|
Aquamarine
The name refers to the palish blue, light blue-green
or even light green variety of beryl. The green of aquamarine
is a watery green without any trace of yellow and is due to
iron, not chromium, as can be seen from examination with a
gemological spectroscope.
Appearance The most valuable
color is a rich, sky blue; but because the stone is pleochroic,
even the blue stones have a green or greenish-blue tinge in
one direction. Quite large stones, ranging from several carats
to more than ten or a few tens of carats, are relatively common.
Many are virtually free of inclusions. (Again, where there
is plenty of material available, poor quality specimens do
not usually come to market.) The luster is vitreous and not
exceptional. The most common cut is the emerald type, although
mixed oval or pear-shaped cuts are not infrequent.
Distinctive features The color
of this stone, combined with its particular type of pleochroism
and vitreous luster, distinguishes it fairly easily from blue
topaz and light-blue synthetic spinel, the first being a definite
blue color, the second having a gray or violet tinge, much
stronger luster and no pleochroism.
Occurrence Most aquamarine
comes from the pegmatites of Brazil, where crystals weighing
several kilos have been found. Other deposits are in the Soviet
Union (Transbaikalia, Urals, and Siberia), Madagascar, the
United States, and, recently, Afghanistan.
Value Rich blue stones several
carats in weight are among the most valuable of secondary
gems. They are worth a lot more, for instance, than blue topaz
of similar characteristics. Pale or green stones are much
less valuable.
Simulants and synthetics Aquamarine
is imitated by blue glass, which faithfully reproduces the
color, if not the pleochroism, but it is most often imitated
by blue synthetic spinel, of a slightly different color, with
superior luster and no pleochroism. Because of the general
similarity, this is sometimes called synthetic aquamarine,
although the latter, as such, is not produced. Light green
or yellow-green beryl can be turned blue by heating it to
a certain temperature for a certain length of time. This practice
has been in use for several decades and is considered acceptable,
as with zircon and sapphire.
.
|
