You may think these are just gems that are cool, and they are! This also refers to actual gemstones that a unique optical effects-phenomena. Some gemstones only exhibit phenomena in rare cases, where as others such as Alexandrite is almost always in this state and the gemstone itself is rare.
There are several types of Phenomena as it is called chatoyancy, color change, asterism and adularescence.
Chrsysoberyl from the Greek word “chrysos” meaning “a gold white spar” is the variety containing both of the most sought after of the phenomenal gemstones Cat’s Eye and Alexandrite.
Cat’s Eye Chrysoberyl displays chatoyancy, the word is coined from the French “œil de chat” and refers to the opening and closing effect of the “eye” of this stone.
A beautiful specimen of Cat’s Eye Chrysoberyl.
Color change is a unique phenomena occurring in only a small handful of stones one of them being Alexandrite, another member of the chrysoberyl family. This stones unique chemical properties make the color change depending on the nature of the lighting. “Emerald by day, Ruby by night” is sometimes said of this stone. Alexandrite’s color change is the result of small scale replacement of aluminum by chromium ions in the crystal structure.
Alexandrite “Emerald by day, Ruby by night”
Asterism is a beautiful effect in the stone that appears to the eye as a luminous star when the stone is polished into a cabochon. The most common gemstone to do this is the Star Sapphire, usually a grayish blue color and milky to translucent; this effect in Sapphire is caused by titanium dioxide impurities (rutile) present in them.
An exquisite Star Ruby, this occurrence is far more rare in Ruby from some reason so they are often given Ruby status even if they are more purple in color than a traditional Ruby, this on though is exceptional.
Adularescence is another beautiful optical phenomenon; and it appears only in the prescience of light. Like Asterism, adularescence is the product of the interaction between the light and the internal microstructures of the mineral and it not a chemical property of the mineral itself. The most common gemstone to see this with is the Moonstone, a bluish milky luster appearing just beneath the surface of the stone. It also appears in Rose Quartz, Opal and Agate.
Late 19th Century Victorian Cabachon Moonstone ring and rose cut Diamonds.
A very similar phenomena to adularescence is labradorescence, it also is the result of light refracting within the intergrowths of the material not of chemistry. This is the effect seen in the grayish-blue stone Labradorite.
A beautiful Labradorite speciman.
Of course there are many more stones that display phenomenal characteristics, check back in from time to time as these listings are updated.
Written by staff Gemologists at http://zeexchange.com/ if you are interested in any of these items in the article for purchase, please contact us at info@zeexchange.com.
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