Rare Rocks! - Opal, 'The Precious Stone'

Throughout history, the opal has been considered to be lucky (the Ancient Greeks and Romans) and unlucky (Medieval Europe). Some say it is only lucky for those born within the month of October (lucky me!). Descriptions of opal are never mundane. Words such as pure, evil, precious, love and hope are used to describe this incredible gem. 

My description of the opal - Mysteriously Beautiful!

Massive Blue Banded Opal from the Barco River, Queensland, Australia. Photograph taken at the National History Museum, London, England. 
Photo released to Public Domain by author (Wikimedia Commons)

I love rocks and am known to go out of my way to visit rock shops!  I can spend hours in the study of how rocks are formed and in particular colored stones. Everything from quartz to diamonds! I find semi precious to precious gems to be beautiful reminders of just how incredible this world can be. It's a fascinating study, searching the origins of colored stones and realizing how each one has its own particular makeup. One sparkler that really gets my attention is the opal. Seeing a raw Australian boulder veined with flashing color is something special indeed. Understanding that this was actually a process of rain seeping into crevices and then the silica bearing waters drying into beautiful bands of striking color always confirms the mystery of nature. How does play of color occur? Read on to find out.  

I grew up with thinking of the opal as special to Australia. A majority of precious opal does comes from Australia. Mining areas such as Coober Pedy and Lightning Ridge used to conjure up images of mystery and adventure in my mind. 

Multi-colored rough opal specimen from Virgin Valley, Nevada, US
Photo released to Public Domain by author (Wikimedia Commons)

Opal appears in most parts of the world as common opal, with particular

countries producing precious opal. Ethiopia, now the hot spot for finding incredible finds, Mexico with their Fire Opals as well as the southwest USA are all big producers of precious opals as well as Hungary, the Czech Republic, Slovakia, Indonesia, Turkey and Brazil.

Beautiful play of color in this Ethiopian opal.

Common opal or what miners call 'potch' is opal that does not show any play of color. Common opal has a milky or pearly opalescence appearance. It comes in many different colors, such as black, white, colorless transparent, blue and purple.

Basic information to be considered when purchasing an opal:

• Color - Play of color and background color.  Play of color is microscopic spheres of silica which are arranged in an orderly manner. As light passes through the spheres it is diffracted, showing the colors of the spectrum. The colors are determined by the size of the spheres and the geometric makeup. 

'Spheres that are approximately 0.1 micron (one ten-millionth of a meter) in diameter produce violet. Spheres about 0.2 microns in size produce red.  Sizes in between produce the remaining rainbow colors.' (info provided by Gia.edu) 
When turned in the light, opals with play of color are incredibly beautiful.

• Pattern of play of color. There are many different patterns, such as pinfire, peacock's tail, palette, flagstone and exploding flash to name just a few. 

• Clarity - Transparency and whether there are inclusions or not. Inclusions in opals can be just as important to the functionality of the gem as well as the beauty of it, as opals with inclusions can fracture easily. 

Matrix is a term for where the opal is infused into the stone not just in the seams. Boulder opals are usually ironstone with opal forming in seams within the stone, showing as a vein.

Wood as well as shells can be opalized.

Petrified Wood with Common Opal -
Photo released to Public Domain by author (Pixabay)

There are several types of opal, such as black, white, jelly, boulder, crystal and fire. They all have different types of beauty and qualities. Black opal is usually considered the most valuable, depending on the quality of the stone. 

Opal is about 5.5 to 6.0 on the Mohs scale of hardness. That means that while it is a beautiful stone for the use of jewelry, consideration needs to be made on what type of setting is used. Much to my personal dismay, opal cracks rather easily. I found out about that aspect of my favorite stone the hard way by having a beautiful ring crack. Best not to use a prong setting for a ring. There isn't enough protection. A bezel setting is much better. Opal is best used in earrings, brooches and necklaces where they have less of a chance to receive rough contact with other surfaces. Opals can also crack or splinter due to dryness. They need moisture and do not do well stored in sunlight or heat. Most opals are cut and polished in the form of a cabochon.

Mexican Fire Opal - Intense, brilliant colors!
Fire Opals may have some play of color, but the term refers more to the intense colors of the opal, usually reds, oranges and yellows.
Photo released to Public Domain by author (Wikimedia Commons)

Ancient Romans gave opal its name, 

'opalus' which means 'Precious Stone'. 

The opal symbolized 'love and hope' 

in the Roman society.
(info provided by Gia.edu)

Australian Precious Opals with Matrix
Photo by Laurie A

Opals will be revisited in this blog as there is still so much to tell about this incredible stone. As with most gemstones, there is a great deal of lore regarding opals and I can't wait to tell you more about them. 

Sources:

Opalsdownunder.com

Australian Precious Opal by Archie Kalokerinos

Gia.edu

Geology.com

Search4gems.com

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Happy Thanksgiving!

Great Smoky Mountains, TN, some truly awesome rocks!

Thanksgiving Day is here and I've finally given myself permission to do some reminiscing about what I am truly thankful for. With the subject of this blog in mind, I think a story from my childhood is a good start to explaining why I feel that I am a blessed person.

As a child, I loved to collect rocks. It wasn't unusual for me to grab a grocery bag and con my mother into accompanying me for a children's version of a rock hound expedition. The couple blocks that would take us to an area that had a sloped hill filled with the objects of my quest were a chance for my mom and I to have some quality time together. We would diligently search through piles of stones, looking for the 'pretty' ones. My concentration was truly dedicated to the subject at hand and the walk home would be filled with questions about the incredible finds that I had collected. My mom, who probably wasn't nearly as interested in rocks as I was, did her best to field the questions and always encouraged my youthful enthusiasm in regards to my hobby.

My dad was also very much a part of my geological education. Boxes of 'pretty' stones soon appeared after he realized my interest in them. He took the time to study with me and I began to learn about my hobby. Soon I knew that amethyst and citrine were both quartz. I learned that moonstone wasn't really from the moon (although ancient Romans and Hindus both believed it was formed from moonlight), but is actually a feldspar, which shows aspects of adularescence, having a milky or bluish iridescence. When cut in a cabochon, the moonstone sometimes displays chatoyancy, a changeable luster, such as a cats-eye.

That the beautiful opal, my birthstone, shows play-of-color and is formed when

Opal vein. What a beautiful gift from nature!

rainwater soaks down into the earth, along with dissolved silica. When the rain evaporates, the silica is deposited between layers of sedimentary rock. The dissolved silica then forms the opal. Opals always conjured up visions of Australia, so very far away from home. Mines with names like Coober Pedy and Lightning Ridge, revved up my imagination of adventure and intrigue. I'm astounded by the beauty of the opal. This photograph of a true opal vein shows the results of this incredible process. You wouldn't think it could actually be real, but I saw it for myself when my parents visited Australia and brought a natural rock with an opal vein running through it back home with them.

My parents gave me the awesome opportunity to attend the University of Wisconsin, another reason to consider myself to be truly blessed. One of my favorite college classes was geology, where I learned about the layers of earth. About fossils and minerals and rocks. About eras and eons. I soaked the knowledge in and have never seemed to want to forget it. In later years I took my first class in gemology. I learned about colored gemstones and again, the information has stuck with me forever. 

Being able to grow in knowledge is such a blessing in itself. The advantages I had of learning about this incredible planet was just one of hundreds of blessings that my parents bestowed upon me. They were always interested in me and what I was interested in.   

So, on this Thanksgiving Day, I give thanks that I had the best parents that a person could possibly ever have. That I have a fantastic family and great friends and that I live in a country that still holds tremendous opportunities for learning, success and happiness.

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