Opal
Mineral: Tectosilicate
Hardness: 5-6.5
Birthstone: October Anniversary: 14th
“The Rainbow Gem”
The name opal derives from the Greek Opallos, meaning "to see a
change (of color)” and from the ancient Sanskrit Upala meaning precious stone. There are many
different varieties of opals: Mexican red fiery opals, European and Czechoslovakian white opals
and several from Australia including red, blue, green and black.
In 1987, a miner working in the opal-rich town of Coober Pedy, Australia, stumbled across the
opal-covered fossil of a pliosaur within a mine. During the
fossilization process, opalization occurred, leaving the seven
foot long dinosaur fossil with a semi-precious, opalescent
sheen. Opalized fossils are formed mainly in white opal.
Paleontologists and gem dealers often struggle over who
should get the opalized Cretaceous marine reptiles and
dinosaurs found in Australia.
Opals are hard, hydrated silica. The process of precious opal
formation is not entirely clear. It is thought that opal starts out
as a concentrated silica gel that accumulates in cavities and spaces within a host rock,
eventually hardening into gemstones. Because of their high water content, opals are prone to
cracking. In fact, opalescence, the iridescent “play of color” characteristic of this stone, is the
result of light reflecting off of the tiny spherules which reflect different wavelengths of light.
White, yellow, blue and green are the most common colors seen through play of color, whereas
violet, fiery red and orange are the most valuable and sought
after of opal colors. Opals are opaque to transparent with a
soft waxy luster. They are very delicate and should only be
cleaned by wiping with a soft cloth.
The Opal’s reputed positive qualities were held until 1829
when Sir Walter Scott wrote his bestselling novel, Anne of
Geuerstein. In the story, a lady who was accused of being a
demon wore an opal in her hair. It flashed fiery red when she
was angry and sparkled beautifully when she was happy. She dies after holy water accidentally
falls on the opal and destroys its color. This story caused the opal market to crash until 1877
when the discovery of an amazing black opal was found on Lightening Ridge.
Opals are stones of inspiration which enhance imagination and creativity.
They can bring inspiration to projects and to life and Spirit. Its own spirit is
at times like that of a child, spontaneously playing, dashing color where
ever it pleases. Historically, the opal symbolized fidelity, assurance and
hope. In Rome, Caesars gave their wives opals for good luck as carrying
opals was believed to bring good fortune. This precious gem was said to be
included in the crown of the Holy Roman Emperor.
As mentioned, there are many different types of opals. The main commercial varieties are:
White Opal / Contra-Luz Opal: transparent to semitransparent, shows play of color best when
light is reflected through it.
Jelly Opal: also called water opal, no play of color.
Hydrophane Opal: only develops play of color when immersed
in liquid.
Fire Opal: transparent to translucent opals with warm body
colors of yellow, orange, orange-yellow or red. They do not
usually show any play of color, although occasionally a stone
will exhibit bright green flashes. The most famous source of fire
opals is the state of Queretaro in Mexico; these are commonly
referred to as Mexican Fire Opals. Fire opals are also found in
Central America, South America and the United States (Idaho
and Oregon).
Peruvian Opal: a semi-opaque to opaque blue-green stone found in Peru.
Pineapple Opal: also called Opal Pseudomorphs. These are a rare form of opal only found at
White Cliffs, New South Wales and are created by opal deposits in various fossils. Many of these
fossilized forms contain an exceptional quality of noble opal.
Boulder Opal: This type, composed of opal naturally
occurring on its host rock, is mined predominately in
Queensland, Australia. It is easily identified because when
cut the host (brown ironstone) is left on the back of the opal.
Black Opal: This opal is by far the most valuable and
appreciated of all opal varieties. Almost all black opals are
mined from Northern New South Wales and the majority of these are specifically from
Lightening Ridge. Despite the name, black opals can encompass a variety colors, top specimens
reflecting the full spectrum of color against a dark gray to black background.