What's an Opal?
Have you ever wondered how an opal is formed? How old is it? What is it? Well, here are some answers to those common questions.
Opal is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica rich solution into cracks and voids, caused by natural faults or decomposing fossils. As the water evaporates, it leaves behind a silica deposit or little silica balls. This cycle repeats over very long periods of time, and eventually when the silica balls harden, compact, and form into rows and layers an opal is born! The solution is believed to have a rate of deposition of approximately one centimeter thickness in five million years at a depth of forty meters. What makes the colors in an opal? When light enters the stone it is sent back out by a process called Diffraction. The silica balls break up the light into rainbow colors known as Play Of Color or Fire.
Sunlight is made up of the whole range of colors that the eye can detect. The range of sunlight colors, when combined, looks white to the eye. This property of sunlight was first demonstrated by Sir Isaac Newton in 1666. Light of different colors is refracted by different amounts when it passes from one medium, air, for example, into another, water or silica, for example, and at different angles. That is what causes the colors in an opal and determines what colors the opal will show. You could think of it like a rainbow after a sun shower or a glass prism. Not exactly the same, but you get the idea. So, an Opal is a natural miracle of sorts, and a very special thing. Its' no wonder that opal was one of Queen Victoria's favorite gems!
The first opal that we know about was recorded in history during the Roman times, and it became popular around the late 1800s, and it is the birthstone for October. Opal today is mined in several parts of the world including Australia, Mexico, Brazil, Canada, USA, and Ethiopia. The majority of the opal on the market today is mined in Australia. Australia is the opal capital of the world.
Opal is not for everyone though, Opal is brittle, heat sensitive, and breaks and scratches easily; and if allowed to dry out for a long period of time it can result in fine cracks that extend over the surface until they intersect and cause the gem to break apart and crumble. This process is called crazing and occurs over a very long period of time under the most undesirable conditions. On the Mohs Scale of Hardness, where talc is rated 1 and diamond ends the scale at 10, opal is rated 5 through 6. Nevertheless, opal is still a premier and sought after gemstone throughout the world today. Never wear an opal while playing tackle football or rock gardening! Opal is also sensitive to drastic and severe temperature changes. An example of that would be doing the dishes in hot water while wearing an opal ring, then sticking your hand directly into the freezer to retrieve some ice. Not a good idea! Low humidity can cause an opal to dry out and fracture. Never store opals in a bank deposit vault as they have dehumidifiers that make the air extremely dry. If you live in a an area with low humidity, it's a good idea to soak your opal in pure distilled water a few times a year to keep it hydrated.
Different Types of Opals On The Market Today
There are many varieties of Opal on the market today. When buying Opal, do your homework! The values range from a couple of dollars to priceless gems. Let's start with some the least valuable types first. Typically, those are the stones that are man made or treated in someway. Here are three examples of treated opal or lab created opals.
- Doublets: A doublet is a very thin slice of opal glued to an onyx backing.
- Triplets: A triplet is simply a doublet with a clear cap glued onto the top.
- Gilson or Lab Created Opal: Created by Pierre Gilson Sr. in 1974 in a laboratory in France. These man made opals have all the elements of natural opal except water, which makes them equally beautiful but not prone to breaking. A trained eye can spot one.
Natural Precious Opals
There are many varieties of natural precious opals, here are the most popular types of opals.
White Opals: White based Opals are opaque and more common, but can have very strong color flash and can be very beautiful depending on the individual stone and the intensity of the play of color.
Crystal Opals: Crystal Opals are called Crystal Opals because they have a translucent or semitranslucent base, and they are usually very bright, depending on the individual stone. A high quality Crystal Opal looks almost like a rainbow, they are very special stones and command a pretty hefty price depending on the play of color.
Semi-Black Opals: Semi-Black Opals have a darker base color that ranges from Light to Medium Gray depending on the individual stone and usually have very vivid colors and also command a hefty price depending on the play of color. The base color can range from opaque to translucent or semitranslucent.
Black Opals: Most black opal is a blush-green color but can be any combination including gold, red, violet, yellow, and orange. Probably the rarest of all gems including fancy color diamonds is a very black, dark background with reds/pinks and other colors splashed across the stone with intense brightness and a "dance" that no stone can match. The top stones of this description can command $40,000 or more per carat. A Harlequin pattern black opal is so rare that it can be compared to a red diamond.
Different Flash Patterns
The patterns an opal shows can increase values dramatically when it's an unusual or rare one. There are several distinct patterns that are rare and very desirable that are found in very few Opals. These patterns command very high prices because of their rarity and beauty. They are Harlequin, Flagstone, Ribbon, Straw, Rolling Flash, and Chinese Writing to name a few. I will define the ones that are most popular.
Harlequin: A rare and very beautiful pattern in which the opal shows square or angular blocks of color arranged very closely together. This is my own personal favorite pattern.
Picture: This is a pattern when the colors naturally form a picture or appear to be a specific object.
Broadflash: Large sheets of color cover a large section of the stone or even the entire stone.
Rolling: This is a pattern where the colors seem to float across the stone when it's turned. Another one of my favorites.
Ribbon: This is a form of a rolling flash, but the colors are in rows or ribbons of colors that roll across the stone.
Working With Opal
Cutting Opal is alot of fun!
Opal cutting isn't for everyone, it's quite messy, your hands get cut up often, alot of times you are disappointed, but when you cut a winner it's all worth it and you can't wait to go back and try again.
When Opal comes out of the ground, most often it looks like a chunk of dirty rock, nothing important at all. Here is a picture of some dark based opal rough as it looks after it's dug out of the earth.
Not very pretty? You would be surprised what that ugly hunk of nothing can turn into under the right circumstances! You take that hunk of nothing and start cutting away at it to find the gemmy opal that is waiting inside. Good quality opal rough that will produce an expensive gemstone is extremely expensive and getting harder and harder to find these days.
A lapidary machine is what is used to cut opal rough, and it's a motor driven unit with several wheels on it that have different grits which range from very course to super fine polish. Starting with the course wheel, you cut and cut until you are close to what you want, and then you work your way over to the finer grit wheels for shaping, and then the final wheel for polishing until you achieve your finished stone.
An experienced cutter can turn that hunk of rock into just about anything that he or she wants. You can let your imagination run wild, you are the driver. Different shapes are always fun and it allows you to be creative and have fun!
An experienced goldsmith can take that loose stone and create the jewelry that lights up a room. All it takes is alot of experience, patience, steady hands and alot of praying that nothing goes wrong. Here are a few of my own personal favorites that I have made over the years. As you can seee, the possibilities are endless as opal is such a versitile gem. A little imagination and alot of hard work and a wearable work of art is born!
There is so much to learn about Opal, it's one of those gemstones that has so many different, unique, and beautiful faces. Opals can be compared to snowflakes, no two are alike. There are so many variables with opal, base color, flash color, flash pattern, translucent or opaque, and the list goes on and on. But that's the best part! Because there are so many variables with Opal, you could have hundreds of them and they could all be different. That's what makes it such a fun and unique gemstone to study, work with, collect, and enjoy.
If you want to learn more, I would highly suggest purchasing the book Opal Identification and Value by Paul B. Downing, Ph.D. He is a world respected opal authority and has dedicated a good part of his life studying opal and educating people about this amazing gemstone.
I hope you have enjoyed reading this page and I hope I have been able to shed some light on some common opal questions. I wish everyone knew about opals, they truly are one of the most fascinating things on earth.
Edward Saget, 30 Year Master Goldsmith and Graduate Gemologist
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