Moonstones have been popular 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 Rutile

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 sheen when light moves across the surface. This effect is called adularescence.

Moonstone properly is a combination of Feldspar minerals, composed of layers of Albite Feldspar alternating with layers which usually are 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. 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.

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 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.

True Rainbow Moonstone

• Rainbow Moonstone - true Rainbow Moonstone exhibits a multicolored adularescence composed of some combination of blue, green and orange.
• Rainbow "Moonstone" - It is increasingly common to find a translucent, white variety of irridescent Labradorite from India and Madagascar being sold under this name. This unfortunate mis-naming is deceptive, and this type is a much less valuable stone than true Rainbow Moonstone. These gems exhibit a blue flash which more strongly resembles the Labradorescence found in Labradorite/Spectrolite, than the softer, ghostly glow displayed by true Moonstone. While this type of Labradorite is certainly attractive, it is not a Moonstone, does not have the rarity or appearance of true Rainbow Moonstone, and should not be confused with 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

• 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 true Rainbow Moonstone (not to be confused with Labradorite stones sold under the same name), and nearly transparent true Blue Sheen 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.

Similar Stones...

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 float across 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 rare enough that they almost never make it into jewelry.

Valentianite

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.

Like many types of gems, Moonstone should not be cleaned in an ultrasonic cleaner (which can crack stones). 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.

If interested, I have submitted other Guides:
Gems related to Moonstone
Other Gemstones

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