Alexandrite - Chrysoberyl

What to look for in Alexandrite?

First and foremost, we need to look at the quality and strength of the color change. A strong change where the colors are bright and attractive under any kind of light is most desirable. Many stones are either a beautiful green in daylight or a nice pinkish red under incandescent light but they are less often attractive under both light conditions. However, since alexandrite is so rare, even stones with a weaker or a less attractive change are still valuable. We grade color changes as faint, weak, moderate, or strong.

Clarity, cut, and size are the next most important considerations after color. Large stones are always rare and as a result more valuable. Cutting and proportions are important but a careful balance between weight retention, shape, color change and, careful positioning of unremovable inclusions is required to produce the most valuable stone. A poorly cut 1ct.+ stone may be worth more than a perfectly cut .90ct. stone so cutting and performing require careful attention in order to maximize yield and value.

Which Alexandrites are best?

Although Russian Alexandrites have the most historical value, fine stones are available from several other deposits. Brazil, India, and Tanzania produce the bulk of today’s production but Alexandrites are also found in Sri Lanka and Madagascar. Top stones are extremely rare but all of these deposits occasionally produce exceptional stones. Brazilian stones typically show the best reds under incandescent light but Indian stones are well known for their superior bluish green daylight colors. Tanzania and Madagascar seem to produce the largest stones and some of the stones are exceptional. There is currently hardly any production of Russian stones. What causes the color change?

Alexandrite is a trichroic gemstone which may absorb and reflect light differently in each of its three optical directions. However, it is not the trichroism that is responsible for the remarkable change. The color change phenomena is a result of the presence of chromium +3 ions and the way they are absorbed and reflected. In rubies the chromium absorption band is around 550 nanometers and in emeralds, the band is around 600nm. In alexandrite, where the band is at 580nm and right between ruby red and green emerald, the stone is balanced between them. When the light is balanced (daylight), the stone will be green but when the light source is reddish (incandescent), the stone appears red.

Alexandrite or Chrysoberyl, What's the difference?

In practice, chrysoberyl and alexandrite may be difficult to differentiate. Since stones with a weak change may be called alexandrite and stones with a faint change are called chrysoberyl, what is the difference? Where is the borderline?

Since the origin of the color change in alexandrite is due to the presence of chromium while the color of yellow or brown chrysoberyl is due to the presence of iron, a close examination of the spectroscopy will reveal the differences as both chromium and iron display characteristic spectrums. The yellow variety shows a broad band centered at about 4450 A in the blue violet while the alexandrite variety shows a chromium spectrum. The presence of chromium lines in the red orange area of the spectrum are diagnostic for alexandrite.

Fluorescence is another property to help us differentiate. Chrysoberyl owns its yellowish color to iron and usually shows no fluorescence. The red fluorescence of alexandrite can be observed using the “crossed filter” method and it has been inferred that in border line cases the presence of a red glow and a faint chromium spectrum absorption spectrum would prove the stone to be alexandrite and not chrysoberyl.

Alexandrite is an uncomplicated stone to wear. The more distinct the change of color the more valuable the stone. Alexandrite is a stone for experts, enthusiasts and connoisseurs. Its uniqueness and high value are not evident at first sight as the mysterious color change in alexandrite will only occur on exposure to different light sources. But if you really get involved with alexandrite you will be utterly fascinated by this gem. Maybe you will also feel some of the mysterious magic and lore ascribed to it. Alexandrite considered a very good omen. In critical situations it is supposed to strengthen the wearer’s intuition and thus help him or her find new ways forward in situations where logic will not provide an answer. Alexandrite is also reputed to aid creativity and inspire imagination. We at AJS hope you enjoy your Alex whatever color it is...