By Luke Cairns
“All that we see or seem is but a dream within a dream.” – Edgar Allan Poe
In this job it is very easy to become accustomed to the extraordinary. Every day we are fortunate enough to handle some of the finest jewels mankind has ever made, incredible pieces that punctuate the most important moments of people’s lives; whether it be a gift given at the birth of a newborn, rings exchanged to signify a shared love, or a treasure chosen to commemorate a loved one, sorely missed.
Less frequently however, do we come across a phenomenon within the already phenomenal. I am of course referring to gemstone phenomena, as it is known, which encompasses a variety of optical effects that can be found in some of our most beloved gemstones. Mother nature’s mysterious charm dictates which gemstones will be touched by these magical properties. An array of visual characteristics that enhance the already beautiful gemstones, imbuing them with an added layer of wonder. These are asterism, chatoyancy, adularescence, play-of-colour, iridescence and colour-change.
“Oh, don’t let’s ask for the moon. We’ve already got the stars!” – Bette Davis
Asterism, or as it is more commonly known, the ‘star’ phenomenon, is one of the most sought-after optical effects that occur naturally in gemstones, with the most prized being those occurring in sapphires and rubies. Nevertheless, stars can also be found naturally in spinel, diopside, beryl and quartz. This captivating quality is caused by tiny needle-like inclusions known as ‘silk’ that, once exposed to bright light, will reflect the light in a burst of rays across the stone. When these stones are cut ‘en cabochon’, meaning a smooth, domed polish with no facets, the light can form four, six or very rarely up to twelve rays, all spreading from the centre of the stone. A famous example is the Star of India, a 563.35 carat milky-blue star sapphire that despite its name originated from Ceylon (modern day Sri Lanka), affectionately known as the ‘jewel box of the Indian Ocean’.
“Cats are connoisseurs of comfort.” – James Herriot
If astronomy is not your cup of tea, would a fascinating feline phenomenon take your fancy? Known in the industry as chatoyancy, the French word for ‘shining like a cat’s eye’, or ‘cat’s eye’ for short, it is an extraordinary optical effect that occurs when some gemstones, cut en cabochon, reflect a narrow line perpendicular to the observer’s line of sight. Much like asterism, this is caused by tubular or needle-like inclusions that are tightly packed in one direction throughout the stone. If the term ‘cat’s eye’ is used on its own, it will always be in reference to chrysoberyl, the most common gemstone to harbour this property. It does however occur in other gemstones such as tourmaline, beryl, demantoid garnet and quartz.
Adularescence is a phenomenon also caused by inclusions, however unlike our previous gemstones, no rays are formed. In this case the inclusions reflect light throughout the stone, creating a hazy glow just below the surface. Perhaps the most popular adularescent gem is the moonstone, celebrated for its bluish-white milky radiance.
Play-of-colour is a phenomenon that is only found in opals, which is, according to the Gemological Institute of America (GIA), the world’s most popular phenomenal gem. Play-of-colour refers to the flashes of colour exhibited by opals, which break up light into distinct spectral colours, caused by the grid-like structure of the stone. This can occur in many of the different varieties of opals—black, white, and fire opal, each named for the base colour of the stone. Some of the rarest and therefore more valuable opals are those which display all the colours of the rainbow, most notably red, against a black base colour.
Iridescence is the term for an object’s ability to change colour as it moves. Mother-of-pearl is one such substance which exhibits iridescence, as do iris and fire agates. Like opals, pearls also have their own phenomenon, a variant of iridescence, which is called orient. These organic gems typically have a base colour—most typically white or cream—as well as an over tone—such as pink, blue, purple, or green. Orient is the name given to a pearl with an iridescent or multicoloured overtone.
One of the most amazing gemmological phenomena, colour-change refers to gems which change colour in different types of light. The most famous of these is alexandrite chrysoberyl, which changes from reddish purple in incandescent light to bluish green in fluorescent light. Another gemstone with the ability to change colour are sapphires, which we are privileged to have within in our collection, including some incredible Ceylon varieties.
Exceptionally rare, some stones exhibit multiple phenomena. A number of star and cat’s eye gems—such as sapphire or alexandrite—can at the same time be colour-change. Whatever the effect or combinations thereof, phenomenal gemstones lend the jewels in which they are set an allure beyond the brilliance they already possess.
If you choose to opt for optical, if you have a preference for the phenomenal, if you want to experience the extraordinary, come and see us… You won’t be disappointed.
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