reflected from twinning planes within the stone. While this variety of labradorite is certainly attractive, it is not properly a Moonstone, does not have the rarity or appearance of, and should not be confused with, true Moonstone. It would be better to eliminate the confusion by calling it something else, so that it could stand on its own merits.
- Black Moonstone or Blue Norwegian Moonstone - This is actually a stone which is called larvikite, a mixture of plagioclase and alkali feldspars. Having a dark, grainy background, larvikite gives off a bluish shimmer which recalls some forms of labradorite/spectrolite (though larvikite does not show broad areas of flash, as do the latter). Again, this stone is not a true Moonstone.
- Cat's Eye - These display an adularescent stripe which rolls across the stone's face as light moves around the stone.
Black, Green and Silver/Brown (India)
- Colored Moonstones - While white is the architypical color for Moonstone, there are also pinks, blues, greens, grays, oranges, and tan/brown varieties. Any color is due primarily to traces of iron.
- Star Moonstone - Usually opaque, this type shows an adularescent 4-armed star on the stone's top when lighted from certain angles.
What to look for...
- When comparing stones, the more translucent stones are more valued than those which are opaque. Transparent stones which are free of visible inclusions are desirable.
- The adularescence should be easily seen.
- Gems having a fine blue glow are usually more expensive than stones showing silver or other shades.
- Stones which display a cat's-eye or star are rarer, and priced accordingly. When looking at these types of gems, you want the visual effect to be well-defined.
- Although you may personally prefer another type of Moonstone, the most valuable varieties of Moonstone are the nearly transparent true Blue Sheen or Blue Glow Moonstones from Myanmar (Burma).
After noting the above, I should mention that you can find special Moonstone gems which are very attractive and desirable, yet do not fall into line with the general guidelines above. Like other members of the feldspar family of gemstones, individual Moonstones can possess one-of-a-kind characteristics which supercede the normal rules of thumb. Uniqueness is part of the charm of many gems types found in the feldspar group - unlike other precious stones where uniformity is prized.
The first thing to look for when identifying Moonstone is whether it has a single-color glow inside stone (not on the surface) that shifts with the light.
"Jelly" (or "Crystal") opal is sometimes mistaken for Moonstone. However, its glow is often multicolored, and isolated to specific areas inside the stone.
The spectrolite form of labradorite is a related gem that is sometimes mislabeled. However, this has multiple colors which pop into view as the light travels over the stone. Spectrolite's colors seem to lie closer to the surface, and not be deep inside the stone (as in Moonstone).
There are also "Rainbow Obsidian" and "Velvet Obsidian" ("Sheen" obsidians) that also have more than one color. The multi-color display is somewhat similar to spectrolite, but the pattern is more diffuse, and the colors are arranged in layers.
Then there are Schiller, Star and Cat's Eye effects, that are exhibited by various stones. But these effects are sharper, and not really a glow.
Finally, there are also a very few other stones which can dispaly effects similar to Moonstone, such as valentianite. But these are uncommon enough that they almost never make it into manufactured jewelry (though collector gemstones such as this are occasionally mounted in one-off artisan pieces).
Imitation Moonstone "gems" are common in costume jewelry. The imitations which come closest to the real thing are made of glass. Plastic is also sometimes substituted. Both are softer than real stones, and easily detected.
Laboratory-synthesized Moonstones have been produced, but thus far the cost has been too high to compete with the real thing. Other varieties of milky-white stone have been labeled as or substitued for Moonstone - though these bear only slight resemblance to the true gemstone.
Things to be aware of...
Moonstone should not be placed worn jewelry that will be regularly exposed to hard knocks or abrasion. When storing, protect it from coming into contact with (and being scratched by) harder stones such as diamond, topaz, beryl, rubies, tourmaline and sapphires.
Although used by some, it is probably best to avoid cleaning Moonstone in an ultrasonic cleaner (especially the "Rainbow" types). Avoid cleaning with steam or exposing to heat, as well as contact with chemicals. Use warm, soapy water to clean and promptly rinse in cool water.
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