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Roger Weller, geology instructor

wellerr@cochise.edu

Opal- History
by Sophia Monge
Physical Geology
Fall 2015
  
 
                                              
The History of Opal

 

When?
 

The earliest known opal that was discovered dated back to around 4000 B.C. The opal artifact were said to be found in Kenya by an anthropologist named Louis Leaky. The opals were discovered in a similar way any other precious gemstones were found, in a cave mining process, and were slowly practiced on to create different shapes for things such as jewelry. The most popular opals are found in Australia, Mexico, and the U.S.
 

gemstory.com.au
 

What is it?
 

The opal, however, is not a true gemstone or a mineral, rather it is commonly known as a mineraloid. The way to pick out an opal is by its color. The most common colors could include white, yellow, orange, purple, blue, green, grey, black, and brown. The colors, however, could change when looked at in different lighting and different angles. On the scale of hardness, the opal come in at around 4.5-6.5, according to the minerals.net website.  The composition of an opal is “Hydrous silicon dioxide. The water can range from 3% to 21% of the total weight, but is usually between 6% to 10%” (minerals.net) and the chemical formula is SiO2 · nH2O
 

R. Weller/ Cochise College
 

Most Popular
 

Though there are many different types of opals in the world, such as the fire opal, Idaho star opal, Arizona blue opal, and the Mexican jelly opal, the Australian black opal is the most valued opal. It is very rare to find, very rare in color and “have a dark background and colours ranging from brilliant red through to greens, blues and purples.”  (Australian Mines Atlas).  The name black opal comes from the definition of the opal having a black or grey base color; a lot of people mistake the black opal as being just that, a black tone based opal.
 

How Much?

If one were lucky enough to find a black opal with one grey-based side and one black-based side, it would be called a reversible opal. The first black opal was found in 1873 however, people were not aware of how much a black opal was worth until 1903. During that time the black opal was very valuable and the net worth of the opal only increased as time went on. According to the opalauctions.com website, the black opals were always the buyers top choice and the price could increase up to 20% per year. Some black opals value could range between $1,000-$3,000 per carat.
 

R. Weller/ Cochise College
 

How it is Valued

The way most opals are valued now could include the following; Opal class, body tone, play of colors brilliance, pattern, color bar, and faults. Though not all opals go through this specific checklist because of their uniqueness, a lot of the previous factors are taken into consideration when valuing each opal.  The most important factor though, is the body tone. The body tone determines what color it is and what kind of opal it is. It could be a black opal or even a light opal and generally the opals that have a darker undertone are higher valued opals than ones with the lighter undertone due to the darkness showing off the different colors better in the light.
 

Opalsdownunder.com
 

            Above is a general chart that can be used when determining the value of an opal and its color base and body tone within the opal.

           

How Jewelry is Made
 

The most common use for the opal is for jewelry and accessories. Having two ring, earrings, and a necklace with opals in them, I value them because I know how precious opals can be. In the jewelry most opals are solid stone but others are not. Some of the not so solid opals have very fine but brilliant layers. The way those opals are handled are by gluing the fine layer to its base of whatever jewelry the opal is going into, and then it has a cap put over it protect it from any wear and tear and damage to the opal itself. There are three ways to set an opal into jewelry; the solid opal, which has no covering on it, the opal doublet which is a thin layer of the opal glued onto a base, and the opal triplet with is a thin layer of the opal glued to the base and covered with a clear gap. An opal doublet and an opal triplet are worth a lot less than a solid opal would be worth.
 

Geology.com
 


 

      Above are pictures of my own opal rings. These rings value between $80 and $115.  The oval shaped ring is more of a doublet because the opal itself is very thin. I am not exactly sure how much the heart shaped ring is because it was a gift. It is a decent shaped opal but it is also very light in color while the oval shaped one is more of a blue color.
 

Fun Fact
    
For the month of October the birthstone happens to be the opal. According to the red C jewels website the meaning of the opal is “purity, innocence, and hope. The opal has metaphysical properties of confidence, loyalty, faithfulness, and happiness”. The name “Opal” could also mean “’To see the change in color’”. (Birthday gems.org)
 

 

Mexican Jelly Opals R. Weller/Cochise College
 

Synthetic Opal R. Weller/ Cochise College
 

Arizona Blue Opal. R. Weller/ Cochise College
 

Resources

·         https://www.opalauctions.com/learn/a-z-of-opals/australian-black-opal-information

·         http://www.gemstone.org/index.php?option=com_content&view=article&id=99:sapphire&catid=1:gem-by-gem&Itemid=14

·         http://skywalker.cochise.edu/wellerr/opals/List.htm

·         http://www.opalsdownunder.com.au/learn-about-opals/intermediate/history-opal

·         http://www.minerals.net/mineral/opal.aspx

·         http://www.australianminesatlas.gov.au/education/rock_files/opal.html

·         http://www.gemstory.com.au/basic3-black-opal.html

·         http://geology.com/gemstones/opal/

·         http://www.birthdaygems.org/october-birthstone.htm

·         https://redcjewels.com/october-birthstone-opal-meaning/