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Alexandrite
Alexandrite is the birthstone for June. It also is used to commemorate the
45th and 55th wedding anniversaries. Alexandrite has been described as "an
Emerald by day and Ruby by night.
It is one of the few gemstones whose
color changes radically under different lights: green, blue-green or pale green
in daylight to mauve, violet-red or purplish in incandescent light. A member of
the mineral group Chrysoberyl, Alexandrite's color change is due to the
differential absorption of different wavelengths of light by trace amounts of
chromium. To the layman this means that the red and green are always present
but fighting for dominance. If there is more red in the ambient light (i.e.
candlelight or incandescent) the reddish nature of Alexandrite prevails.
Daylight and most fluorescent light has a greater predominance of blue, hence
an Alexandrite will appear bluish green. It is extremely rare to find just the
right trace amount of chromium in a natural stone to make this dramatic color
change possible, hence the high prices commanded by fine natural Alexandrite.
Stones over 5 carats are excruciatingly rare, especially
if the color change is
good. The largest known Alexandrite is a gorgeous 66 carat cut stone currently
on exhibit at The Smithsonian Institution.
This gem variety was given the name Alexandrite as it was discovered in 1830
"reportedly" on the same day Czar Alexander II came of age. The first
Alexandrites were found in Emerald mines on the right bank of the Takovaya
river in the Ural mountains about 57 miles north-east of Sverdlovsk (Ekaterinburg).
This location produced stones for a few decades then ran dry and was closed.
After that most "Alexs" on the market were from Brazil and Ceylon.
Due to recent political changes, some of the old mines have been re-opened and
found to produce! The Russian mining is limited to the summer months because of
the bitter weather and remote location. As Alexandrite was, at first, exclusive
to Russia and displayed their national military colors of green and red, it was
long held in very high esteem by Russian aristocrats and royalty.
It is important to note that Brazil produces excellent Alexandrite with a
strong color change.
Although Alexandrite has a high hardness number of 8 ˝ , some care must be
taken to avoid knocking it against hard surfaces. It should not be exposed to
excessive heat (such as a jewelers torch) as that could effect its color
change.
TREATMENT: No presently known treatment for Alexandrite.
MOHS HARDNESS: 8 ˝
CHEMICAL COMPOSITION: BeAl 2 O 4
REFRACTIVE INDEX: 1.746-1.755 (+/- .004 - .006)
(The angle light is bent traveling through a gemstone)
DENSITY (SPECIFIC GRAVITY): 3.71-3.73
(The number of times heavier a gemstone is compared to water)
PRINCIPAL SOURCES: Tanzania, Russia (Ural Mountains, Siberia), Brazil and Sri
Lanka (Ceylon)
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