Special Optic Phenomena in Gems @ Jewel Info 4 UBy: Nasrina Parvin Khan
It is said, "jewelry is the best
friend of a woman". Yes, jewelry can
increase the confidence level of a
woman as a beauty wear as well as
wealth. Designs of jewelries changed
with time but the value remain
unchanged.
In the present scenario, gemstone
jewelries take a distinct place
among the women because of its
stunning beauty and the myth "it may
brings good luck". The glitz and
glitter of a single gemstone can
lights up the face and enhance the
radiance of a woman's persona. Gems
allowed the light to pass through
its. This effect enhances its color
and brightness and creates an
enchanting look.
The beauty of gems justifies
with its color, luster,
brightness, brilliance,
scintillation and dispersion.
Optical properties are
responsible to create all this
qualities of a gem. These are
also important to identify
gemstones.
But the most important feature
of gems is the special optic
phenomena. Special optic effects
exhibit in some gems is called
as phenomena. These uncommon and
excellent effects very often add
value to gems.
Special optic phenomenon
Special optic phenomenon is a
particular property of
transmitting or reflecting
light. The structure or
inclusions of a mineral such as
gem is the reason of this
property.
Asterism,
chatoyancy,
play-of-color,
opalescence,
labradorscene,
adularescence and
color change are some special
optic phenomena which have been
seen in gems.
Asterism is one of most
important special optic
phenomena, which has been seen
in sapphires, rubies, rose
quartz and some other gems. The
term "Asterism" came from the
Greek word "aster", which means
star. From the name we can
easily guess, "asterism" is star
shaped light effect across the
surface of a gem. Asterism is
caused by dense inclusions of
tiny fibers in the mineral. This
inclusion is the cause of the
reflection of light and forms a
wavy star like formation, which
moves around when the mineral is
rotated. The star may have four
or more rays depending on the
crystal system of the gems.
Asterism is best seen when a gem
is cut as a cabochon. This optic
phenomenon is most visible in
direct light. There are two
types of asterism. Like,
Epiasterism which has seen in
sapphires and most other gems
and Diasterism which has seen in
rose quartz.
Chatoyancy is another special
optic phenomenon. This
phenomenon is also known as
Cat's Eye effect. Because the
reflection exhibits a single
bright band of light across the
surface of a gemstone and forms
a Cat's eye. The eye can be seen
at right angles. Inclusions of
bundles of parallel particles of
fibres of another mineral inside
the gems are the reason of silky
radiance of gems, which called
Chatoyancy. This phenomenon is
commonly seen in Chrysoberyl,
Tourmaline, and Tigers Eye and
very rarely seen in Emerald,
which come from Brazil and
Colombia.
Chatoyancy or Cat's eye is best
esteemed under sunlight or some
other point light source. Each
of multiple light sources
produce a Cat's Eye on the gems
and give an unfocused look. In a
cloudy day or under fluorescent
lights Chatoyancy or Cat's Eye
may vanish completely. Usually
it is seen on a round shaped
stone, which called, as
cabochon.
One of the common special optic
phenomena is Play-of-Color. The
iridescent color effects in Opal
and several gems described as
Play-of-Color. Opal is made of
sub-microscopic silica spheres,
which is the cause of light
diffraction from the surface or
the interior of gems. This
property helps to produce
different colors as the angle of
incident light changes. The
colors we see depend on the
sizes of the spheres.
There are four terms to describe
the various kinds of
Play-of-Color. A tiny close-set
patch of color is called
Pinfire, whereas a big, angular
close-set patch of is called
mosaic. Sweeping reddish bands
across the stone is called
Flame, whereas blue and green
color effect is called as
Peacock.
Alexandrite effect
Color change is a distinct optic
phenomenon, which has been seen
in several gems. Alexandrite is
the best example for showing
Color change effect. For this
reason sometimes it referred as
Alexandrite effect. This
phenomenon is also found in
sapphires and Garnet. Gems
distinctly change their color
under different lighting source
because of its color change
effect.
Opalescence,
Labradorescence,
Adularescence are some other
special optic phenomena which
have seen in several gems.
Opalescence is an optic
phenomenon, which is commonly
seen in opal. The milky aspect
of opal described as
opalescence.
Labradorescence is an optic
effect, which is commonly seen
in labradorite. Gems change
color because o9f its position
with blue reflection for this
effect.
Adularescence is most commonly
seen in moonstone. This
phenomenon creates a milky
radiance or wavy light effect in
gems. Inclusions of microscopic
particles or irregularities of
structure of transparent to
translucent gems is the cause of
blue reflection, which known as
adularescence.
It is the fact that special
optic phenomena are the reason
to create distinct property and
attractiveness to a gem and add
value.
See pictures of optic phenomena
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