Los Angeles gem dealer with a specialty for rare gemstones, Evan Caplan shared his passion for Alexandrite with the DCGIA Members. Alexandrite one of the birthstones for June, is a very rare color-change variety of the mineral chrysoberyl. Green in daylight and Red in artificial light, color-changing Alexandrite is nature’s magic trick.
Alexandrite was named after its discovery in the Russian Ural Mountains in 1830 on the twelfth birthday of the Russian Crown Prince Alexander II, originally identified by the Finnish mineralogist Nils Gustaf Nordenskiöld.
Ordinary Chrysoberyl is yellowish-green and transparent to translucent. The three main varieties of Chrysoberyl are ordinary yellow-to-green Chrysoberyl, cat’s eye or Cymophane, and Alexandrite.
MINERAL: Chrysoberyl – CHEMISTRY: Be Al2 O4
COLOR: Bluish green in daylight, purplish red in incandescent light
REFRACTIVE INDEX: 1.746 to 1.755
BIREFRINGENCE: 0.008 to 0.010
SPECIFIC GRAVITY: 3.73
MOHS HARDNESS: 8.5
Assess fine Alexandrite by the extent of the color change and clarity it displays and by the quality of the red and green hues shown under different lighting conditions. Alexandrite should have a high level of transparency, a good appearance, and no eye-visible imperfections, gem-quality Alexandrite shows an attractive green or blue-green under sunlight, distinctly changing to a purplish red under incandescent light. Less-desirable stones may have daylight colors of yellowish or brownish-green and incandescent colors of brownish-red.
Cymophane is popularly known as “cat’s eye”. Chatoyancy arises from the fibrous inclusions or cavities within Chrysoberyl, cut as a cabochon, a silky band of light extends across the surface of the stone. Cats eye seen in Alexandrite is very rare, a real collector’s gemstone.
Fine-quality Alexandrite (extremely rare) has a green to bluish-green color in daylight, changing to a red to purplish-red color in incandescent light. Go to GIA for a great picture of Alexandrite.
Brown component in Alexandrite is the kiss of death as it greatly reduces the value of the gemstone. Sometimes you see a change from Brown to Browner – that is a color change you do not want to see. Go to GIA for a great picture of Good and Bad Quality Alexandrite.
Gem labs report color, but color classifications vary widely from lab to lab and can be disadvantageous to the perceived value. Too often consumers are buying the paper rather than the stone, so dealers are held hostage by the lab reports. Sending a gemstone to multiple gem labs will often leave you wondering what color is it?
So what do some people do? Throw out the reports that provided inferior color descriptions? Since each lab has their own specification for viewing and light source use, none share the actual specifications being used. While they all say a standard is necessary and many different associations have working groups that are trying to establish standards, no real movement towards a common Alexandrite specification has been made.
Alexandrite is found in the Russian Urals, Brazil, Sri Lanka, India and East Africa, although many mines are no longer producing, and the size of rough is smaller than in the past. With 3 out of a 1,000 gemstones of fine gem quality coming out of the Irissa mine in India. Most of the current material contains many inclusions, with limited production of fine gem quality material.
Evan shared photos and stories of many of his gemstone finds from Russia, Brazil, Tanzania and Sri Lanka. As well as information on the Minas Gerais mines in Brazil.
Find stones on the surface as they do not dig pits. Current mining is going through the trailings left from earlier excavation, which tends to provide mostly smaller carat stones.
Russian reputation although it has nice color change is typically not fine gem quality as it is highly occluded. Sri Lanka Alexandrite from the murisa mines. Tanzinia also has some great material. Brazil is where the best material has originated from in recent times.
Alexandrite of over 5 carats with a beautiful green and red color is extremely rare and valuable. Most fashioned Alexandrite is small, weighing less than one carat. Larger sizes and better qualities rise in price dramatically.
Quality cut gemstones seldom come from India & Africa, but Brazil often provides the best cut stones since they are sent to Hong Kong for cutting prior to sale.
Alexandrite is typically untreated, but imitation stones do exist. Occasionally, Alexandrite may be oiled, but this is not very common, and oil is likely left over from the polishing process. Many Alexandrites are synthetic (lab-grown) and others may be natural ‘simulated’ gemstones, such as color change garnet, sapphire or spinel. Many lab-grown (synthetic) alexandrite is actually corundum (ruby/sapphire) that has been laced or infused with either chromium or vanadium to provide the color. It is very expensive to create synthetic alexandrite, so even lab-grown stones can be very costly. Synthetic alexandrite has been available on the market since the 1960s.
Inclusions may be veils, needles and other natural crystal inclusions, better seen under magnification. Look for tiny crystals that look like black spots in the interior of the gem, veil like silky threads throughout a the whole or portion of the gem, or even what may look like tiny elongated tubes.
DCGIA thanks Evan for sharing both his knowledge and passion for Alexandrite with us!
Summary by Charles Marts