|
Blue zircon starlite
This does not appear to have been known for
long, parti. because it is often (but not always) obtained
by heat treat ment of other colored zircons, which is standard
practice commercially. The name starlite is not universally
ac cepted.
Appearance The best color (not often seen)
is a lighv electric blue not found in any other gem, with
pleochroisrmaking it look greenish in one direction. It can
also be sky blue with less obvious pleochroism, a very soft,
pale bluc or a distinctly greenish light blue. It is usually
given a zir con-type brilliant cut, which is not always round;
also use are rectangular or square, step cuts. Mixed cuts
are les, frequent. The strong luster is shown to best advantage
b. the zircon cut and is less obvious in the step cut. Untortr,
nately, the brittleness of zircon often results in the edgebeing
slightly damaged and not clear-cut.
Distinctive features The marked
birefringence char acteristic of most zircons is easily seen
with a lens an will distinguish blue zircon from other stones
of a similn color. With a little experience (which is not
easy to com, by, as this is not a common gem), the color can
be seen t be quite distinctive, particularly the electric
blue. Blue zircon has the physical properties of high zircon,
hence tha refractive indices are not easily measured, but
it nearly a ways has a highly characteristic absorption spectrum.
Occurrence Blue zircons come
from Cambodia, Viet nam, and Thailand, where they are cut
(and, perhaps treated). All stones are therefore sold as if
coming fror Thailand.
Value The best quality, electric-blue stones, which arr relatively
uncommon, but not in great demand because no widely known,
are worth slightly less than the top second ary gems. Weak
blue or blue-green stones are worth a less.
Simulants and synthetics The
greenish-blue variety ha~ been imitated by synthetic spinel,
which is not, however birefringent. This gem is not manufactured
synthetically
|
