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Alexandrite
This extremely rare gemstone of fairly recent
history owes its name to the fact that it was first discovered
in the Urals in 1830, on the day of Prince Alexander of Russia's
coming of age.
Appearance Green: it can
be almost emerald-colored, but is more often yellowish or
brownish green. Its main characteristic is the ability to
change color if exposed to a light source rich in red rays;
by candlelight or tungsten light, it turns red or reddish.
This unusual phenomenon is what distinguishes it from other
green chrysoberyl. This pronounced color change from green
to red is highly prized and, as always, the exact tone of
the color, or colors, is important, the ideal being brilliant
green turning to fiery red, although dull green turning reddish
or slightly turbid blood red is more common, and given alexandrite's
extreme rarity, even stones with a number of inclusions are
cut. It is given an oval or round, mixed cut, or a rectangular,
step cut. Alexandrite is so rare that few people have ever
seen one; and perhaps for this reason, the name is applied
to other, mainly synthetic stones, not remotely like it (usually
violet-colored synthetic corundums).
Distinctive features The
changing color is an unmistakable characteristic. However,
in the last few years, small quantities of green or bluish-colored
grossular garnet that turn red like alexandrite have been
found in East Africa. To distinguish between the two, it is
useful to look for signs of birefringence, as garnet, unlike
alexandrite, is singly refractive. The refractive indices
of the two stones, on the other hand, are very similar, as
are their densities.
Occurrence Found in limited
quantities in the Soviet Union, Brazil, Sri Lanka, and some
East African countries (Zimbabwe and Tanzania).
Value Fine stones are extremely
valuable and on a par with emeralds, rubies, and sapphires.
When the colors are dullish, the value falls appreciably,
but because of its rarity, all alexandrite is expensive. It
is a collector's item.
Simulants and synthetics
Attempts have been made in the past to imitate alexandrite's
change in color using synthetic spinel and corundum, but the
results have been modest. More recently, a violet-colored
synthetic corundum has been widely marketed under the name
of alexandrite, despite its lack of any real similarity to
the natural stone. However, many who have never seen true
alexandrite apply the name to this synthetic corundum and
possibly for this reason, some manufacturers of synthetic
corundum call their violet stones alexandrite type. Synthetic
alexandrite has also recently been produced, but mainly for
industrial purposes. For the time being, therefore, synthetic
alexandrite is even rarer !han the natural variety.
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