Distinguished by its characteristic play of light, the moonstone owes its name to a mysterious shimmer which changes appearance according to the angle from which the surface is viewed. This shimmer (schiller in technical terms) is known in as adularescence. Along with Pearl it is also the birthstone for the month of June.
This gem was very popular in the Art Nouveau era. Famous jewelry houses like Cartier’s and Tiffany’s used moonstone in their creations frequently and this was the main reason for the gem’s popularity. These gems were also seen in Roman jewelry used in AD 100 and in Oriental adornments belonging to the period before AD 100.
This gem is also known as ‘chandarkant’ meaning moon like. In India, this gemstone was considered scared and held special significance for lovers. Moonstone is also regarded as a dream stone that brings beautiful visions at night to the wearer. In some parts of the world the gem was believed to bring reconciliation amongst lovers and in other parts it was believed to drive sleepiness away. In Arabic countries, it is considered a symbol of fertility and women often wear this gem sewn out of sight into their garments.
Moonstone is a potassium aluminium silicate (K2O Al 2 O3 6 SiO2). It’s specific gravity is 2.56 to 2.59 and refractive index range is between 1.52-1.53 and 1.53 –1.54. Its hardness on Mohs scale is 6.
Moonstone belongs to the feldspar group. It is the best known gem variety of the feldspar mineral group.
The characteristic that renders the moonstone popular is ‘adularescence’. By virtue of what is termed as adularescence a gem displays a billowy floating light which appears to come from below the surface. The term ‘shiller’ or ‘schiller’ is often used to describe this kind of light.
In moonstone, adularescence is due to a layer effect, where thin inner strata of two types of feldspar intermix. These layers scatter light either equally in all spectral regions producing a schiller. The word adularescence is derived from the word ‘adularia’ which was name used for this gemstone before it came to be known as moonstone. The word adularia comes from the very first source of moonstone that is the Mt. Adular in Switzerland.
The most valuable moonstone is the one that displays colorless, semi-transparent to transparent appearance, without visible inclusions and a vivid blue adularescence. Such a fine quality gem will have a glassy purity with a mobile, electric blue sheen.
The gem has to be cut in a dome shape, also know as cabochon cut to display its adularescence well. This gemstone is also cut and faceted into beads. Many times it is also custom cut as seen in the figure.
Moonstone of sizes ranging from 1 carat to several carats are easily available.
The most well known inclusions found in a moonstone are the tiny tension cracks called centipedes-like inclusions, which resemble the many-legged creature. Of all the gemstones only this gem is known to have centipede-like inclusions, hence the price will go up with the presence of this beautiful inclusion in a moonstone.
There are three main factors that play a role in the price of this gemstone; namely the body color, sheen or adularescence color and orientation of the sheen. The body color of the stone should be colorless, the adularescence blue and the sheen centered to the top of the gem. Such a fine quality gem many fetch a high price in the market. With any difference in the above factors will cause the price of the gem to drop. This specially cut and carved moonstone ring is sold on ebay for around US$15.
Blue moonstones are beautifully used in moonstone jewelry like moonstone rings, moonstone earrings, moonstone bracelets and moonstone necklaces. It is also sold in the market as moonstone beads for around 10US$ per line.
Traditionally, Sri Lanka was known to produce the finest moonstones which were almost transparent, with a bluish shimmer. Today, besides Sir Lanka it is also mined in Switzerland, India, Russia, Brazil, Australia, Madagascar, USA and Burma (now Myanmar).
The gemstones that are closest in appearance to the moonstone are chalcedony, fibrolite and heat-treated synthetic white spinel. Although these simulants of moonstone most of them are nearly the same price or even more valuable that the moonstone. In conclusion, there is a rare chance to be cheated with a simulant when buying this gem.
Heat and irradiation are the most common treatments carried out on moonstone.
Moonstone is the official state gem of Florida, USA.
Moonstone which exhibits iridescent flashes of blue, red, gold, green and white is called as rainbow moonstone.
Along with Pearl, Moonstone gem is also the birthstone for the people born in the month of June. Hence it is also called as june birthstone.
2) Gemmology by Peter G.Read
3) Handbook of Gem Identification - Richard T.Liddicoat, jr
4) Gems and Crystals - From the American Museum of Natural History - Anna S.Sofianides and George E.Harlow.
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