Rainbow Moonstone Blue Labradorite Feldspar. 

You will receive one piece of crystal, the total weight of the piece will be at least the amount quoted in the variation.

There is debate over what to call this mineral so I've reproduced this short article by Gary Roskin....

Okay, so it is, and it isn't. Yes, it is labradorite. No, it isn't really the mineralogically true "moonstone," although that doesn't keep most of the jewellery trade from calling it that. The proper varietal moonstone is an orthoclase feldspar, so the labradorite feldspar's so-called variety "blue rainbow moonstone" isn't too far from the correct branch of the family tree. The difference between labradorite "moonstone" and orthoclase moonstone isn't obvious, which results in the name-calling and mineralogical confusion among dealers and gemologists. Technically, "blue rainbow moonstone" is a misnomer, but a very popular one.

History and romance. The original moonstone—orthoclase moonstone, the one jewelers and consumers are most familiar with—is a translucent to semitransparent cabochon-cut gem with a white or blue billowy light. It can be white, orange, brown, or gray. You can find a fair number of orthoclase moonstones carved into moon-faced cabochons.

Because of its moving internal light, some wearers in the East believe moonstone has a living spirit within, one that will bring good fortune. It's considered a sacred stone that gives the wearer the power to read the future. Along with alexandrite, orthoclase moonstone is pearl's alternate birthstone for the month of June.

Fifteen years ago, a new "moonstone" came onto the market. It was discovered in southern India in a small mining area amid rice fields. (Orthoclase moonstones come from Sri Lanka as well as India, Burma, Madagascar, and other countries.) This discovery—which has been identified chemically as labradorite feldspar—has either a blue sheen, called royal blue in the trade, or a multicolored sheen, which the trade calls "rainbow."

Dr. Henry Hänni of the Swiss Gemmological Institute (SSEF) in Basel was the first to publish the chemistry and identification of the new "moonstones." Mineralogically, Hänni argues, these gems are not true moonstones, since the billowy light doesn't come from reflections off albite inclusions, as is the case with the orthoclase moonstone. The labradorite moonstone gets its effect by reflection off twinning planes, a common optical phenomenon of most transparent to translucent labradorites. This is the same phenomenon responsible for the colorful look of multicolored opaque to semitranslucent spectralight labradorite from Finland. Spectralight, as well as the traditional labradorite from Labrador—both commonly seen as huge tablets used for walls and countertops—get their dark gray body color from ilmenite inclusions. Labradorite moonstones do not contain ilmenite and therefore look like the milky orthoclase moonstone. Hence the confusion: It looks like moonstone but has the colors of labradorite.

"People who use the term 'labradorite moonstone' or 'rainbow moonstone' are on a 'red emerald' track," says Hänni. "The historical and global agreement of the term 'moonstone' is used only for orthoclase. Labradorite is not a moonstone."

Moonstone is a potassium sodium feldspar. Gemologically, it has a lower refractive index and lower specific gravity than labradorite. Blue and white are the only colors for a moonstone's sheen—there is no yellow, orange, or purple.

Labradorite, on the other hand, is a calcium sodium feldspar. It's also called spectrolite because it produces spectral colors. These colors are produced by interference and diffraction off labradorite's peculiar lamellar (flat plate-like) growth, not by scattering off albite inclusions. Labradorite has a higher RI and SG than orthoclase moonstone.

"The composition, identification values, and the reason for the light effect are different between moonstone and labradorite," says Hänni. "There is no reason—except commercial—to call labradorite a moonstone … it's confusing, and incorrect."

(Note: The Gemological Institute of America's Gem Trade Laboratory acknowledges the trade's use of the misnomer by making its identification conclusion as "Labradorite—known in the trade as rainbow moonstone.")

Qualities. It's difficult to find good clean pieces of blue rainbow moonstone. "In large sizes especially, it's hard to come by," says Manu Nichani of Blue Moon Enterprises in Carlsbad, Calif. "Quality becomes a big factor for anything larger than 10-by-12 ovals. The material tends to be highly included."

But inclusions are what cause the rainbow effect. "Inclusions break up the light, and we have spectral colors," says Nichani. "When there are more inclusions, that's when the rainbow effect comes into play." Fewer inclusions mean fewer colors. "Nice and clean, transparent to translucent, good clarity—that's when the stone is blue."

Color variations. Royal blue appears to be the most popular color, and today it's the "darling stone" of the designer trade. "It used to be a healy-feely stone," says Nichani. "Now, it's set with platinum and diamonds."

When it was first reported in the 1960s, rainbow moonstone was incorrectly labeled "water opal" because of its transparency and multicolor sheen. While there is material that shows just one or two colors in translucent cabochons, semitransparency with numerous different colors of sheen distributed evenly across the stone is preferred.

You will receive one piece of crystal, the total weight of the piece will be at least the amount quoted in the variation.

Each piece has it's own unique shape and internal markings, for this reason the item received may differ slightly from those shown in the photograph.