Beautiful blue zircon gained popularity
after its sudden appearance on
the world market in the 1920s.
The blue zircon ring in the photograph
below is a piece from that period.
In Thailand, brown zircons were
packed in charcoal and heated,
making it possible to change
them to a blue color not seen
before.
Since the late 18th century, colorless
and very light yellow zircons have
been mined in Matara, located in
the south of the island of Sri Lanka
(formerly Ceylon). There were called "Matara
diamonds," in reference to the
low-quality diamonds they resembled.
In Precious Stones (1896), Max Bauer
wrote that transparent yellowish-red
zircons were called "hyacinth," though
they were not popular. At the time,
almost all zircons were being mined
from the alluvial deposits of Ceylon
along with spinel, sapphire, and
cat's-eye chrysoberyl. A gem that
occurs in many colors, zircon's current
major source is Sri Lanka, followed
by Cambodia and Thailand.
Zircon is strongly doubly refractive,
meaning that light entering it is
split into two beams. Looking at
the photograph to the next
page,
one can notice how the facet junctions
seen on the far side through the
gemstone are doubled, appearing as
two lines. This effect is about twice
as strong in zircon as it is in peridot. |
The doubling
effect is more pronounced in thicker
stones, but it depends on the direction
of observation. The presence of such
doubling can assist in the separation
of singly refractive gemstones, which
do not split light, from doubly refractive
gems. Furthermore, the degree of
doubling seen under magnification
can be used as a reference in distinguishing
between various doubly refractive
gemstones.
Blue zircon's color will fade to
about half its overall depth when
exposed to direct sunlight for an
hour or so. If kept in a dark place
such as a safe, however, its blue
color will return. The day after
its exposure to sunlight, the color
will still be about 10 to 20 percent
faded, but within a few days its
original beautiful color will be
fully restored.
Blue zircon is slightly harder than
quartz at 7 but chips easily, so
durability must be considered when
using it in a ring. This gemstone
will maintain its beauty longer when
set in a pendant or brooch, where
it is less likely to be damaged. |
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