History & Introduction
Opal is the October birthstone. Opal gets its name from various languages: in Sanskrit
upala, meaning "precious stone", in Latin it is called opalus and in Greek it is
known as opallios, both meaning to see the change in color. The most interesting
characteristics of opal is the capacity to reflect as well as refract to a specific
wavelengths of light. Different wavelengths of light interplay and provides opal
a unique visual appeal, and create it one of the most desirable gemstones in the
world. It is one of the world's most beautiful and precious gemstone to be known.
The earliest known opal artifacts was discovered back from 4000 BC that came from
Ethiopia. These artifacts were discovered later in a cave in Kenya by famous archaeologist,
Louis Leakey. In the middle Ages, opal was taken as the stone that could provide
great luck because it was believed to possess all the virtues of each gemstone whose
color was represented in the color spectrum of the opal. It was even known to confer
the power of invisibility if wrapped in a fresh bay leaf and held in the hand. In
novel of Scott, the Baroness of Arnheim wears an opal talisman that possess supernatural
powers. On the talisman, when a drop of holy water falls, the stone becomes colorless
and thus soon the Baroness dies. With this people began to connect opals as bad
luck and death. This dropped the sale of opals in Europe in 1829 by 50%, and continued
to be low for the next twenty years or so.
Recognise - The concentration of opal is hydrated silicon dioxide
that contains from three to thirty percent water. The following feature along with
its relative softness with a rating of 5.5 to 6.5 makes opal quite easy to recognize
and discern from other gemstones. Not like the other gems with play of color or
iridescent effects, opal even shows 'opalescence'. Additional lustrous stones don’t
show this pearl-like bluish color effect that appears to glide across opal, however
in fact it will mainly display color, which will appear abruptly, disappear and
then reappear, it depends upon the viewing angle. In large number of cases, close
observance of color and optical phenomena can usually help distinguish opal from
many alike gemstones.
Availability - Gem Opal from Brazil, Polished opal from Yowah,
Queensland, Australia, Multi-Color solid black opal cabochon from Lightning Ridge,
NSW, and Australia produces around 97% of the world's opal. Coober Pedy in South
Australia is considered to be the primary source of opal.
Usages - Opal is one of the most precious gemstones, in which Black
Opal is the most valuable and desired form whereas White Opal and Precious Fire
Opal even is available expensive in the market. Opals gemstones are cut then polished
into cabochons, and in a few cases they are faceted into several cuts. Opal is one
of the popular stones among mineral collectors and museums compete to get the finest
specimens. There is no industrial or commercial use for Common Opal, except for
those specimens that are brightly fluorescent and are collected by fluorescent mineral
collectors.
Buying Guide
Color - Opal is available in various colors, which includes white,
colorless, pale yellow, pale red, grey, brown and black. Diffraction can cause flashes
of any color of the rainbow which can be seen in opal's color play. Yellow, blue
and green are commonly found colors whereas violet, red and orange are rare and
they are seen through play of color. Opalescence mainly comes in milky blue in color,
however it available in fewer colors. The saturation of the color of the body, the
play of color as well as the transparency determine an opal's value.
Clarity and Lustre - Opal gemstones are also available in transparent
to opaque. Materials that are from transparent to translucent are naturally more
valuable as compared to opaque materials. Mainly, all opal will have some visible
internal fractures or inclusions such as patches, potch (common opal) or matrix
rock inclusions. Opal tends to exhibit a wax to resinous luster which helps accentuate
play of color and opalescence. Stone that are fine as well as have a vitreous luster.
Cut and Shape - Opals are usually cut into shapes which maximize
and preserve the weight of the rough opal. They are often cut en cabochon and depending
on the opal color bar, it may be cut as per high or low domes in order to maximize
play of color and adularescence. Opal can also be faceted and is mainly seen with
'fire opal'. Opals can be found in various shapes, including traditional ovals,
rounds and cushions, as well as fancy hearts. Opal is often carved into ornaments.
Treatment - Though opal is typically untreated, however it is impregnated
with wax, oil or even plastic to improve the color along with stability. It may
also be layered (as in doublets or triplets) in case of durability. Treatments method
of 'Smoking' currently are more common as before. The method of 'Smoking' is done
to darken the color of the body. There are forms of synthesized opal available.
Technically they are 'imitation opal' as they often include substances such as plastic
that are not found in natural opal.
Gemological Characteristics: