Colorless, white, black, orange and yellow.
Moderate, wear with care
Australia, Brazil, United States, and other locations
Louis Leakey found six-thousand year old opal
artifacts in a cave in Kenya!
Grading and Classification
2000, The Australian Gemstone Industry Council established nomenclature and classification standards
for all types and origins of opals, This classification
has been adopted internationally.
Opals can be broken down into 2 basic categories:
Precious Opal : any opal displaying play-of-color. This phenomenon is
caused by the diffraction of white light thru a microscopic,
orderly arrangement of silica spheres. This category
includes white, black and boulder opal. Precious opal
can be further distinguished by types:
1: A single, solid piece of precious opal,
having a uniform appearance and composition. This is
the type of opal most commonly used for jewelry
Type 2:Precious opal that is attached
to its host rock (a non-opal) in the form of a layer
or seam. Boulder opal is an example of this. The opal
is attached to a brown, iron-stained sandstone.
Type 3: Matrix opal occurs when precious
opal fills cracks and openings in the host rock. The
opal forms in pre-existing clay or sandstone. This material
is frequently dyed.
Doublets & Triplets: These assembled
stones are not considered natural opals, although they
do contain a layer of natural opal.
Opal or Potch : These are varieties
of opal that do not show a play-of-color. Although they
share the same chemical composition as precious opal,
the silica spheres they contain are randomly arranged.
Judge the body color of an opal "face up".
If an opal has very dark potch on the back, giving it
the appearance of N5, it should be graded as N5.
can vary in degrees of transparency from transparent
to opaque. When an opal is transparent or semi-transparent
it is referred to "crystal". This is true
regardless of the body tone. "Crystal" refers
to the glass-like appearance of the gem, NOT a crystalline
with aniline dye, silver nitrate or sugar carbonized
with oil, wax, or plastic.
with black plastic.
with foil, black paint or laquer.
is a hydrous, silicon dioxide. It is unlike other
minerals because it is not crystalline! It is considered
to be a hardened jelly. It's water content varies
from about 2 to 21% mineralogically, but about 6 to
10% in gem opals. Gem opals are those with a play
of color and/or transparent orange varieties. The
varieties of gem opal are as follows:
or white body color with play of color
gray, dark blue or green body color with play of
|| Transparent or translucent orange or red, with or
without play of color
|| Colorless, transparent variety with play of color
play of color, or fire can be described as follows:
small points of fire
flashes of color that disappear when the stone is
angular patterns,like the diamonds in a harlequin
have a rather bad reputation, stemming from the plot
of a popular Sir Walter Scott novel in the 19th century.
The heroine of the novel has her life force caught
in the beautiful opal she wears in her hair and she
dies when the fire in the opal is extinguished. Opal
was also treasured in the Middle Ages and was called
ophthalmios, or eye stone, due to a widespread belief
that it was beneficial to eyesight. Blonde women wore
opal necklaces to protect their hair from losing its
color. Some thought the opal's effect on sight could
render the wearer invisible. They were popular talimans
for theives. According to aboriginal legend, opals
are devils, half-serpent, half-human, who lurk in
holes in the ground, luring men to their destruction
with flashes of magic. All that being said, I must
add, that I have owned, worn, cut and collected opals
since I was a teenager, with no apparent ill effects.