The most interesting category of coloured stones is gems that display optical phenomena. This week we will examine some of the more common phenomena that can add interest and profit to the coloured stone department of a retail store.
Phenomenal stones exhibit optical effects due to interaction with light. Opal is a good example. As the light moves, the colours of the opal move and change caused by light bending around the internal structures of the stone. Strong lively colours with unusual or attractive patterns can command a steep price and common opal, while still attractive, can be very reasonable. Some very good synthetic opals are in the market that are very pretty and durable. Some can even be cast in place. Synthetic opals need to be disclosed.
The same can be said about stones that display asterism, or stars. Microscopic needle crystals that are oriented along the crystalline axis of the stone cause the stars when illuminated by a single point light source. Star Ruby and Star Sapphire with a good, deep colour, good translucency, and a bright and sharp star can easily satisfy the most discriminating and wealthy client while lighter colours can make these fascinating stones affordable for almost any budget. Synthetic stars offer a beautiful look at an affordable price. Surface diffusion treatments can produce stars on lower quality stones as well. Both of these are decent options as long as there is proper disclosure.
Cat’s eye stones are caused in the same way as star stones but the needles are oriented on only one axis of the crystal. The most well known example is Cats Eye Chrysoberyl. A clean, honey coloured stone with a crisp, bright eye can be very valuable. Tourmaline, Alexandrite, Opal, Moonstone and Quartz are available with cat’s eye phenomena. In fact, many stones have the potential to produce an eye. Synthetics and treatments are readily available and, of course, need disclosure.
Stones that change colour under differing light sources are very popular right now and have been for over one hundred years. The rarest and most valuable is Alexandrite with a colour that changes from red or purple under incandescent light to green or bluish green in daylight. Very fine, clean Alexandrite with strong Red to Green colour change are usually priced higher than diamonds. The best come from Russia but they are extremely rare. Brazil produces very fine stones but supply seems to be getting thinner. Africa and India produce mostly commercial qualities but some nice gems do pop up. Colour-change can be found in Sapphire, Garnets, Diaspore and many other species but Alexandrite is the most desirable.
There are plenty of other interesting phenomenal stones, some very inexpensive and others that can be pricy. Having a section of your coloured stone department dedicated to phenomenal stones can set you apart from ordinary jewellers. They are great conversation starters and can enhance the perception that you are knowledgeable and different. But most importantly…they are just fun to have around!
