Opalescence effects in Opal
by Nasrina Parvin Khan
The milky, turbid aspects of opal described as opalescence. This phenomenon has been seen in common opal or potch opal. These types of opal do not show a play of color.
There are various kinds of
special optical phenomenon, which
can be exhibit by the gems. Special
optic phenomenon is the unique
property of a gem that adds a
distinct identity character to the
gem. We can identify the gem with
Sometimes a particular type of gem
shows multiple special optical
phenomena, like opal.
We know opal for its play of color.
Except play of color, opal exhibits
another special optical phenomenon
Usually, people confused with two
special optical phenomena in opal.
But play of color and opalescence
are two different phenomenon of
The milky, turbid aspects of opal
described as opalescence. This
phenomenon has been seen in common
opal or potch opal. These types of
opal do not show a play of color.
The term 'opal' derives from the
Greek 'opallios', the Latin 'opalus'
and the Sanskrit 'upala' that means
The ranges of color in opal may vary
from colorless to white, milky blue,
gray, red, yellow, green, brown and
Opalescence - How it happen?
Opalescence is caused by the
reflection of short wavelength
light. Usually it occurs in the blue
spectrum. Due to this action of
light a milky blue, pearly
appearance occurs in opal which
known as opalescence.
The structural pattern of opal is
the reason of this special optical
phenomenon thus the reflection of
Opal is an amorphous form of silica
(SiO2, nH2O). It is made up of
sub-microscopic spheres of silica
with a little amount of water. Air
also trapped in the spaces between
these round spheres. The amount of
water in opal may 3% to 21%.
In case of common opal, the openings
between the spheres are
comparatively large. So, the light
doesn't have to bend when traveling
through them and no diffraction can
takes place. But the light scattered
instead of diffraction. The
scattering effect of light creates a
sort hazy effect in the inner
particles of opal, which is commonly
known as opalescence.
This phenomenon is best admired in a
flat cabochon-cut opal (a tall,
domed shape gem is called as
cabochon). The whole surface of opal
exhibits opalescence in this case.
We can divide opals in various types
according to the color and
opalescence type, such as i) white
opal with opalescence against the
pale gray or pale blue background,
ii) black opal with effective
opalescence and dark background,
iii) harlequin opal with spectacular
fancy opalescence outline against
different colors of mosaic figures,
iv) flaming opal of yellow or red
color with spectacular opalescence
consisted a fire.
Opalescence is the optical
phenomenon, which adds value to the
opal and helps the gem belong to the
Other Optical Effects in gemstones
Play of Color
Color Change phenomenon
Special Optic Phenomena