The Wonderful World of Color PT.9: Opal

Rain is one of the most beautiful gifts that we have been blessed with. Rain provides life to anything it touches; it gives kids a chance to jump in the puddles it forms, some people just close their eyes and listen to the gentle sound it creates on a roof. In the gemological world it begins the process of formation for one of the most amazing gems that exists.  This month we will take a closer look at Opal.

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Origins

Opal’s unique display of colors, lead the Romans to believe that it was the most precious and powerful of all gems. To them it symbolized love and hope, that is why the Romans would give Opals to their loved ones. As providence would have it, the Romans gave Opal its name from the word “opalus” which means “precious stone.” Many Arabic nomads believed that Opal contained lightning within them as they fell from the sky during thunderstorms and they wore them as protective tokens. In the middle ages, Opals were a symbol of hope, purity, and truth; many maidens had jewelry pieces adorned with Opals and Pearls to symbolize their purity. One of the most known lore about Opal is that anyone who’s birthday is not in October will have bad luck if they wear them. This myth dates back to 1829 when author Sir Walter Scott published Anne of Geierstein. The main female character in the story wore an Opal on her head, in the story, her Opal gets sprinkled by holy water, and it caused her to faint. When she woke up from her sudden faint, the opal had turned into ashes. The act of holy water turning the Opal into ash, made many believe that Opals were bad luck. The Opal in the story was a reminder of a tragedy that happened to her, the Opal turning into ash was supposed to symbolize her rebirth from that tragedy. In the end is just superstition.

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Geography of Opal

Opals form in many parts of the world, especially in semi-desert regions. Australia, Ethiopia, Peru, Brazil, and Mexico are the countries with the highest quality of Opals found in the market.

Map

Chemical Composition, Crystal Structure, and Physical Properties

Opals begin to form when seasonal rain drenches dry ground in semi-desertic regions. The water soaks deep underground carrying dissolved silica (a compound of silicon and oxygen, which is one of the key ingredients in sand) downwards. When the dry seasons return, much of the water evaporates, and it leaves behind solid deposits of silica. The deposits are found in cracks and layers of sedimentary rocks; the silica deposits forms Opals. The unique display of rainbow colors that is characteristic of this gem is called play-of-color. It is caused by submicroscopic spheres that are stacked on top of each other, like marbles in a jar. When light passes through these spheres it breaks the light into spectral colors, the size of the sphere determines the color it displays. Opals get divided into two classes: Precious Opals that shows play-of-color and common Opal that does not show this phenomenon. Opals have many variations, of which there are five main types:

White Opal– This Opal is translucent to semi-translucent, it displays play-of-color against a white or gray background color, the background color is also referred as body color.

white

Photo courtesy of GIA

 

Black Opal– This Opal is translucent to opaque, it displays play-of-color against a black or another dark background.

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Fire Opal– This Opal is transparent to translucent, with a brown, yellow, orange or red body color. This material often does not show play-of-color and is also known as “Mexican Opal.”

 fire

Boulder Opal– This Opal is translucent to opaque, displays play-of-color against a light to dark background. The unique feature of this Opal is the remaining fragments of surrounding rock, called matrix, become part of the polished gem.

 boulder

Crystal or Water Opal– This Opal is transparent to semi-transparent, with a clean background. This type of Opal displays exceptional play-of-color.

water

All Opals have a unique play-of-color, the colors they produce are exclusive to each one. No two Opals are alike.

 

Opal Jewelry

The unique displays of color combinations that Opal provides allow for designers to create pieces that feast the eyes. Most Opals are cut into cabochons, a smooth stone with no facets, a domed top and a flat or slightly domed underside. You will see them in necklaces, rings, and earrings. Some colors can be scarce and can demand a premium price. Here is an example of a white Opal pendant we designed.

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Wear and care of Opal

Opal has a 5.5-6.5 on the Moh’s scale. The Moh’s scale of mineral hardness characterizes the scratch resistance of various minerals on an exponential scale from 10 to 0. The top of the scale is Diamond at 10 and graphite at 0. Due to its low hardness, Opal is not ideal for heavy everyday wear. In the right mounting with the right protection, Opals will last a long time.

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The gentle touch of the rain as it falls and soaks the ground, it provides the perfect setting for a kiss under the rain or maybe just a romantic walk under the same umbrella with your significant other. Their simplicity makes them stand out from all the other gems, their colors are vivid, and their uniqueness from one another makes them even more appealing. So this October experience the wonderful world of color at Diadem Jewelers.

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